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Skandalakis’ Surgical Anatomy > Chapter 28. Pelvis and Perineum >

Pelvis and Perineum: Introduction


The history of surgery of the pelvic sidewall, pelvic floor, and perineum is the history of the organs within. Therefore, this history is not addressed here, but is presented in the chapters that pertain to each individual organ.

Pelvic Sidewall


The anterior and posterior compartments of the limb bud mesoderm are responsible for the genesis of the pelvic bones. Specifically, the pubis and ischium are of anterior origin, and the ilium is of posterior origin. The scope of this chapter does not include embryologic details of the several anatomic entities forming the pelvic wall or their congenital anomalies.

Surgical Anatomy


During lower abdominal surgery, the pelvic wall is the source of most of the surgical problems, anatomic complications, and technical difficulties. General surgeons, urologists, and gynecologists must be very familiar with the topographic anatomy of the pelvic wall. Oncologic surgeons depend on this information to perform their radical operations for the cure of cancer.

Fragmented knowledge of pelvic anatomy has resulted, perhaps predictably, from the development of specialties related to specific organ systems. Thus, specialists in the treatment of colorectal, urologic, and gynecologic problems, for example, may operate in adjacent regions and yet possess very restricted knowledge of the clinical anatomy of nearby structures. Whorwell et al.3 have pointed out, for instance, the tenfold increase in instability of the bladder detrusor muscle in patients who exhibit irritable bowel syndrome. It is important for the pelvic organ specialist to become familiar with the disorders of neighboring pelvic structures and the techniques for evaluating them.4

“True” and “False” Pelvis

The concept of “true” and “false” pelvis is useful for the urologist, gynecologist, and urogynecologist, but for many surgeons operating in the lower areas of the abdominoperitoneal cavity, this distinction is of little practical value.

It is difficult to pinpoint the organs that reside only in the true or the false pelvis. In this chapter, we include descriptions of anatomic entities that extend, or can extend, above the pelvic brim. We hope this does not confuse our reader.

True (Lesser or Minor) Pelvis

The true pelvis is the area between the pelvic brim and the floor of the pelvic cavity, bounded by the linea terminalis above and the pelvic and urogenital diaphragms below.

The pelvis contains portions of the urinary, genital, and digestive tracts. The distal portions of the ureters, urinary bladder, female genitalia, prostate gland, rectosigmoid, proximal rectum, and small bowel are discussed in other chapters of this book.

The promontory of the sacrum and the iliopectineal line form the pelvic brim. The pelvic diaphragm below, with participation of the urogenital diaphragm, forms the floor of the pelvis. The sacrum, hip bones, and the two paired muscles (piriformis and obturator internus) and associated fasciae form the pelvic wall. The greater sciatic foramen transmits the piriformis muscle, sciatic nerve (Fig. 28-1) and other vessels and nerves of the gluteal and perineal regions.

Fig. 28-1.

Top: Right posterior view of pelvis. Inset: Right lateral internal view showing sites of potential hernias through sciatic foramina. A, Suprapiriformic sciatic hernia. B, Infrapiriformic sciatic hernia. C, Subspinous sciatic hernia through lesser sciatic foramen. (Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair: The Embryological and Anatomical Basis of Surgery. New York: Parthenon, 1996, Plate 2-1C; with permission. Inset modified from Skandalakis JE, Gray SW, Akin JT Jr. Surgical anatomy of hernial rings. Surg Clin North Am 1974;54:1227-1246; with permission.)

The linea terminalis separates the false pelvis above from the true pelvis below. It is formed by the bilateral pubic crests and superior extent of the symphysis pubis, pectineal lines, arcuate lines, and midline sacral promontory. Inferior to the linea terminalis one typically finds the rectum, empty urinary bladder, non-pregnant uterus and its adnexa, vagina, terminal parts of the male reproductive system, sacral plexus, and pelvic neurovascular structures. Other elements, such as the greater omentum, transverse colon, sigmoid colon, and loops of small bowel (particularly ileum) provide unpredictable quantities of “temporary residents.”

False Pelvis

The intraperitoneal anatomy of the false pelvis is the downward continuation of the greater sac of the general abdominoperitoneal cavity. Its osseous boundaries are provided by the wings of the ilia (the flaring parts of the iliac bones of the pelvic girdle), the superior rami of the pubic bones, and the fourth and fifth lumbar vertebrae.

Bony Wall, Its Ligaments, and Its Internal Coverings

The relatively unyielding framework of the pelvis consists of several bones together with their associated ligaments. This includes the two os coxae or hipbones, the sacrum, and the coccyx. The piriformis and obturator internus muscles arise from the bony surfaces of the true pelvis. With their fascial coverings, these constitute the primary sections of the pelvic sidewall.

In addition, the bony foramina and their contents provide secondary limitations on the dimensions of the cavity of the true pelvis.

Structures occupying the foramina include distinctly occlusive entities, such as the obturator membranes. Also occupying the foramina are soft, yielding elements. Soft structures entering or leaving the pelvic cavity include the sciatic nerve and its branches, the obturator nerves and vessels, the gluteal neurovascular elements, and the internal pudendal arteries and veins.


The pelvis is bounded by the sacrum and coccyx posteriorly, and by the os coxae or hip bones anteriorly and laterally. The pelvic inlet (upper opening) is formed by the body and superior rami of the pubic bones and their pectineal lines, the arcuate lines of the ilia, and the sacral promontory. The pelvic outlet (lower opening) is formed anteriorly and laterally by the inferior rami of the pubis, the pubic symphysis and pubic arcuate ligament, and the rami and tuberosities of the ischia. Ligaments, sacrum, and coccyx are located posterolaterally and posteriorly.


The sacrotuberous and sacrospinous ligaments participate in the formation of the pelvic walls. They also serve to convert the greater and lesser sciatic notches into the greater and lesser sciatic foramina by their attachments to the sacrum and coccyx medially and the ischial tuberosity and ischial spine laterally.

Sacrotuberous Ligament

The sacrotuberous ligament (Fig. 28-1) originates at the posterior superior iliac spine and the lateral border of the sacrum and coccyx. It inserts upon the ischial tuberosity.

Sacrospinous Ligament

The origin of the sacrospinous ligament (Fig. 28-1) is the lateral border of the sacrum and coccyx. Insertion is upon the ischial spine.


Greater Sciatic Foramen

The greater sciatic foramen is five times larger than the lesser. It is formed by conversion of the greater sciatic notch into a foramen by the sacrospinous ligament.

The following anatomic entities leave the pelvis through the greater sciatic foramen (Fig. 28-2).

Fig. 28-2.

A, Right pelvic wall with deep muscles and sciatic foramina. B, Right gluteal region with sites of sciatic hernias. Gluteus maximus transected and reflected. (Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair. Pearl River NY: Parthenon, 1996; with permission.)


Piriformis muscle

Superior gluteal vessels and nerve (located superior to the piriformis)

Inferior gluteal vessels and nerve (located inferior to the piriformis)

Internal pudendal vessels and nerve (located inferior to the piriformis)

Sciatic nerve

Posterior femoral cutaneous nerve

Nerves of the quadratus femoris, obturator internus, and gemelli muscles (all leave the pelvis inferior to the piriformis)

Lesser Sciatic Foramen

The lesser sciatic foramen is formed by conversion of the lesser sciatic notch into a foramen by the sacrotuberous and sacrospinous ligaments (Fig. 28-2).

Several structures leave and enter from the lesser sciatic foramen. Leaving are the obturator internus and gemelli muscles, which arise from the edges of the foramen. The pudendal nerve, internal pudendal vessels, and the nerve to the obturator internus gain access to the perineum by passing through the lesser sciatic foramen.


The supra- and infrapiriformis foramina and the lesser sciatic foramen are potential sites of herniation (Fig. 28-1, Fig. 28-2).

Soft Tissues of the Pelvic Sidewall

The soft tissues of the pelvic sidewall consist of several layers. Their sequence from inside to outside is as follows.



Endopelvic fasciae

Internal iliac vessels, their branches, and associated smooth muscle and connective tissues

Parietal layer of pelvic fascia

Pelvic nerves

Paired obturator internus muscles

Piriformis muscles

Anatomic Layers

We present here, as a series of three anatomic layers, the various elements of the pelvic sidewall in the order in which they are seen when dissecting one layer of tissue at a time from the peritoneum to the bone of the pelvic sidewall (Fig. 28-3).

Fig. 28-3.

Anatomy of pelvic wall and pelvic diaphragm. A, Elements of the pelvic wall: skin to peritoneum. B, Frontal section of pelvis showing fasciae of pelvic diaphragm, obturator fascia, and pudendal (Alcock’s) canal. (Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair. Pearl River NY: Parthenon, 1996; with permission.)

First Anatomic Layer

The first anatomic layer includes the peritoneum and ureter. The ureter is held to the peritoneum by connective tissue elements, which, in some respects, resemble a mesentery.

Second Anatomic Layer

The second anatomic layer consists of the visceral branches of the internal iliac artery and vein, the endopelvic fascia, and the visceral nerves. Included in this layer are the vessels and nerves of the bladder, the internal reproductive organs, and the pelvic colon, together with the “pillars” of these organs. In the female, this layer also includes the specialized tissues of organ support, such as the cardinal and uterosacral ligament complexes and the pubovesicocervical fascia.

Third Anatomic Layer

The third anatomic layer includes the parietal fascia, obturator nerves and vessels, other neurovascular elements of the pelvic sidewall, and the obturator internus and piriformis muscles and their various fasciae.

Surgicoanatomic Layers

We acknowledge that the preceding order, although useful for anatomic clarity, does not fully reflect the layering of the pelvic elements as they are encountered in most pelvic surgical procedures. To the gynecologic or urologic surgeon especially, the following organization into five surgicoanatomic layers is more appropriate from a pragmatic point of view.

Now we present the anatomic entities of the pelvis both from a more technical, “surgicoanatomic” point of view, and also from a strictly “surgical,” practical viewpoint. We trust that the details of the anatomy and its application in these two differing approaches will converge in the mind of the reader. By employing these two schema, we hope to present the data as completely as we can without creating confusion.

First Surgicoanatomic Layer: Pelvic Peritoneum and Its Specializations

The pelvic peritoneum is described in the chapter on the peritoneum. Here we emphasize only the most important entities from a surgical standpoint.



The peritoneum does not reach the floor of the true pelvis in the adult.

Several organs of the digestive, urinary, and genital tracts are not completely covered by the peritoneum.

The pelvic peritoneum is associated medially with the urinary bladder, uterus, and rectosigmoid.

The pelvic peritoneum is associated laterally with the uterine adnexa, ureter, and the ductus deferens.

The ureter is fused intimately to the lateral surface of the peritoneum. If the peritoneum is incised and reflected medially, the ureter will be carried with it. The ureter can be released from the peritoneum only by sharp dissection, which carries the risk of producing localized ureteric ischemia.

The peritoneum of the pelvic wall is complicated by folds and fossae as it drapes over the midline organs of the urinary, genital, and digestive tracts.

Urinary Tract Reflections and Spaces

Several folds of peritoneum are associated with the urinary bladder. When these folds or ligaments seem to have some support function, they are called true ligaments; when they seem less supportive, they are called false ligaments. This distinction is arbitrary and unconvincing. The most important of these peritoneal ligaments are listed in Table 28-1.

Table 28-1. Ligaments of the Bladder

Ligament Location
True Ligaments   
Median umbilical ligament (urachus) (unpaired) Dome of bladder to umbilicus
Lateral true ligament Lateral wall of bladder to tendinous arch of pelvic fascia
Medial umbilical ligament (obliterated umbilical arteries) Inguinal ligament
Medial puboprostatic ligament (male) Pelvic wall to prostate gland
Lateral puboprostatic ligament Pelvic wall to prostate gland
False Ligaments   
Superior false ligament (unpaired) Covers the urachus
Lateral false ligament Bladder to wall of pelvis
Lateral superior ligament Covers the medial umbilical ligament
Posterior ligament (sacrogenital fold) Side of bladder, around rectum to anterior aspect of sacrum

Source: Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair: The Embryological and Anatomical Basis of Surgery. New York: Parthenon, 1996; with permission.

Lateral Umbilical Ligament

The bilateral, lateral umbilical ligament (peritoneum over the inferior epigastric artery and vein) (Fig. 28-4) is a helpful landmark for finding the ductus deferens when performing laparoscopic pelvic lymph node dissection and also for locating other inguinal entities in laparoscopic herniorrhaphies.

Fig. 28-4.

Path of inferior epigastric vessels. V, Vein; A, Artery. (Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair. Pearl River NY: Parthenon, 1996; with permission.)

Medial Umbilical Ligament

The bilateral, medial umbilical ligament (peritoneum over the obliterated portions of the umbilical artery) can be seen passing upward and medially toward the umbilicus (Fig. 28-5). Above the urinary bladder, at its apex, are the supravesical fossae. The supravesical fossae are separated by the median umbilical ligament (peritoneum over the urachus of the bladder). Lateral to the bladder are the paravesical fossae. The paravesical fossae are separated from the supravesical fossae by the transverse vesical fold, a horizontal fold of peritoneum which is most distinct when the bladder is empty.

Fig. 28-5.

Peritoneal relationships in the male. (Modified from Hinman F Jr. Atlas of Urosurgical Anatomy. Philadelphia: WB Saunders, 1993; with permission.)

Genital and Digestive Tract Reflections and Spaces


The vesicouterine pouch of the female lies between the upper posterior aspect of the urinary bladder and the body and fundus of the uterus (Fig. 28-6). The broad ligaments extend laterally to the pelvic sidewall. The uterosacral ligaments in the female extend backward from the cervix, embracing the rectum in their course. The uterosacral ligaments form the rectouterine folds with overlying peritoneum.

Fig. 28-6.

Peritoneal relationships in the female. (Modified from Hinman F Jr. Atlas of Urosurgical Anatomy. Philadelphia: WB Saunders, 1993; with permission.)

The rectouterine folds bound the rectouterine pouch (of Douglas) on each side. The rectouterine fossa or pouch separates the urinary bladder, or the uterus and posterior vaginal fornix in front, from the rectum and rectal ampulla behind.

Between the uterosacral folds and the lateral wall of the rectal ampulla are the pararectal fossae, which communicate with the rectouterine pouch.


In the male, the counterparts of the uterosacral ligaments are the sacrogenital ligaments.

The rectovesical fossa, the male counterpart of the pouch of Douglas, separates the rectum from the urinary bladder and seminal vesicles in front. More superiorly in the pelvis on the left is the intersigmoid fossa (Fig. 28-7).

Fig. 28-7.

Intersigmoid fossa. (Modified from Decker GAG, du Plessis DJ. Lee McGregor’s Synopsis of Surgical Anatomy (12th ed). Bristol: Wright, 1986; with permission.)

Relations of the Intersigmoid Fossa

The peritoneum is anterior to the intersigmoid fossa. Posterior to the fossa are the bifurcation of the left common iliac artery and the passage of the left ureter into the true pelvis. The sigmoid mesocolon and its contained vessels, such as the sigmoid artery, are above and to the right of the fossa.


The apex of the intersigmoid fossa is a landmark for finding the left ureter. With a finger in the fossa, the left ureter can be rolled on the underlying left common iliac artery.

Second Surgicoanatomic Layer: Blood Vessels of the Pelvis

General Topography of the Vessels

Between the peritoneum and the parietal pelvic fascia are the arteries and veins for the pelvic wall and viscera. The two main vessels are the bilateral internal iliac artery (Fig. 28-8) and internal iliac vein (hypogastric artery and vein) (Fig. 28-9). In the upright anatomic position, the artery and vein pass in the vertical plane along the pelvic sidewall. Their branches generally pass medially and inferiorly to reach the pelvic viscera. They carry with them the heavy connective tissue mantle called the hypogastric sheath that assists the vessels in providing direct support to the organs. The reader should consult the classic and beautiful work of Uhlenhuth et al.5 for a detailed description of the hypogastric sheath and its derivatives.

Fig. 28-8.

Internal iliac (hypogastric) artery branches into anterior and posterior division. Superior gluteal artery passes through superior portion of greater sciatic foramen. Inferior gluteal artery enters foramen below piriformis muscle. Inferior gluteal artery gives off superior and inferior vesical arteries and obturator artery before entering foramen. [Two unpaired arteries in the pelvis, the median sacral and superior rectal, are not shown.] All these arteries enter the pelvis extraperitoneally and may be ligated with impunity. (Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair. Pearl River NY: Parthenon, 1996; with permission.)

Fig. 28-9.

Veins of female pelvis. (Modified from Hinman F Jr. Atlas of Urosurgical Anatomy. Philadelphia: WB Saunders, 1993; with permission.)

The visceral branches of the internal iliac artery and vein, together with visceral nerves, endopelvic connective tissues, and smooth muscle form the “second surgical layer” for the surgeon operating on the pelvic organs. When attempting to arrest hemorrhage arising from visceral blood vessels, it is within this layer that one attempts to clamp, ligate, or clip the injured vessel or its ultimate source.

Other arteries are the unpaired median (middle) sacral, the distal portion of the inferior mesenteric artery with sigmoid branches and superior rectal branch. All enter the pelvis retroperitoneally and all can be safely ligated.

The rectal venous plexus (Fig. 28-9) is formed by the superior and middle rectal veins. The rectal venous plexus drains the rectosigmoid. From this plexus, drainage is to the inferior mesenteric vein (portal) and internal iliac vein (systemic). The uterine venous plexus drains to the internal iliac vein (systemic).

Topography of the Branches

The surgeon should remember the topography of the bifurcations of the arterial and venous systems.

Abdominal Aorta

The abdominal aorta (Fig. 28-8) bifurcates into the two common iliac arteries approximately at L4, 1 cm to 2 cm below and to the left of the umbilicus. When a thin, supine individual elevates the pelvis to displace the intestine, the pulse can be palpated at the bifurcation and the external iliac arteries can be felt at the pelvic brim.

Sacral Arteries

The median sacral artery (which springs from the posterior aortic wall) is often forgotten by the surgeon. Despite its small size, it can produce bleeding when lacerated in the operating room. In some individuals, branches of this artery and the lateral sacral arteries ascend through the ventral sacral foramina to supply sacral and lumbar nerve roots and even contribute to the arterial supply of the caudal part of the spinal cord.

Inferior Vena Cava

The inferior vena cava is formed from the two common iliac veins about 2 cm to 3 cm inferior to the umbilicus (Fig. 28-9, Fig. 28-10).

Fig. 28-10.

Venous pathways. (Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair. Pearl River NY: Parthenon, 1996; with permission.)


The right common iliac artery crosses in front of the left common iliac vein. This relationship is thought to be associated with the greater frequency of deep venous thromboses of the left common iliac vein and veins of the left lower limb. Inferior vena cava reflux associated with tricuspid regurgitation has been implicated in pelvic congestion syndrome.6

Wohlgemuth et al.7 recommend percutaneous transluminal angioplasty, stenting, or both to treat pelvic vein stenosis following surgical thrombectomy.

Common Iliac Artery

The bifurcation of the common iliac artery into internal and external iliacs is located at the level of the pelvic brim, opposite the sacroiliac joint (Fig. 28-8). Less commonly, however, this bifurcation may be just above or below the joint. This is especially true in individuals with more tortuous vessels, in some cases associated with vascular disease.

Internal Iliac Bifurcation

The bifurcation of the internal iliac into anterior and posterior divisions is usually very close or slightly distal to its origin at the common iliac. After this last bifurcation the key number to remember is three. The posterior division has three parietal branches. The anterior division has three parietal branches and three visceral branches.

These patterns are quite variable. Branches of the internal iliac can arise as a “spray” of vessels with no distinct formation of anterior and posterior divisions.

Terminal Branches of Posterior Division of Internal Iliac Artery

Three parietal arterial branches typically originate from the posterior division of the internal iliac. These are the iliolumbar, superior gluteal, and lateral sacral arteries (Fig. 28-8), discussed below.

ILIOLUMBAR ARTERY. The iliolumbar artery is located behind the obturator nerve. It passes deep and laterally under the psoas muscle to supply the iliacus muscle and other tissues in the iliac fossa.

SUPERIOR GLUTEAL ARTERY. The superior gluteal artery is related to the sacral plexus. It most commonly passes between the lumbosacral trunk (formed by the junction of descending branches from L4 and L5) and the ventral ramus of S1 at the upper border of the piriformis muscle. As they pass through the greater sciatic foramen, the superior gluteal artery and the superior gluteal nerve (from L4, L5, S1) lie against the rather sharp edge of the upper bony margin of the foramen. Here the artery is quite vulnerable to laceration or avulsion.

The superficial branch of the superior gluteal supplies the upper half of the gluteus maximus. The deep branch courses transversely anteriorly between the gluteus medius and minimus, supplying them. Both the superficial and deep branches have extensive anastomoses with other regional vessels, including the inferior gluteal, medial circumflex, lateral femoral circumflex, and perhaps others.

LATERAL SACRAL AND INFERIOR GLUTEAL ARTERIES. The lateral sacral arteries are in front of the sacral plexus. There are one to three lateral sacral arteries. These pass through the ventral sacral foramina, providing branches to supply vertebrae and spinal nerve roots. They may contribute to the blood supply of the spinal cord by long, ascending branches. The inferior gluteal artery, usually a terminal branch of the anterior division of the internal iliac, may leave the pelvis by passing between S1 and S2. In a significant number of individuals the inferior gluteal and obturator arteries arise from the posterior division.

Terminal Branches of Anterior Division of Internal Iliac Artery

VISCERAL BRANCHES. The anterior division gives origin to the following three or four visceral branches. All these branches remain within the pelvic cavity.


Umbilical, whose patent segment is the source of the superior vesical arteries


Inferior vesical

Middle rectal artery, in some cases

NOTE: The visceral branches of the anterior division of the internal iliac will be described in greater detail in other chapters on the organs to which the branches are related.

To the urogynecologist in particular, the visceral branching pattern can be of use in locating the uterine artery. After observing the obliterated portion of the umbilical artery, one can trace it proximally toward its origin from the anterior division of the internal iliac. The surgeon can then identify the superior vesical branch of the artery passing medially toward the bladder. Proceeding further proximally, one can then identify the uterine artery passing medially toward the vicinity of the isthmus of the uterus, and then note the passage of the uterine artery over the ureter (Fig. 28-11).

Fig. 28-11.

Ovarian and uterine arteries. Note location of ureter under uterine artery (“water under the bridge”).

PARIETAL BRANCHES. The anterior division also provides three parietal branches: the obturator, the internal pudendal, and the inferior gluteal. These arteries and their related structures (accessory pudendal, middle rectal, uterine and vaginal arteries) are discussed below.

Obturator Artery. The obturator artery is located below the obturator nerve at the sidewall of the pelvis. It passes through and exits the obturator foramen. In about 20 percent of individuals, the obturator artery arises from the superior gluteal artery. In 33 percent8 (or even more commonly), an aberrant or accessory obturator artery is present, arising from the inferior epigastric artery.

Gilroy et al.9 (Fig. 28-12, Fig. 28-13, Fig. 28-14) reported that 70-82% of pelvic halves and 83-90% of whole pelves had an artery, vein, or both in the variant position. Arteries were found predominantly in the normal position only, but normal and anomalous veins were most frequently found together. These data show that it is far more common than not to find a vessel coursing over the pelvic brim at this site; the implications for both pelvic surgeons and anatomists are obvious.

Fig. 28-12.

Schematic view of the right side of the pelvis showing normal (1) and variant (2) positions of obturator vessels. (Modified from Gilroy AM, Hermey DC, DiBenedetto LM, Marks SC Jr, Page DW, Lei QF. Variability of the obturator vessels. Clin Anat 1997; 10:328-332; with permission.)

Fig. 28-13.

Schematic summarizing the most common pattern for obturator arteries and veins with the range of percentages from the United States and China in parentheses. (Modified from Gilroy AM, Hermey DC, DiBenedetto LM, Marks SC Jr, Page DW, Lei QF. Variability of the obturator vessels. Clin Anat 1997;10:328-332; with permission.)

Fig. 28-14.

Summary schematic of the likelihood of encountering a variant obturator vessel on an individual pelvic side. (Modified from Gilroy AM, Hermey DC, DiBenedetto LM, Marks SC Jr, Page DW, Lei QF. Variability of the obturator vessels. Clin Anat 1997;10:328-332; with permission.)

Aberrant Obturator. When it originates from the inferior epigastric artery, the aberrant obturator is closely related to the ligament of Gimbernat. The aberrant obturator crosses medial to, lateral to, or directly over the femoral ring and over Cooper’s ligament. Infrequently, both an aberrant obturator artery and a normal obturator artery are present, with rich anastomoses at the obturator canal. Such a vascular arrangement is called the “circle of death”10 because of the profuse bleeding that can occur when either vessel is severed.

Internal Pudendal Artery and Vein. The internal pudendal artery is the more anterior of the two terminal branches of the anterior division of the internal iliac (Fig. 28-8). The internal pudendal artery leaves the pelvis by passing through the greater sciatic foramen. It crosses the sacrospinous ligament externally, just medial to the tip of the ischial spine. Here it accompanies the pudendal nerve (Fig. 28-15), formed from branches from S2, S3, and S4 at this location. The artery and its companion vein (Fig. 28-10) lie lateral to the nerve as they exit the pelvis inferior to the piriformis muscle. After crossing the external surface of the sacrospinous ligament and under the shelter of the more externally placed sacrotuberous ligament, the internal pudendal artery and its nerve enter Alcock’s canal to supply the tissues of the ischioanal (ischiorectal) fossa and the urogenital structures. Their distribution is described later in this chapter and in the chapters on the genital systems.

Fig. 28-15.

Alcock’s canal (dotted) and its contents. (Modified from McGregor AL, DuPlessis DJ. A Synopsis of Surgical Anatomy (10th ed). Baltimore: Williams & Wilkins, 1969; with permission.)

Accessory Pudendal Artery. Rather frequently, an accessory pudendal artery arises from the internal pudendal artery just prior to the departure of the internal pudendal through the greater sciatic foramen. This relatively unknown artery leaves the pelvis beneath the pubic arcuate ligament. It is related unilaterally or bilaterally to the midline deep dorsal vein of the penis or clitoris. The accessory pudendal artery occurs in about 10 percent of males, including its origins from the internal pudendal, obturator artery, and other, less common sources.11

Inferior Gluteal Artery. The inferior gluteal artery (Fig. 28-8) passes through the greater sciatic foramen with its companion inferior gluteal nerve (L5, S1, S2), medial to the sciatic nerve. This artery supplies approximately the lower half of the gluteus maximus and anastomoses richly with other arteries deep to that muscle.

Middle Rectal Artery. The middle rectal artery arises most commonly from or with the vesical, internal pudendal, or inferior gluteal arteries. It can arise directly from the anterior division of the internal iliac, as well as from the uterine artery.

The middle rectal artery has 3 characteristic features which caused Last8 to state that it is inappropriately named.


It is often reduced in size and sometimes absent, especially in the female.

Very little of the blood it transports goes to the rectum.

Most of its blood goes to the prostate.

Uterine Artery. The uterine artery crosses the floor of the pelvis in the parametrial tissue of the broad ligament. It arises most commonly from the same vascular stem that provides origin for the umbilical artery.

To find the uterine artery, identify the obliterated portion of the umbilical artery where it passes the urinary bladder. Here one can observe the origin of the superior vesical branch(es) to the bladder. Proceed proximally toward the origin of the umbilical artery, where one can then identify the uterine artery as it arises from the same vascular stem. From its origin, the uterine artery passes medially toward the uterine isthmus, accompanied by its veins and abundant connective tissue, soon crossing over the ureter (“water under the bridge”) (Fig. 28-11). This occurs approximately 1.5 cm (variably, 1 cm to 4 cm) from the uterine cervix. At the cervix, the uterine artery turns upward on the lateral wall of the body of the uterus in the broad ligament.

At the entrance of the uterine tube into the uterus, the uterine artery anastomoses end on with the tubal branch of the ovarian artery.8 The uterine artery is the principal source of arterial supply to the uterine tube in about 60 percent of cases.

NOTE: The uterine artery is the direct anterior visceral branch from the internal iliac artery. In many cases it arises as a branch of the patent portion of the umbilical artery. In the male, the homologue of the uterine artery is the deferential branch of the inferior vesical artery.

Vaginal Artery. The vaginal artery is often a separate branch of the internal iliac artery. In many cases the vaginal artery comes from the uterine artery. There may be more than one vaginal artery; multiple vaginal arteries may arise from the internal iliac or from the internal iliac and uterine artery. The vaginal artery supplies the highly vascular walls of the upper part of the vagina.8

According to Killackey,12 the rich anastomotic blood supply to the uterus from the ovarian, uterine, and vaginal vessels makes it difficult to cause devascularization injury when the uterus is removed during colorectal surgery, even with the most radical resection.

Summary of the Pelvic Arteries


Three parietal arterial branches leave the pelvis via the greater sciatic foramen:


– Superior gluteal

– Inferior gluteal

– Internal pudendal

The obturator artery leaves the pelvis via the obturator foramen.

NOTE: Any of these arteries leaving the pelvis can be ligated with relative impunity, taking care not to injure their fellow travelers, the nerves. If the internal iliac artery is occluded at its origin, however, or both gluteal arteries are ligated, gluteal ischemia can result.

All arteries of the pelvis enter it extraperitoneally. They are:


Unpaired median sacral artery (runs from L4 to the coccyx and behind the left common iliac vein, superior hypogastric plexus, and rectum)

Unpaired superior rectal artery

Paired internal iliac arteries

Collateral Circulation in the Pelvis

Arterial Circulation in the Pelvis

The eight potentially major pathways of collateral circulation after bilateral internal iliac ligation are:


Uterine artery with ovarian artery from aorta

Middle rectal artery with superior rectal artery from inferior mesenteric artery

Obturator artery with inferior epigastric artery from external iliac artery

Inferior gluteal artery with circumflex artery and perforating branches of the deep femoral artery

Iliolumbar artery with lumbar artery from aorta

Lateral sacral artery with median sacral artery from aorta

Anastomoses between vessels of bladder wall and abdominal wall

Anastomoses between internal and external pudendal arteries

The anastomosis of the middle rectal artery with the superior rectal artery and that of their corresponding veins can be extensive and significant (Fig. 28-16). The superior rectal artery is the terminal extension and downward continuation of the inferior mesenteric artery. It touches, but does not cross, the medial side of the left ureter, crosses the bifurcation of the left common iliac vessels, and descends into the base of the inferior limb of the sigmoid mesocolon to the rectum. The common iliac artery bifurcates at the pelvic brim opposite the sacroiliac joint.

Fig. 28-16.

Rectal vascular supply (highly schematic).

Venous Circulation in the Pelvis

Multiple small veins (Figs. 28-10, 28-16, 28-17) from the rectal plexus coalesce to form the superior rectal vein, draining by way of the inferior mesenteric vein to the portal system of the liver. Other rectal veins combine to form the middle rectal vein.

Fig. 28-17.

Right and left ovarian veins and branches of internal iliac vein.

Superior and inferior gluteal veins emerge through the suprapiriformic and infrapiriformic apertures of the greater sciatic foramen and form the internal iliac (hypogastric) vein. Veins from the uterine, vesical, or prostatic venous plexus unite with the middle rectal vein to contribute to the internal iliac vein. The internal pudendal vein emerges through the lesser sciatic foramen to join the inferior gluteal or internal iliac vein. There are many variations of venous drainage.

The internal vertebral venous plexus (Batson’s veins) (Fig. 28-18) is located within the extradural fat of the spinal canal. It communicates with the lateral sacral veins (a valveless system), then drains into the internal iliac vein.

Fig. 28-18.

Vertebral system of veins. (Modified from Decker GAG, du Plessis DJ. Lee McGregor’s Synopsis of Surgical Anatomy (12th ed). Bristol: Wright, 1986; with permission.)

NOTE: A sudden increase in pelvic pressure, such as from coughing, may produce venous reflux into the internal vertebral plexus. This can cause emboli because the blood courses through the posterior intercostal veins and into the superior vena cava via the azygos system. This route also provides an explanation for metastasis of cancer to the vertebrae and the skull. The brain and pelvic viscera are brought into association by this system.

 Read an Editorial Comment

Lymphatic Drainage in the Pelvis

Lymphatic drainage of the pelvic organs is shown in Table 28-2.

Table 28-2. Lymphatic Drainage of Pelvic Organs

Organs Groups of Nodes Receiving Vessels Draining Pelvic Organs
Ovary (along ovarian a.) Lumbar
Uterine tube (except part near uterus) (along ovarian a.) Lumbar
  Upper part of body Lumbar
  Lower part of body External iliac
  Cervix External iliac, internal iliac, and sacral
  Regional near uterine tube (along round ligament) Superficial inguinal
  Upper part (along uterine a.) External and internal iliac
  Middle part (along vaginal a.) Internal iliac
  Lower part Sacral and common iliac
  Part below hymen (with those from vulva and skin of perineum) Superficial inguinal
Testis and epididymis (along testicular a.) Lumbar
Seminal vesicle External and internal iliac
Ductus deferens (pelvic portion) External iliac
Prostate Internal iliac mainly; sacral and external iliac
Scrotum Superficial inguinal
Penis (clitoris)  
  Skin and prepuce Superficial inguinal
  Glans Deep inguinal and external iliac
Ureter (lower part) External or internal iliac
  Superior and inferolateral aspects External iliac
  Base External iliac mainly; internal iliac
  Neck Sacral and common iliac
  Female (along internal pudendal a.) Internal mainly; external iliac
    Prostatic and membranous parts (along internal pudendal a.) Internal iliac mainly; external iliac
    Spongy part Deep inguinal mainly; external iliac
  Upper part Inferior mesenteric
  Lower part Sacral, internal iliac, and common iliac
Anal canal  
  Above pectinate line (along inferior rectal and internal pudendal aa.) Internal iliac
  Below pectinate line Superficial inguinal

Source: O’Rahilly R. Gardner-Gray-O’Rahilly Anatomy: A Regional Study of Human Structure, 5th Ed. Philadelphia: WB Saunders, 1986; with permission.

Third Surgicoanatomic Layer: Pelvic Fasciae

Parietal Fascia

According to Last,13 the fascia of the pelvic wall is a strong, membranous layer covering the obturator internus and piriformis muscles that form the wall. The fascia is firmly attached to the periosteum at the muscles’ margins.

From our observations, the parietal fascia should also include that fascia which covers the pelvic surface of the pelvic diaphragm, that is, the levator ani and coccygeus muscles. This is consistent with the concept that the endoabdominal fascial lining is a continuum and called the fascia transversalis. This term refers to the apparent continuity of muscle fascia lining the abdominal muscles, including the inferior surface of the respiratory diaphragm above. Following this line of thought, we can view the muscle fascia lining the pelvic basin, both its sidewalls, and the floor as a continuing entity.

The parietal fascia of the pelvic basin is continuous with the parietal fascia of the false pelvis above. The parietal fascia also covers the “cracks” in the wall that are formed by the foramina. The superior and inferior gluteal blood vessels pierce this fascia to go to the buttocks, and the obturator nerve and vessels penetrate it to pass through the obturator canal.

Visceral Fascia

The visceral fascia (Fig. 28-19) is essentially the connective tissue that encapsulates the individual organs within the pelvis. This fascia can be named according to the organ it covers, such as vesical, rectal, or prostatic. The fascial encapsulation varies greatly in thickness over the organs of the pelvis. Where the organ passes through the pelvic floor, the visceral fascial capsule fuses with the adjacent parietal fascia of the floor.

Fig. 28-19.

Visceral fascia. (Modified from Sears NT. The fascia surrounding the vagina, its origin and arrangement. Am J Obstet Gynecol 1933; 25:484-492; with permission.)

In certain areas, adjacent structures display a nearly common fascia, and it is practical to apply a more inclusive name. For instance, beginning anteriorly at the pubic bones, there is a continuing mantle of feltlike connective tissue and smooth muscle fibers known as the pubocervical, pubovesical, or pubovesicocervical fascia. It covers the anterior wall of the vagina and joins the superior fascia of the pelvic diaphragm lateral to the vagina (or prostate gland). Here it forms a bilateral band extending from about 1 cm above the lower border of the pubic bone to the ischial spine, the arcus tendineus fascia pelvis, or “white line of the pelvis.” This connective tissue mantle is continuous also with the visceral fascia encapsulating the individual organs.

The relative density of the visceral fascia conforms with the distensibility of the organ. For example, the fascia covering the bladder and rectum is loose, while the fascia over the prostate is dense. The fascia that invests the organs contains the collecting channels of the lymphatic drainage from the organs. As noted by Uhlenhuth et al.,5 surgeons are well aware that after a malignant growth in an organ invades the connective tissue capsule, metastatic spread is likely.

Specializations of Endopelvic Fasciae

The connective tissues separating the peritoneum, visceral capsules, and parietal fascia of the pelvis and lower anterior abdominal wall are organized distinctively and predictably into several forms. Their variations in density and quantity of tissue are attributable factors of age, sex, state of health, obesity, and so on.

Numerous past and current studies of these structures show a lack of unanimity regarding both the nomenclature and details of the organization and significance of these bands, sheaths, and visceral ligaments. Sidestepping some of the more obvious areas of controversy, we suggest summarizing some of the fascial condensations as follows:


Neurovascular connective tissue sheaths and “pillars”

Derivatives of parietal fascia

Condensations of extraperitoneal connective tissue laminae

Peritoneal derivatives

“Bands” supporting organs from the fusion of visceral and parietal fascia

“Filling” tissue

Condensations of connective tissues and smooth muscle fibers accompany the vessels and nerves supplying the pelvic organs.

One such major “band” of tissue extends from and incorporates the branches of the internal iliac vessels to the midline pelvic organs. We compare this to a “vascular leash” to the viscera. This structure, with its derivatives, appears to be comparable with Uhlenhuth’s “hypogastric wings.”5 We find the cardinal ligament (also called the lateral cervical ligament, transverse cervical ligament, retinacula uteri or ligament of Mackenrodt) to be part of this complex, accompanying the uterine artery. Anteriorly, the so-called lateral pillar of the urinary bladder is also derived from this tissue. It continues superiorly toward the navel with the obliterated part of the umbilical artery.

Another condensation of connective tissue and smooth muscle is formed largely by presacral connective tissue with contributions from the piriformis muscle fascia. It appears to incorporate splanchnic nerve branches from the sacral plexus and elements of the pelvic plexus (inferior hypogastric plexus). We liken it to a “neural leash” for the viscera. Several important derivatives appear from this “confederacy” of connective tissue, smooth muscle, and neural elements arising as laminae passing into successive horizontal planes.

Muntean14 discussed the rectum and its fasciae and pelvic relations, observing the continuity of the presacral fascia with the lateral pillars of the rectum and with the arcus tendineus fascia pelvis, thereby forming a hammocklike support for the rectum. Further, the presacral fascia initially invests the pelvic splanchnic nerves and thereafter the right and left pelvic plexuses. We have observed that these nerve elements, plus connective tissue, smooth muscle, and overlying peritoneum, form the uterosacral ligaments. The left pelvic rectal stalk is usually thicker than that on the right side, because of the great number of ascending parasympathetic fibers destined to supply the descending and sigmoid colon.

We believe the forward extension of presacral fascia (fascia of Waldeyer) is continuous with the lateral pillar of the rectum. It receives the contributions of the superior and middle rectal vessels and their associated fasciae.

Just beneath the peritoneum of the wall of the pararectal fossa, this band is evident as the uterosacral ligament.

Anterior to the cul de sac of Douglas, the presacral band splits. Part of it continues as the uterosacral ligament and part diverges to continue with the rectovaginal septum (fascia of Denonvilliers).

At the level of the ischial spine, the neural and vascular leashes appear to be convergent with one another and with the arcus tendineus fascia pelvis.

The vesicoumbilical fascia is a triangular condensation of extraperitoneal connective tissue. It extends upward from the urinary bladder toward the umbilicus at the apex of the triangle. The urachus is in the triangle’s middle and the obliterated umbilical arteries arise laterally. A variable quantity of adipose tissue is incorporated between the anterior and posterior laminae of this fascia. This interesting, well-localized condensation of extraperitoneal connective tissue lies between the peritoneum and the transversalis fascia.

The bilaminar rectovaginal septum of the female separates the rectum from the posterior vaginal wall. Similarly, the bilaminar rectogenital septum of the male separates the rectum from the prostate gland anteriorly. The septum extends from one ischial spine to the other and is attached inferiorly to the perineal body (perineal center) and floor of the pelvis. The potential space (of Proust) lies between the two laminae of the rectogenital septum, and has been referred to, facetiously, as the “space between wind and water.”

The septum (fascia of Denonvilliers) is derived from the original attachment of the peritoneum to the pelvic floor. The septum is then lifted by the growth of the pelvic organs as a bilaminar layer of tissue that fuses at the floor of the rectogenital fossa. It varies in thickness by individual and is often bilaminar. The septum is of great value both in limiting the spread of disease and in providing a plane of access for surgical procedures.

The visceral capsules, vascular and neural sheaths, and the extraperitoneal spaces are occupied by widely varying quantities of adipose and areolar tissues and smooth muscle fibers. The vesicoumbilical specialization of the extraperitoneal connective tissue also varies greatly in the quantity of fat between the upper margin of the bladder and the umbilicus.

In the upright position, the bladder, uterus (anteflexed and anteverted), the majority of the vagina, and the rectal ampulla lie in horizontal planes, essentially parallel with the floor beneath the feet. These organs are suspended by hammocklike arrangements of connective tissue that extend from one side of the pelvis to the other. Following is a description of the hammock configuration.


The urinary bladder and urethra rest upon a hammock provided by the pubovesicocervical fascia that extends posteriorly from the pubis to the posterior fornix. This hammock is secured to the levator ani muscle laterally by way of the arcus tendineus fascia pelvis. The hypogastric sheath suspends the hammock from above.

The vagina reclines in a hammock formed by the rectovaginal septum which is attached below to the perineal body and laterally to the ischial spines (Fig. 28-20). This lateral attachment adds to reinforcement and suspension by the convergence of the cardinal and uterosacral ligaments at the pericervical ring and the adjacent region of posterior fornix.

The rectum is supported by the presacral fascia and the diverging connective tissues of the lateral rectal pillars.

Fig. 28-20.

Cross section of the pelvis through the vagina. Note the difference between the tendinous arch of the pelvic fascia (white line) and the tendinous arch of levator ani muscle. (Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair. Pearl River NY: Parthenon, 1996; with permission.)



In the female, the visceral fascia envelops the bladder, urethra, vagina, and rectum, and extends downward and anterior to the vagina and between the rectum and vagina. Here further specialization occurs posterior to the vagina in the fascia of Denonvilliers.

The cardinal ligament (lateral cervical ligament, transverse cervical ligament, retinacula uteri, or ligament of Mackenrodt) is a condensation of the endopelvic fascia. It is a thickening around the uterine vessels from the sidewall of the pelvis laterally to the cervix. It is considered by many to be formed merely of condensations of the blood vessel connective tissue sheaths, although it is recognized by others that the collagenous and elastic fibers are supplemented by smooth muscle fibers. The cylindrical shape of the uterine cervix is testimony to the fact that it lies within a ring of connective tissue investment, lacking the direct connective tissue attachments that act to flatten the vagina and bladder in the coronal plane.

The endopelvic fascia is a downward continuation of the endoabdominal fascia. As Davies15 noted, it is multilaminar with an outer membranous component and an inner layer characterized by adipose elements. These fascial layers lie between the peritoneum and the transversalis, lumbar, iliacus, or diaphragmatic fascia throughout the abdominopelvic cavity.

Urologists and gynecologists consider the pelvic floor to be formed by endopelvic fascia, the pelvic diaphragm and its fascial layers, undergirded by the urogenital diaphragm.

The pelvic parietal fascia covers the superior surface of the levator ani muscle (pelvic diaphragm). Both its superior and inferior fascial layers are continuous with the superior fascia of the urogenital diaphragm at the margin of the urogenital hiatus. The pelvic parietal fascia, a continuation of the transversalis fascia, covers two muscles (internal obturator and piriformis) and the pelvic diaphragm (levator ani and coccygeus).

The presacral fascia is part of the parietal layer of pelvic fascia. It is located posterior to the retrorectal space. Thick and strong, it covers the concave surface of the sacrum. Multiple veins, several arteries, and nerves reside beneath this fascia.

Some authors believe the urogenital diaphragm is covered with fascia superiorly and inferiorly and that both fasciae are continuous with the internal, or superior, parietal fascia of the pelvic diaphragm. McGregor and Du Plessis16 stated: “The inferior layer of the urogenital diaphragm has nothing to do with the pelvic fascia. At one time during evolution the pelvis had no gap beneath the symphysis. This was filled by a mass of bone. With the advent of mammals there was insufficient room at the pelvic outlet for the passage of the fetal head: the bony mass became replaced by fascia – the inferior fascia of the urogenital diaphragm. This is therefore the morphological representative of this one-time bony layer.”

More accurate evaluation of female pelvic abnormalities is becoming possible with advancements in newer high resolution CT scanners combined with mechanical intravenous contrast medium injection and thinner sections. Foshager and Walsh17 state that in order to reap maximum benefit from these improved technologies, medical professionals should be familiar with the CT appearance of the normal female pelvic anatomy and its variations.

Pozzi and Shariat18 have found that, even though the pelvic fascia and ligaments are very thin, they are well demonstrated (thanks to the natural contrast of pelvic fat) by high quality images of the latest CT scanners. The same authors report19 that the normally thin fasciae and ligaments tend to appear thicker in abnormal conditions, as in the presence of pelvic neoplasms. These thickenings are easily demonstrated on axial scans. They emphasize, though, that there are many possible reasons for thickening other than neoplastic disease.

Fritsch and Hötzinger,20 using CT scan and MRI, report that pelvic connective tissue consists of three compartments: presacral, perirectal, and paravisceral. Readers wanting to know more about these compartments should consult the work of Fritsch and Hötzinger.

Fourth Surgicoanatomic Layer: Nerves of the Pelvis

Some pelvic surgeons include the visceral nerves (Fig. 28-21, Fig. 28-22, Fig. 28-23) within the second surgicoanatomic layer, together with the vascular supply of the pelvic viscera. The parietal nerves then reside in the third surgical layer of the pelvis. For all practical purposes, from this philosophically pragmatic approach, the third layer includes the obturator nerve and vessels, external iliac vessels, and genital branch of the genitofemoral nerve (all residing on the medial pelvic surface of the psoas muscle) and the obturator internus and piriformis muscles and their muscle fasciae.

Fig. 28-21.

Superior gluteal nerve passing through superior (suprapiriformic) portion of greater sciatic foramen. Inferior gluteal nerve and posterior cutaneous nerve of thigh passing, with sciatic nerve, through inferior (infrapiriformic) portion of greater foramen. Lesser sciatic foramen traversed by pudendal nerve, nerve to obturator internus muscle, and internal pudendal artery and vein. (Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair. Pearl River NY: Parthenon, 1996; with permission.)

Fig. 28-22.

Right pelvic wall and nerve supply. Sacral and coccygeal plexus. Inset: Course of pudendal nerve. (Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair. Pearl River NY: Parthenon, 1996; with permission.)

Fig. 28-23.

Diagrammatic representation of the course of the sciatic nerve and the common peroneal and tibial nerves, and the nerve to the hamstring muscles. (Modified from Nakano KK. Sciatic nerve entrapment: the piriformis syndrome. J Musculoskel Med 1987;4:33-37; with permission.)

Havenga et al.21 define the autonomic nerves of the pelvis to include the paired sympathetic hypogastric nerve, sacral splanchnic nerves, and the pelvic autonomic nerve plexus. We quote from their excellent article:

The anatomy of the pelvic autonomic nerves is closely related to the anatomy and the fascial planes which form the retrorectal space. The rectum is surrounded by a layer of fatty tissue which contains the blood vessels, draining lymph vessels, and the lymph nodes of the rectum itself. This layer is referred to as the mesorectum. … Bladder and sexual dysfunction after rectal cancer surgery can be avoided in the majority of cases by identifying and preserving the pelvic autonomic nerves … [and] by teaching surgeons the anatomy of the pelvic autonomic nerves and the pelvic fascial planes …

Anatomically, several plexuses and nerves are related to anatomic entities within the pelvis. They are as follows.


Most superficial: anterior aspect of pelvic plexus for the rectum

Superficial: urogenital fibers for the urinary bladder, prostate, upper urethra, root of penis

Intermediate to deep: posterior aspect of pelvic plexus within the endopelvic fascia, passing forward in the endopelvic fascia just above the levator ani for the urinary bladder and prostate

Deepest: pudendal and sacral nerves anterior to the Waldeyer’s fascia (described previously in this chapter). The nerve to the levator ani (from S4 or S5) courses upon the pelvic surface of the coccygeus, iliococcygeus, and pubococcygeus and provides branches that pierce the superior fascia of the pelvic diaphragm to innervate the muscles.

The nerves of the pelvis include branches of the lumbar and sacral plexuses, the abdominal sympathetics, and sensory fibers. The pelvic nerves include the following bilateral neural elements:


Obturator nerves

Pelvic, sacral, and coccygeal plexuses and their derivatives

Pelvic splanchnic nerves

Sacral part of the sympathetic nervous system

Visceral Nerves of the Pelvis

The visceral nerve elements present within the pelvis include the nerves and plexuses supplying the pelvic organs with autonomic and visceral afferent supply.

The innervation of visceral peritoneum is poorly localized. Innervation is carried by nerves whose principal function is sympathetic (“fight or flight”). Pain is usually referred to the levels of the body wall associated with the cord levels at which the pain fibers enter. T11 – L2 serves the majority of lower abdomen and pelvis.

Pelvic Plexuses

The pelvic plexuses are seen especially well in the endopelvic tissues of the pelvic sidewall. These plexuses contain a mixture of parasympathetic and sympathetic ganglia. The pelvic plexuses are a mixture of sensory and autonomic fibers on the sidewall of the pelvis lateral to the rectum and within the endopelvic and visceral fasciae.

Inferior Hypogastric Plexus

Considerable lack of agreement exists in the literature regarding the terminology for the nerve plexuses in the lower abdomen and pelvis. The term “inferior hypogastric plexus” seems as unacceptable a name for a pelvic plexus of nerves as “hypogastric artery” for the internal iliac artery. Nonetheless, the name “hypogastric” is fixed securely in clinical parlance.

Anatomically, the inferior hypogastric nerves are located at the lateral pelvic wall, 1 cm to 2 cm medial to and parallelling the ureter. The nerves create a bridge between the superior hypogastric plexus and the pelvic plexus. According to Church et al.,22 the hypogastric nerves originate posterior to the superior rectal artery and move distally to 2 cm to 4 cm below the peritoneum (Fig. 28-24). Here, they continue downward with the pelvic parasympathetic nerves (nervi erigentes) which arise from S2 to S4 and form the pelvic plexus.23,24 The pelvic plexus is located at the lateral pelvic wall and at the level of the distal one-third of the rectum.

Fig. 28-24.

Relationship of rectum to surrounding fasciae, blood vessels, and nerves at various depths in male pelvis (schematic transverse section). Most of pelvic nerve plexus is laterally embedded in endopelvic fascia on pelvic wall. Middle rectal artery is separated from lateral ligaments. (Modified from Church JM, Raudkivi PJ, Hill GL. The surgical anatomy of the rectum: A review with particular relevance to the hazards of rectal mobilization. Int J Colorect Dis 1987;2:158-166; with permission.)

NOTE: The hypogastric nerves originate in the superior hypogastric plexus, located at the aortic bifurcation. When ligating the inferior mesenteric artery, be extremely careful not to violate the plexus and the left hypogastric nerves. We advise careful isolation of the artery.

Superior Hypogastric Plexus

The superior hypogastric plexus is located at the aortic bifurcation and has no named ganglia. It can be considered as the continuation of the preaortic plexus beyond the inferior mesenteric part of the plexus. The superior hypogastric (or, more simply, hypogastric) plexus divides into the right and left pelvic (inferior hypogastric) plexus.

Sympathetic Fibers

The sympathetic fibers of the pelvic plexus are vasomotor, motor to sphincters, inhibitory to peristalsis, and sensory for painful sensations for most of the pelvic viscera. The smooth muscle of the vesical trigone and the internal sphincter of the urethra are innervated through the hypogastric (presacral) sympathetic nerves. As far as we know, the testes and ovaries have good sympathetic supply but no definable or demonstrable parasympathetic supply.

The sympathetic contribution to the pelvic plexus derives in large part from the hypogastric plexus (mixture of pre- and postganglionic fibers) in front of the body of L5, forming the so-called “hypogastric nerve.” In addition, several branches arise as sacral splanchnic nerves from the sacral portions of the sympathetic chains and join the plexus.

NOTE: “Sacral splanchnic” nerves should not be confused with the “pelvic splanchnic” nerves, which are parasympathetic in function.

The sacral sympathetic trunks cross the pelvic brim just behind the common iliac artery and vein. They travel downward close to the concavity of the sacrum – in most cases medial to the anterior sacral foramina. The foramina are useful landmarks for the topography of the trunks.

The final destinations of the sacral sympathetic trunks is the conjunction of the two sympathetic chains, anterior to the coccyx. Here the right and left chains unite to form a ganglion, the so-called ganglion impar. All the sacral ventral primary rami receive gray communicating rami (postganglionic sympathetic fibers) from the sympathetic trunks.

Sir William Turner, when asked by a student where the sympathetic nervous system begins, roared in his deep voice, “the sympathetic begins nowhere.”8 Many advances have been made in our knowledge since those days, but much still remains to be learned about the autonomic system.

These statements characterize pelvic sympathetics:


Sympathetic fibers provide motor supply for the ducts and glands for ejaculation, including the urethra.

The sympathetic system seems to have little effect upon the colon and rectum.

Presacral neurectomy (resection of the superior hypogastric plexus) can be carried out with impunity only in females. Menstruation, pregnancy, and parturition can occur normally in the absence of sympathetic fibers to the pelvis. In the male, however, section of the presacral nerve results in sterility in 50 to 60 percent of patients.

Chen25 states that laparoscopic presacral neurectomy is an effective treatment for chronic pelvic pain and dysmenorrhea.

Parasympathetic Fibers

The parasympathetic part of the pelvic plexus is derived from branches of S2-S4. These are the pelvic splanchnic nerves (nervi erigentes). The nervi erigentes are motor and secretomotor to the gut from the splenic flexure to the rectum. The muscle of the bladder (detrusor muscle) and rectum are also innervated by the nervi erigentes, as are the smooth muscles of the internal sphincter of the anal canal. The erectile tissues of the penis and clitoris also receive their functional fibers for erection from the pelvic splanchnic nerves.

Parietal Nerves of the Pelvis

The parietal neural structures present within the pelvis include the paired obturator nerves, lumbosacral plexus, coccygeal plexus, and derivatives of these.

Obturator Nerve

The obturator nerve (anterior divisions of L2-L4) (Figs. 28-22, 28-25) is the chief nerve supply for the adductor compartment of the thigh. It contains skeletal motor fibers for the following muscles: obturator externus, adductor longus, adductor brevis, adductor magnus (anterior part), and gracilis. It provides sensory fibers for the intermediate part of the medial surface of the thigh and some sensory fibers for the knee joint.

Fig. 28-25.

Sagittal section of thigh showing the course of obturator hernia (dashed arrows) along obturator nerve and its branches. (Modified from McGregor AL, DuPlessis DJ. A Synopsis of Surgical Anatomy (10th ed). Baltimore: Williams & Wilkins, 1969; with permission.)

The obturator nerve traverses the pelvis only through extraperitoneal fatty tissue. The path of the obturator nerve follows.


Appears from beneath the psoas muscle

Crosses the pelvic brim medial to the sacroiliac joint to the angle between the external and internal iliac vessels, very close to the ovary. (Ovarian pain can be referred to the medial side of the thigh).

Passes vertically downward to the obturator foramen

Traverses the muscle fibers of the obturator externus at the obturator foramen

Divides into anterior and posterior divisions at the obturator foramen or somewhat more distally

The anterior division supplies the adductor longus and gracilis. The posterior division provides innervation for the adductor brevis and magnus.

Pellegrino and Johnson26 report bilateral obturator nerve injury secondary to prolonged urologic surgery. The nerve injury was believed to have resulted from stretching at the bony obturator foramen.

Ali27 reports a case of left tubal ectopic pregnancy presenting with left obturator nerve pain. More likely, however, tubal and ovarian pain is simply referred to dermatomes of intermediate lumbar spinal nerve levels, especially L2. This dermatome is supplied by the obturator nerve, in part.

The accessory obturator nerve, when present, passes over the superior pubic ramus and behind the femoral sheath. It supplies the pectineus muscle.

Lumbosacral Plexus

The lumbosacral plexus (L4-S5) (Fig. 28-26) is formed in the posterior wall of the pelvis by the lumbosacral trunk and the anterior primary rami of spinal nerves L4-S5.

Fig. 28-26.

Formation of lumbosacral trunk and further formation of sciatic and pudendal nerves (highly diagrammatic).

NOTE: L4 is shared both by the lumbar and sacral plexuses. A branch from L4 (the so-called furcal nerve) joins L5 to form the lumbosacral trunk. This trunk carries the L4 and L5 contributions to join the nerves of the sacral plexus.

The sacral nerves emerge from the anterior sacral foramina. They unite in front of the piriformis where they are joined by the lumbosacral trunk. Several of the branches from this plexus provide origin for nerves supplying the pelvic viscera (pelvic splanchnic nerves). Other branches provide innervation for the muscles of the pelvic floor and sidewalls. The motor branches of the sacral plexus lie deep to the endopelvic fascia and exit via the greater sciatic foramen (except for the nerve to the levator ani).

Branches of the lumbosacral plexus exiting the greater sciatic foramen include the pudendal nerve, nerves to the gluteal region, and the sciatic nerve. These nerves provide motor and sensory supply to the perineum, gluteal area, posterior thigh, leg, and foot.

Pudendal Nerve

The pudendal nerve (S2-S4) is the nerve of the pelvic floor and perineum (see Fig. 28-21, Fig. 28-22, Fig. 28-26). It emerges through the greater sciatic foramen in company with and medial to the internal pudendal vessels. The nerve passes over the sacrospinous ligament, then through the lesser sciatic foramen to gain access to the perineum. Laterally, in the ischioanal fossa of the perineum, the pudendal nerve traverses the pudendal canal of Alcock (Fig. 28-27), providing motor and sensory branches to the perineal skin, the external anal sphincters, and the muscles of the urogenital region.

Fig. 28-27.

Alcock’s canal (formed by pelvic fascia and fascia lunata). (Modified from McGregor AL, DuPlessis DJ. A Synopsis of Surgical Anatomy (10th ed). Baltimore: Williams & Wilkins, 1969; with permission.)


A single nerve, the pudendal, and a single artery, the internal pudendal, are responsible for most of the innervation and blood supply of the perineum.

The pudendal nerve (from S2, S3, S4) has three divisions and covers five territories. The divisions of the pudendal nerve are rectal, perineal, and dorsal genital nerve of the penis or clitoris.

Rectal Nerve

The inferior rectal (inferior hemorrhoidal) supplies the external sphincter ani, assists in supplying the levator ani, and provides cutaneous innervation for the skin around the anus and the mucosal lining of the anal canal below the pecten.

Perineal Nerve

The perineal branch divides into posterior scrotal or labial cutaneous branches and deep muscular branches. The latter supply the muscles of the superficial perineal pouch and deep perineal pouch (the urogenital diaphragm).

Dorsal Genital Nerve of the Penis or Clitoris

The dorsal nerve of the penis supplies the glans, the prepuce, and the skin of the penis/spongy urethra in the male and the clitoris in the female.

The territories the pudendal nerve supplies are pelvic, pudendal, deep perineal pouch, dorsum of penis or clitoris, and gluteal. The gluteal territory, however, is disputed by several anatomists, since the nerve only passes through the area.

Cutaneous Nerves of Urogenital Triangle

The cutaneous nerves of the urogenital triangle (Fig. 28-28 A&B) supply the following areas:


Ilioinguinal nerve (L1): anterior 1/3 of the labia majora/ scrotum

Dorsal nerve: skin of the clitoris/penis

Perineal branch of posterior cutaneous nerve of thigh: lateral, posterior 2/3 of labia majora/scrotum. It may replace the pudendal nerve in much of the cutaneous supply.

Labial/scrotal branches of perineal branch of pudendal nerve: medial, posterior 2/3 of labia majora/scrotum

L1: dorsal aspect of root of penis

S2-S3: areas distal to axial line, penile skin, and adjoining scrotum

Fig. 28-28.

Cutaneous nerves of the perineum. A, Male; B, Female. (Modified from Toldt C, Hochstetter F. Anatomischer Atlas. Munich: Urban & Schwarzenberg, 1976; with permission.)

Sciatic Nerve

The sciatic nerve (L4-S3) is the largest nerve of the body. The pudendal and sciatic nerves are the terminal branches of the sacral plexus.

The path of the sciatic nerve (Fig. 28-1, Fig. 28-21, Fig. 28-23) is described below.


It emerges from the greater sciatic foramen beneath the lower border of the piriformis muscle and under the gluteus maximus

It crosses the posterior surface of the ischium and descends on the adductor magnus, deep to the long head of the biceps femoris

Near the ischial tuberosity, it provides motor branches for the long head of the biceps femoris, the semitendinosus, the semimembranosus, and the distal part of the adductor magnus muscles

At midthigh (variably), it divides into the tibial (L4-S3) and common fibular (peroneal) nerves (L4-S2)

The tibial division of the sciatic nerve supplies the three longer components of the hamstring muscles (long head of biceps, semimembranosus, semitendinosus) and also the adductor magnus (the superior part of which is innervated by the obturator nerve)

The common peroneal division innervates only the short head of the biceps in its course in the thigh, but supplies all of the musculature and most of the cutaneous supply to the leg and foot

Segmental Cutaneous Supply of the Lower Limb


L1-L3 supplies the anterior thigh from above down, including the anterior scrotum (vulva)

L4 supplies the leg and foot medially

L5 supplies:


– Leg anterolaterally

– Dorsum and sole of the foot

S1 supplies:


– Band of skin on the posterior thigh surface (by the posterior femoral cutaneous nerve)

– Posterior side of the calf (medial and lateral sural cutaneous nerves)

– Lateral side of the foot (sural nerve and lateral cutaneous nerve of the foot)

S2 contributes sensory fibers to the posterior surface of the thigh and leg

S3 and S4 supply the skin of the buttocks and lateral aspects of the perineum (including the posterior scrotum or vulva) by the perineal branch of the posterior femoral cutaneous nerve


L1 supplies the anterior scrotum or vulva. S3 supplies the posterior scrotum or vulva.

NOTE: In some individuals, most of the sensory fibers to the perineum are derived from the posterior femoral cutaneous nerve. In such cases, pudendal nerve block may not be totally successful in achieving anesthesia.

A little aid for memory follows:


5 supplies 1, and 1 supplies 5 (meaning that L5 supplies the 1st toe and S1 supplies the 5th toe)

Myotomes of the Lower Limb

In general, the motor supply to the lower limb can be summarized as follows. Remember that the large muscles of the lower limb are, in almost every case, supplied by two or more spinal nerve levels.


L1, L2, hip flexion (iliopsoas)

L2, L3 [anterior divisions], adductor musculature

L2, L3 [posterior divisions], quadriceps femoris muscles, sartorius (L4 carries the sensory limb of the patellar reflex)

L4, foot inversion (tibialis anterior and posterior)

L4, L5, foot dorsiflexion (extensores hallucis and digitorum)

L5, foot dorsiflexion and inversion; great toe extension (extensor hallucis longus); hip abduction (gluteus medius, minimus); knee flexion (long hamstrings)

S1, foot eversion (peroneal musculature); hip extension (gluteus maximus); knee flexion (short head of biceps femoris); plantar flexion of the foot (gastrocnemius, soleus)

S2, toe pushoff (flexor hallucis and digitorum longus)

S2, S3, intrinsic muscles of the sole of the foot

The following statements are usually true regarding pelvic sensation.


Pain from upper pelvic viscera (ovaries, uterine fundus and body, most of the bladder) is carried by sympathetic routes. Pain from lower visceral elements (cervix, upper vagina, vesical trigone) is carried by the pelvic splanchnic nerves. Clinical data indicate that there can be considerable variation in the pain pathways between individual patients.

Sensations of bladder distention are carried by pelvic splanchnic nerves (nervi erigentes). Bladder pain, especially from its lower segment, is transmitted by the sacral parasympathetics and not through the hypogastric plexus.

Sensations of rectal distention are carried by pelvic splanchnic nerves (nervi erigentes). Rectal pain is carried by sacral nerves.

Pain of the body of the uterus is carried by the hypogastric nerve, lumbar splanchnic nerves, and sympathetic chains. The cell bodies are found in the dorsal root ganglia of T11-L2 spinal nerves.

Pain fibers from the cervix travel in the pelvic splanchnic nerves and have their cell bodies in the dorsal root ganglia of S2, S3 and S4.

Pain from inflamed viscera is due to excessive dilation or swelling, muscle spasm, tension of the mesenteric folds, or involvement of the parietal peritoneum.

Intensity of pain perception indicates the nerve carrying the pain. Visceral nerve branches carry a dull perceived pain from above the anal pecten. Somatic nerve branches of the pudendal nerve carry sharp, precisely located pain from the pecten outward. Robert et al.28 report on the role of the pudendal nerve in perineal pain. They propose treatment by infiltrations at the level of the ischial spine or at the pudendal canal, and by surgery by a transgluteal route.

Presacral resection for pain is disappointing and unpredictable in results.

Fifth Surgicoanatomic Layer: Muscles

The pelvic muscles (Fig. 28-2) can be divided into lateral pelvic muscles (piriformis and obturator internus) and the muscles of the pelvic diaphragm. First we consider the muscles of the lateral pelvic wall. Muscles of the pelvic diaphragm are considered in the following section on the pelvic floor.

The following paragraphs consider place of origin, insertion, nerve supply, and action of the lateral pelvic muscles (piriformis and obturator internus).


The piriformis muscle:


Is a part of the lateral pelvic wall

Originates from the anterior sacrum, greater sciatic notch, and sacrotuberous ligament

Inserts at the upper border of the greater trochanter

Is supplied by the L5-S2 nerves

Rotates the extended thigh laterally and abducts the flexed thigh


Within the pelvis, the piriformis is related to the rectum, sacral plexus, branches of the internal iliac vessels and, inferiorly, the coccygeus muscle. Outside the pelvis, the piriformis is related to the posterior surface of the ischium, the capsule of the hip joint, and the gluteus maximus (Figs. 28-1 and 28-8).

Obturator Internus and Obturator Hernia

The obturator internus:


Lies partly within the pelvis and partly posterior to the hip joint

Originates on the internal surface of the ilium, pubic bone and ischium, ischiopubic rami, and inner surface of the obturator membrane

Inserts at the medial surface of the greater trochanter

Is supplied by the L5-S1 nerves

Rotates the extended thigh laterally and abducts the flexed thigh


The pelvic surface of the obturator internus forms the lateral boundary of the ischioanal fossa of the perineum. This boundary consists of fat-filled, pyramid-shapes on either side of the anus (Fig. 28-2B). Outside the pelvis, the obturator internus muscle is first joined by the superior and inferior gemelli, following their origin from the margin of the lesser sciatic foramen; thereafter, it is covered by the gluteus maximus and crossed by the sciatic nerve (Fig. 28-2).

The tendinous arch of the levator ani muscle, a specialization of the internal fascia of the obturator muscle, follows a line from the ischial spine to the posterior aspect of the body of the pubic bone. This fascial thickening gives origin to the lateral part of the pubococcygeus muscle and the entire iliococcygeus muscle. Along its path, the arcus tendineus of the levator ani is very closely related anteriorly to the proximal urethra and the neck of the urinary bladder. Klutke and Siegel29 correctly identify the arcus tendineus as a fascial ring at the pelvic outlet that laterally secures the pelvic floor and several ligaments (Fig. 28-29).

Fig. 28-29.

Pelvic floor with levator muscle attached laterally to arcus tendineus (abdominal view). (Modified from the American Urological Association, Inc. The Anatomy of Stress Incontinence. AUA Update Series, Lesson 39, Volume IX, 1990, p. 306; with permission.)

NOTE: Part of the lateral wall of the false pelvis is formed by the iliacus muscle, which completely fills the iliac fossa. We do not consider the psoas major and minor muscles as musculature belonging to the lateral pelvic wall. Their presence on the bony rim of the pelvic sidewall does effectively deepen the true pelvic cavity, as can be appreciated in sectional imaging. We believe that, for all practical purposes, these muscles belong to the posterior abdominal wall and lower limb. The only relationship between the psoas and iliacus muscles is that the tendon of the psoas major unites with the tendon of the iliac close to and above the inguinal ligament. The tendon of the combined iliopsoas then passes underneath the ligament and inserts into the lesser trochanter of the femur.

An obturator hernia is an abnormal protrusion of preperitoneal fat or an intestinal loop through the obturator canal. It characteristically affects the right side of middle-aged women. Its relation to groin hernia is seen in Fig. 28-30A.

Fig. 28-30.

Surgical anatomy of the obturator region. A, Lateral view of the right side of the pelvis showing the sites of inguinal, femoral, and obturator hernias. B, View of the medial wall of the male pelvis showing the obturator canal and structures passing through it. C, Diagrammatic coronal section of the lateral wall of the male pelvis showing the relation of obturator nerve, artery, and vein to other pelvic structures. D, The course and distribution of the right obturator nerve. E, Diagram of long section of the upper thigh through the obturator foramen showing the potential paths of obturator hernia. The hernia may follow the anterior or posterior division of the nerve. F, As it emerges through the obturator canal, the obturator artery divides to form an arterial ring around the obturator foramen. (A, D, F from Skandalakis JE, Gray SW. Obturator hernia. In Nyhus LM, Condon RE (eds). Hernia (4th ed). Philadelphia: Lippincott, 1995; with permission. B, C, E from Gray SW, Skandalakis JE, Soria RE, Rowe JS Jr. Strangulated obturator hernia. Surgery 1974;75:20-27; with permission.)

The obturator region is bounded superiorly by the superior ramus of the pubic bone, laterally by the hip joint and the shaft of the femur, medially by the pubic arch, the perineum, and the gracilis muscle, and inferiorly by the insertion of the adductor magnus on the adductor tubercle of the femur.

The obturator foramen is the largest bony foramen in the body and is formed by the rami of the ischium and pubis. It lies inferior to the acetabulum on the anterolateral wall of the pelvis. Except for a small area, the obturator canal, the foramen is closed by the obturator membrane. Fibers of the membrane are continuous with the periosteum of the surrounding bones and with the tendons of the internal and external obturator muscles. Embryologically, the foramen and its membrane represent an area of potential bone formation that never proceeds to completion. In this sense the obturator foramen is a lacuna and the obturator canal is the true foramen.

The obturator canal is a tunnel 2 to 3 cm long beginning in the pelvis at the defect in the obturator membrane. It passes obliquely downward to end outside the pelvis in the obturator region of the thigh. The canal is bounded above and laterally by the obturator groove of the pubis and inferiorly by the free edge of the obturator membrane and the internal and external obturator muscles. Through this canal pass the obturator artery, vein, and nerve (Fig. 28-30A&B), and the hernial sac, if an obturator hernia is present.

The obturator nerve is usually superior to the artery and vein (Fig. 28-30C). The nerve separates into anterior and posterior divisions as it leaves the canal (Fig. 28-30D). The hernial sac may follow either division of the nerve (Fig. 28-30E). The obturator artery divides to form an arterial ring around the foramen (Fig. 28-30F). In the majority of cases, this artery provides the artery to the head of the femur.

The approach for the repair of an obturator hernia may be abdominal, retropubic, obturator, inguinal, laparoscopic, or a combination. Decision as to the approach depends upon whether there is a certain diagnosis. With certain diagnosis, we advise a lower suprapubic transverse incision. Without certain diagnosis, we advise lower midine incision.

Surgical Considerations


The retropubic space of Retzius communicates with the space occupied by areolar tissue in front of and to the sides of the bladder but not behind it. The retropubic space is also indirectly continuous with an inferior abdominal wall area, the space of Bogros.

We quote from Killackey12 on female colorectal cancer surgery:

The most important principle of curative surgical therapy is total resection of the mesorectum with careful, deliberate, hemostatic dissection along parietal pelvic fascia. …. To completely mobilize the rectum and treat most midrectal cancers, the rectovaginal septum must be dissected creating a rectovaginal space down to the pelvic floor. … The boundaries of the rectovaginal space are: the pouch of Douglas (base of the cul de sac) cranially; perineal body caudally; and the pararectal spaces laterally.


The neck of the bladder or upper part of the prostate is attached to the distal part of the symphysis pubis by a cordlike ligament, a specialized thickening of the endopelvic fascia. This forms the puboprostatic or pubovesical ligaments.

The pelvic splanchnic nerves are contained within a fine areolar fold, located at each side of the retrorectal space. It is essential in pelvic surgery to avoid injuring these nerves. An injury can cause bladder and rectal physiological impairment, and in the male, problems with erection.

The presacral venous plexus can produce bleeding during pelvic surgery, especially with mobilization of the posterior rectal wall. The bleeding can be controlled with a tack or by using muscular plugs.

Qinyao et al.30 stated that large ventral neural foramina, 2 mm to 5 mm in diameter, were located in the 3rd, 4th, and 5th segments of the sacral body in 16 percent of their cases. The walls of the presacral veins are fixed to the sacral periosteum and the presacral fascia. In an effort to perform a better cancer operation, the surgeon removes the presacral fascia and sometimes the sacral periosteum. This can produce copious venous bleeding that is difficult to control because of the retraction of the veins within the foramina.

The presacral fascia is part of the parietal fascia. Because of its paucity of lymphatics, it is not necessary to remove it. Invasion of the fascia by cancer is not curable.

The obturator test is used to diagnose appendicitis. If the acute appendix is located over the pelvic brim, and if stretching the obturator internus muscle by flexing and rotating the thigh inward results in pain, the diagnosis is confirmed. The pain is due to inflamed fascia and peritoneum.

Damage to the sciatic nerve creates paralysis of the hamstring muscles and all the muscles of the leg and foot. In gynecologic surgery, footdrop deformity can occur as a complication of injury to the fibers of the common peroneal division of the sciatic nerve within the true pelvis.

Other nerves subject to injury by direct manipulation, retraction, or inadvertent clamping or laceration are:


– Genitofemoral (lumboinguinal)

– Ilioinguinal

– Lateral cutaneous of thigh

– Intermediate cutaneous of thigh

– Medial cutaneous of thigh

– Iliohypogastric

– Obturator

– Femoral

Compression neuropathies must be considered in the differential diagnosis of sciatic pain. In the most common anatomic arrangement, the entire sciatic nerve passes inferior to the piriformis muscle. In somewhat less than 10 percent of individuals, the common fibular (common peroneal) division of the sciatic nerve passes through the piriformis muscle. In rarer cases, the whole sciatic nerve passes through the piriformis. Either variation can result in “piriformis entrapment,” causing gluteal pain and/or sciatica, described below. Even less frequently, the peroneal division leaves the pelvis superior to the piriformis, and the tibial division of the sciatic nerve pierces the muscle.

Recognized more often in recent years as a cause of sciatic pain, piriformis syndrome can occur when the peroneal division of the sciatic nerve is compressed by contractions of the piriformis muscle. Piriformis syndrome (entrapment of the sciatic nerve on the sharp lower edge of the greater sciatic notch) may cause symptoms along the course and distribution of its component parts. Patients with piriformis syndrome complain of pain and/ or paresthesia in the distribution of the sciatic nerve. These complaints can seem almost identical to those experienced with compression of the S1 nerve root by vertebral disk herniation at the level of the fifth lumbar vertebra. The symptomatology can be considerably greater than this, depending upon the nature of the entrapment and its severity. Complete nerve palsy is rare.

Electromyography and nerve conduction studies are needed to confirm the diagnosis of piriformis entrapment. Look for normal activity in the gluteus maximus, gluteus medius, gluteus minimis, and tensor fasciae latae muscles, and abnormalities in innervation below this. Prescribe conservative measures (physical therapy, bed rest, antiinflammatory analgesics, and muscle relaxants) initially. If these fail, and if the diagnosis of piriformis syndrome has been substantiated, try division of one of the heads of origin of the piriformis muscle and operative neurolysis.31

The fascia propria of the rectum is an enigmatic anatomic entity (Fig. 28-31). It envelops the rectum and its vessels, lymphatics, and nerves, but does not invest the rectal wall. It is located anterior to the retrorectal space. The so-called rectal mesentery (or mesorectum or fatty tissue) at the posterior part of the rectum is enclosed by the fascia propria.

Many elements of the pelvic plexus are located below the uterine vessels in the cardinal ligament. Numerous visceral nerve fibers from the hypogastric plexus do, however, surround the ureter and the uterine vessels. If the nerves to the uterus are severed, it is usually in association with removal of the uterus, so that the nerve loss is of no consequence. Therefore, significant injury to the plexus during hysterectomy (not radical) is an uncommon sequela.

Most rectoceles are caused by obstetrical trauma. If Denonvilliers’ fascia is torn from the perineal body, a low rectocele can form. If the fascia is torn at higher levels, midvaginal or high vaginal rectoceles or enteroceles can result, especially if the rectovaginal septum separates from its central attachments to the uterosacral ligaments. An enterocele usually consists of herniating peritoneum from the cul-de-sac, with small intestine within the peritoneal sac. Treatment must include restoration of the integrity of the rectovaginal septum.

Operative trauma is a rare cause of rectovaginal fistula. According to Killackey,12 with procedures that manipulate the rectovaginal space, such as vaginal hysterectomy, rectocele and vaginal vault prolapse repair, low anterior resection, ileal pouch-anal anastomosis and anorectal surgery, there is a 1%-2% possibility of rectovaginal fistula.

Brunschwig and Walsh32 found it possible to remove large segments of both the internal iliac vein and the common iliac vein in individuals with laterally extended malignant neoplasms.

Batson33 emphasized that blood-borne infections or malignant cells from pelvic organs reach the spinal column and brain without passing through the lungs (as we noted earlier in the chapter).

When treating cancer involving the anterior rectal wall, the fascia propria and the proximal part of Denonvilliers’ fascia should be removed.

When treating cancer involving the posterior rectal wall, all the fatty tissue should be removed, including the fascia propria. Do not remove the presacral fascia. Also, the posterior part of the pelvic plexus and the pelvic parasympathetics are close to the anterolateral part of the distal colon. Thus, if the cancer is located at the posterior rectal wall, the dissection should be close to the anterolateral aspect of the rectum. The nerves, however, should be sacrificed for a good cancer operation.

Fig. 28-31.

Male pelvis showing fascia in front of and behind rectum (schematic sagittal section). Dotted lines represent paths of incisions in abdominoperineal resection for cancer. Note the incision of anterior peritoneum in front of fascia of Denonvilliers. Fascia of Denonvilliers is incised lower down, opposite seminal vesicles. Rectosacral fascia is incised posteriorly, disconnecting rectum from hollow of sacrum. (Modified from Church JM, Raudkivi PJ, Hill GL. The surgical anatomy of the rectum: A review with particular relevance to the hazards of rectal mobilization. Int J Colorect Dis 1987;2:158-166; with permission.)

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Anatomic Complications

The anatomic complications of the pelvic wall are the complications of surgery of the several anatomic entities related to the lateral pelvic wall.

We appreciate the concise wisdom of Wagner and Russo36:

Iatrogenic injury has become the most common etiology of genitourinary trauma. Careful attention to detail during the pre-operative and intra-operative periods is critical in avoiding these vexing complications. Unfortunately, the proximity of the pelvic organs along with disease processes will continue to result in some untoward urologic complications. The complexity of these complications mandates a multidisciplinary approach with the pelvic surgeon and urologist leading the team.

Pelvic Floor

Surgical Anatomy

Form, Function, and Development

The floor of the pelvis is composed of musculature, erectile tissues, and connective tissues (including the perineal membrane) of the perineum below and the pelvic diaphragm and its superior and inferior fasciae above.

Almost by convention, the floor of the pelvis is usually described with the organs that occupy the cavity of the true pelvis. The perineum is presented separately, as though it is a totally separate entity. This, we believe, adds to the confusion experienced by the student, the practitioner, and the anatomist in attempting to understand the anatomy and many of the clinical problems of the pelvis.

In reality, the musculofascial pelvic floor and the entities of the perineum are very closely related embryologically, structurally, and functionally. The various elements that support the pelvic viscera and participate in their functions are presented here together, artificially separable, but interdependent by development and design.

The integrity of the floor of the pelvic basin is dependent upon the proper architectural form and vitality of both the levator ani and urogenital structures. This becomes exceedingly clear when one comes to understand the significance of the true and proper orientation of the bony pelvis in humans in the standing position.

When one stands upright, the anterior superior iliac spines and the pubic tubercles lie in the same vertical plane (Fig. 28-32). Although the truth of this is acknowledged in most modern anatomy textbooks, illustrations of the bony pelvis in many of the same reference texts exhibit an error of almost 60° in its orientation, often labeling the true anterior view as one from a superior point of view (Fig. 28-33).2

Fig. 28-32.

Properly oriented hip bone (os coxae) (side view). Top part contacts black vertical bar at anterior superior iliac spine; bottom part contacts at pubic tubercle. Smaller black bars mark approximate boundaries between bones of os coxae. (Modified from Stromberg MW, Williams DJ. The misrepresentation of the human pelvis. J Biocommun 1993;20:14-28; with permission.)

Fig. 28-33.

Upper, Commonly presented, but incorrect, “front view” of bony pelvis, rotated about 60° to 75° from proper position. Lower, Similar incorrect view of bony pelvis, originally published in 1801. (Modified from Stromberg MW, Williams DJ. The misrepresentation of the human pelvis. J Biocommun 1993; 20:14-28; with permission.)

Because of the relatively vertical orientation of the pelvic inlet, with the pubic symphysis and much of the ventral surface of the sacrum oriented essentially downward, the long axis of the symphysis slopes downward at an approximate angle of 30° to the horizontal from anterior to posterior in the female, slightly more than this in the male (Fig. 28-34). The ischiopubic ramus essentially parallels the ground. Thus, much of the pressure and the weight of organs within the abdominopelvic cavity is directed toward the region of the urogenital triangle, the interval between the inferior rami of the pubic bones. Because of the pelvic orientation in humans, the urogenital muscular and fascial elements interconnecting the ischiopubic rami undergird the musculofascial floor of the pelvis, the pelvic diaphragm, providing essential assistance to its role in support and its multiple roles in pelvic visceral functions.

Fig. 28-34.

Properly oriented bony pelvis with proximal femora attached (front view). Note that most of sacrum recedes from observer. Compare to Fig 28-33. (Modified from Stromberg MW, Williams DJ. The misrepresentation of the human pelvis. J Biocommun 1993;20:14-28; with permission.)

The integrity of the support of the pelvic organs is dependent upon the following complex of structural features:


Extraperitoneal smooth muscle and associated visceral ligaments passing from the pelvic sidewalls to the viscera

Musculature, aponeurotic tissues, and fasciae of the pelvic diaphragm

Muscles, cavernous tissues, and fasciae of the urogenital triangle, including the perineal membrane

The first of these structural support systems is well described by Power,37 and is elucidated elsewhere in this text in the chapter on the female genital system. The third of these structures, the urogenital triangle, will be considered later in this chapter under the section on the perineum. The pelvic diaphragm is reviewed in the following paragraphs.

Pelvic Diaphragm

The pelvic diaphragm (Fig. 28-35, Fig. 28-36, Fig. 28-37) provides a musculofascial floor for the true pelvis. This floor is complete except for the midline openings between the two halves of the diaphragm. These openings are the urogenital hiatus and the rectal hiatus.

Fig. 28-35.

Coronal section of male pelvis illustrating main part of funnel-shaped pelvic diaphragm formed mainly by two levator ani muscles. Pelvic diaphragm forms floor of abdominal and pelvic cavities and consists of paired levator ani and coccygeus muscles with their superior and inferior fasciae. Rectum is anchored to pelvic diaphragm in middle (see Fig. 28-41). Only pelvic diaphragm (levator ani portion) intervenes between ischioanal fossa and retropubic space. (Modified from Moore KL. Clinically Oriented Anatomy (2nd ed). Baltimore: Williams & Wilkins, 1985; with permission.)

Fig. 28-36.

Muscles of female pelvic diaphragm. A, Seen from above. B, Seen from below. (Modified from Gray SW, Skandalakis JE. Atlas of Surgical Anatomy for General Surgeons. Baltimore: Williams & Wilkins, 1985; with permission.)

Fig. 28-37.

Muscles of male pelvic diaphragm. A, Seen from above. B, Seen from below. (A, Modified from Christensen JB, Telford IR. Synopsis of Gross Anatomy (5th ed). Philadelphia: JB Lippincott, 1988; with permission. B, Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair. Pearl River NY: Parthenon, 1996; with permission.)

The rectum, urethra, and vagina pass together with fascia of the levator ani through the pelvic diaphragm. The diaphragm is composed of two paired muscles, the levator ani and coccygeus.

Anteriorly, between the inferior pubic rami, where the stress upon the pelvic floor is greatest in the upright posture, the floor is reinforced by the underlying urethrogenital complex of structures, including the so-called urogenital diaphragm.

The muscles of the pelvic diaphragm originate in the spine of the ischium, the white line (arcus tendineus) of the obturator fascia, and the body of the pubis. These muscles insert into the coccyx, the anococcygeal raphe, the perineal body, and the midline viscera (Fig. 28-38). The musculature of the pelvic diaphragm produces a gutterlike formation that slopes forward and downward.

Fig. 28-38.

Pelvic diaphragm from below. Levator ani composed of three muscles: puborectalis, pubococcygeus, and iliococcygeus. (Modified from Skandalakis JE, Gray SW, Rowe JS Jr. Anatomical Complications in General Surgery. New York: McGraw-Hill, 1983; with permission.)

Levator Ani

The levator ani can be considered to be made up of three contributing muscular entities: iliococcygeus, pubococcygeus, and puborectalis (Fig. 28-38). This last component is essential to maintaining rectal continence. Shafik38 considers the puborectalis to be part of the external sphincter and not a part of the levator ani.


The posterior edge of the pubococcygeus is in some cases separated by a narrow aponeurosis from the thinner and more aponeurotic iliococcygeus. In other cases they are continuous.

The iliococcygeus arises from the arcus tendineus levator ani, the more or less apparent specialization of the fascia of the internal obturator and fascia of the levator ani. The iliococcygeus inserts in the midline raphe (Fig. 28-38) and upon the coccyx.


The lateral borders of the urogenital hiatus of the pelvic diaphragm are formed by the medial borders of the pubococcygeus; the puborectalis takes a more lateral course from its origin.

In a study of histologic sections and grossly dissected specimens, Delancey and Starr39 note that smooth muscle, collagen, and elastic fibers of the vaginal wall and paraurethral tissues interdigitate directly with the most medial muscle fibers of the levator ani. This occurs in the vicinity of the proximal part of the urethra. This strong attachment extends from the level of the entrance of the ureters into the bladder inferiorly to the urogenital diaphragm. They conclude that the inseparable nature of the vagina and lower urethra and the lateral attachments to the levator ani make it possible for the medial levator ani muscle to play a role in controlling the position of the vesical neck, and thus perhaps in voiding and continence. Mostwin40 observes that disruption of the attachments of the pubococcygeus to the vaginal wall can result in herniation, with accompanying secondary posterior bladder descent.

In our dissections, we observed the strong intermingling of the most anterior and medial part of the pubococcygeus with the superolateral aspect of the vagina and the paraurethral musculature in the female and the prostatic capsule in the male. In both male and female, some fibers pass deeply around these structures to insert into the perineal body. External to this lamina of fibers from the pubococcygeus, another fleshy muscular band arises partially from the pubic bone and partially from the fascia of the obturator internus. It passes behind the rectum to become continuous with fibers from the opposite side. As noted by Oelrich41 in studies of the gorilla and humans, the pubococcygeus has no attachment to the coccyx.

Levator Plate

The striated musculature between the coccyx and the rectum, including the iliococcygeus and the posterior part of the pubococcygeus, forms the “levator plate.” The strength of the levator plate and its degree of angulation with the horizontal plane from the coccyx to the rectum are both of importance in maintaining fecal continence.

The levator plate is also responsible for prevention of prolapse of the upper vagina, the uterus, and the rectum. With coughing, laughing, or straining, the vertical pressures exerted by the Valsalva maneuver bear directly upon these organs. The normal levator plate ascends to meet the organs, impinging upon them and preventing their prolapse.


The puborectalis arises from the lower posterior surface of the pubic bone. It is lateral and external to the pubovaginalis (levator prostatae) and pubococcygeus. Also, some of its deeper fibers take origin from fibrous tissue intervening between it and the sphincter urethrae muscle.42 This gives further credence to the possible influence of contraction of the levator ani muscle upon urethral function and continence. Fibers from the left and right puborectalis muscles pass posteriorly. They then join posterior to the rectum, forming a well-defined sling (Fig. 28-39). Here, they blend with and pass external to the more cranial part of the deep external sphincter.

Fig. 28-39.

Floor of pelvis seen from above showing levatores ani. Inset: How the anorectal junction is angulated by the sling formed by the puborectalis muscles. (Modified from McGregor AL, DuPlessis DJ. A Synopsis of Surgical Anatomy (10th ed). Baltimore: Williams & Wilkins, 1969; with permission.)

The puborectalis forms the so-called anorectal ring with the superficial and deep parts of the external sphincter and the proximal part of the internal sphincter. This ring can be palpated. Because cutting through it will produce anal incontinence, it must be identified and protected during surgical procedures. Further details of the external sphincter will be discussed with the morphology of the anal canal.


Another contributor to the pelvic diaphragm musculature is the coccygeus (Fig. 28-39). It arises from the spine of the ischium and the pelvic surface of the sacrospinous ligament, overlapping it somewhat. The coccygeus inserts upon the lateral aspects of the lower two sacral vertebrae and upon the upper two coccygeal vertebrae.

The funnel shape of the pelvic floor and anal canal is uniquely developed to provide discriminatory continence of gas, liquid, and solid. Many of the physiologic factors involved in this discrimination and control are poorly understood.43 It has become conventional to speak of two diaphragms associated with the pelvic outlet, the pelvic diaphragm and the urogenital diaphragm. In fact, these structures are more closely related anatomically and functionally than most sources recognize.

In embryologic development, the sphincter urethrae muscle and the other muscles of the perineum, including the external anal sphincter, arise from the cloacal sphincter and form an accessory pelvic diaphragm.44 The levator ani arises from the caudal musculature. In lower animals, the caudal musculature is responsible for movements of the tail. It is modified in its human form to provide support functions.45 Levi et al.46 emphasize that the puborectalis is, indeed, a part of the levator ani, citing its common embryologic origin with the pubococcygeus and iliococcygeus muscles. On the other hand, Cherry and Rothenberger43 state that the puborectalis is anatomically, neurologically, and functionally merged with the deep portion of the external sphincter ani muscle.

Innervation of the Pelvic Diaphragm

The pelvic diaphragm receives nerve supply on its pelvic surface by the nerve to the levator ani, which arises from the ventral primary ramus of S4 or S5. A perineal branch arising either from this nerve or directly from the ventral primary ramus of S4 may pierce the coccygeus muscle, supply it, and then further supply the external sphincter ani. Additionally, the nerve to the levator ani may provide origin for a branch that joins the pudendal nerve at the entrance to the pudendal canal.

Observations Regarding the Pelvic Floor


The pelvic diaphragm prevents evisceration and never prolapses. Together with the anal sphincters, the anococcygeal ligament, and the perineal body, it supports the rectum and anal canal (Fig. 28-40).

Several slings form and support the pelvic floor. In the male, a sling forms around the prostate (levator prostatae or prostate levator) and passes behind it in a U-like formation. Both limbs insert into the perineal body. In the female, a sling at the internal sphincter of the vagina (pubovaginalis) passes behind the vagina in a U-like formation to insert into the perineal body. This “sphincter” of the pelvic floor should not be confused with the sphincter of the introitus (sphincter urethrovaginalis and bulbospongiosus muscles). In both male and female, the puborectalis (see Fig. 28-39 inset) is the most important sling.

The puborectalis forms a sling that is responsible for the closing of the anorectal canal.

The pelvic floor slopes downward and forward to receive the lowest part of the fetus (Fig. 28-41).

The passive stretching and active contraction of the iliococcygeus participates in the mechanisms of defecation, micturition, and parturition.

The levator ani, arcus tendineus fascia pelvis, and visceral fascia collaborate to create the integrity of the pelvic floor.

The obturator nerve supplies the adductor muscles of the thigh. It is the most important nerve to protect in the superolateral wall of the true pelvis (see Fig. 28-30D).

It is not known what nerve(s) innervates the visceral peritoneum.

The pudendal nerve and internal pudendal artery and vein provide neural and vascular supply for the perineum and, in part, for the pelvic floor.

The internal iliac vessels, the hypogastric nerve, and the pelvic splanchnic nerves provide the blood supply and innervation to the rectum and urinary bladder.

The pelvic diaphragm musculature, its aponeurotic tissues, and its fascial coverings provide the fibromuscular pelvic floor and include the levator ani and coccygeus muscles. The endopelvic fascial lining of the muscles (pelvic surface) is essentially continuous with the transversalis fascial layer of the abdominal cavity.

Fig. 28-40.

Female pelvic diaphragm. A, Its formation by several muscles, from below. B, The perineal body (light gray) in sagittal section. It is larger, and contains more muscle, in the female than in the male. (A, Modified from Gray SW, Skandalakis JE. Atlas of Surgical Anatomy for General Surgeons. Baltimore: Williams & Wilkins, 1985; B, Modified from Hollinshead WH. Anatomy for Surgeons, Vol 2. New York: Hoeber-Harper, 1956; with permission.)

Fig. 28-41.

Female pelvis (paramedian section). (Modified from Gray SW, Skandalakis JE. Atlas of Surgical Anatomy for General Surgeons. Baltimore: Williams & Wilkins, 1985; with permission.)

Structures of the Fasciae of the Pelvic Floor

The fasciae of the pelvis were described earlier in this chapter in discussing the pelvic sidewalls. We now relate some of the points discussed there to the structures of the pelvic floor.

The three different forms of fasciae associated with the pelvic floor are the parietal, visceral, and diaphragmatic fasciae. They are discussed below.

Parietal Fascia

The parietal portion of the pelvic fascia is in large measure the fascia of the obturator internus, piriformis, and pelvic diaphragm muscles because it covers these muscles during its journey to reach and attach to the bones and ligaments of the pelvic outlet. The fascia of the obturator internus is seemingly interrupted within the pelvis by the narrow band of origin of the levator ani. This fascia, however, continues below that origin, thereby forming the lateral boundaries of the perineum below the floor of the pelvis. To be more specific, this fascia is responsible for the formation of Alcock’s canal (Fig. 28-3) at the lateral wall of the ischioanal fossa where it covers the obturator internus muscle.

Visceral Fascia

The visceral portion of the pelvic fascia is in continuity with the endopelvic connective tissues that intervene between the peritoneum and the parietal fascia of the pelvic sidewall and floor. The visceral fascia invests almost all of the pelvic surfaces of the organs within the pelvis. The possible exception to this may be parts of the fundus of the uterus and bladder. The visceral fascia is also continuous with the endopelvic connective tissue that provides connective tissue sheaths for the nerves and vessels supplying the organs. In addition, the coverings of the organs, nerves, and vessels are particularly reinforced by the following supporting structures:


“Pillars” of the rectum and bladder

Uterosacral and lateral cervical (Mackenrodt) ligaments of the uterus

Rectovaginal (rectoprostatic) septum

Arcus tendineus fascia pelvis

Pubovesical fascial covering joining the bladder, vagina, and cervix

Extrinsic prostatic capsule

Diaphragmatic Fascia

The diaphragmatic fascia covers the superior surface (supraanal fascia) and the inferior surface (infraanal fascia) of the pelvic diaphragm. The diaphragmatic fascia is commonly accepted to be related to the superior fascia of the urogenital diaphragm. But this point should be understood in the context of the following section on the perineum.

The superior layer of the urogenital diaphragm is continuous (at least at its peripheral edges) with the pelvic parietal fascia that clothes the superior surface of the pelvic diaphragm. The inferior fascia (perineal membrane) is perhaps a different embryologic entity. However, it is reasonable that the envelope of the urogenital diaphragm could be of endopelvic origin. From a surgical standpoint this embryologic problem, if there is one, does not affect the functioning of the urogenital diaphragm in health and disease.

Perineal Body (Center) and Perineal Hernia

The perineal body (center) (see Fig. 28-19, Fig. 28-38 and Fig. 28-40A&B) in the male represents the central tendinous point, a bolus of tissue between the anus and bulb. In the female it is the “perineum” of the gynecologist, a fibromuscular mass of tissue between the anus and vagina.

The perineal body, located under the pelvic floor, is formed by the attachments of several muscles. These include the following:


Superficial transverse perineus


Sphincter urethrae in the male

Sphincter urethrovaginalis and deep transverse perineus muscles in the female

Superficial part of the external anal sphincter

Levator prostatae and pubovaginalis of the levator ani

The perineal body is a midline landmark between the anterior and posterior triangles of the perineum. It gives some support to the levator ani muscle and thus to the pelvic organs.

A perineal hernia (Fig. 28-42) is the protrusion of a viscus through the floor of the pelvis (pelvic diaphragm) into the perineum. A hernial sac is present. The hernia may be primary, or it may be secondary to pelvic surgery. Only primary hernias are of concern here.

Fig. 28-42.

The female perineum. A, The female perineum seen from below showing possible sites of perineal hernias. A primary perineal hernia may occur anterior or posterior to the superficial transverse perineus muscle. An anterior hernia protrudes through the urogenital diaphragm into the triangle formed by the bulbospongiosus muscle medially, the ischiocavernosus muscle laterally, and the superficial transverse perineus muscle inferiorly. Anterior hernias occur only in females. A posterior perineal hernia may emerge between component muscle bundles of levator ani muscle or between that muscle and coccygeus muscle midway between the rectum and the ischial tuberosity. B, Boundaries of the perineum seen from above. This diamond-shaped area can be divided by a line connecting the ischial tuberosities into an anterior or urogenital triangle and a posterior or anal triangle. (Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair. Pearl River NY: Parthenon, 1996; with permission.)

Perineal hernia is among the rarest of human hernias. Unlike inguinal hernia, which appears to be related to the erect posture of humans, perineal hernia is more common in quadrupeds than in humans.

By definition the pelvic diaphragm is the floor of the pelvic basin and the roof of the perineum. The hernial sac passing through any abnormal opening of the pelvic diaphragm will eventually appear in the perineal area. It may be anterior or posterior to the superficial transverse perineus muscle.

A primary perineal hernia may occur anterior or posterior to the superficial transverse perineus muscle (Fig. 28-42).

An anterior perineal hernia passes through the pelvic and urogenital diaphragms, lateral to the urinary bladder and vagina, and anterior to the urethra. It has been variously called pudendal, labial, lateral, or vaginal-labial. It is found only in women; it is hard to see how this kind of perineal hernia could occur in males.

A posterior perineal hernia passes between components of the pelvic diaphragm or through the hiatus of Schwalbe, when present, lateral to the urethra, vagina, and rectum. The hiatus is formed by the nonunion of the obturator internus and levator ani muscles. There are two possible locations: (1) an upper posterior hernia between the pubococcygeus and iliococcygeus muscles; and (2) a lower posterior hernia between iliococcygeus and coccygeus muscles, below the lower margin of the gluteus maximus muscle.

In males the perineal hernia enters the ischioanal fossa. In females it may enter the fossa or the labium majus, or it may lie close to the vaginal wall or below the lower margin of the gluteus maximus muscle.

A perineal hernia may be approached for repair through the perineum or through the abdomen.

Surgical Considerations


If the membranous urethra is injured proximal to (above) the urogenital diaphragm, extravasating urine and blood will pass into the space of Retzius in an extraperitoneal position. If the membranous urethra is injured distal to (below, or inferior to) the urogenital diaphragm, extravasating urine and blood will pass into the superficial perineal cleft. Extension upward to the anterior abdominal wall between the membranous superficial fascia of Scarpa and the deep muscular fascia (Gallaudet) is also possible. Details about repairing rupture of the urethra and urinary extravasations can be found in the chapter on the urethra.

The lower posterior wall of the vagina is supported by the central perineal tendon. Damage to the tendon during delivery is the cause of vaginal prolapse.

Infection of the nonpalpable Bartholin glands may present as unilateral or bilateral painful cystic swellings. Incision and drainage, with total excision of the cyst and marsupialization of the edges, is the treatment of choice.

There are several approaches to reconstructive surgery of the pelvis and perineum. Jurado et al.47 recommend a rectus abdominis flap for primary vaginal and pelvic floor reconstruction.

For pelvic floor reconstruction after surgery for locally advanced rectal carcinoma, Small et al.48 stress the role of muscle and myocutaneous flaps as biologic spacers to help prevent radiation injury, post-radiation fistulas, small bowel obstruction, and pelvic sidewall adherence.

NOTE: The numerous surgical considerations in this area will be discussed individually with each pertinent organ in other chapters.

Anatomic Complications

The anatomic complications of the pelvic floor are the complications of surgery of the several anatomic entities that are related to the pelvic floor.



The chapter in this book on the anorectum covers much of the same subject matter as that presented here, but if we discussed the pelvis without some accompanying discussion of the perineum, it would be incomplete. Therefore a very brief discussion of the perineum follows.


The hindgut of the gastrointestinal tract, with its endodermal lining, ends blindly in the cloaca. At its ventral aspect, the cloaca characteristically has a diverticulumlike formation (the allantois), which is the urachus in the adult.

The urorectal septum, of mesodermal origin, divides the cloaca into anterior and posterior parts. The anterior (urogenital) portion contains several perineal muscles. The posterior segment (terminal hindgut) encompasses the external sphincter of the anus.

One tubular structure, the mesonephric duct (ductus in the male), enters the anterior part of the cloaca. The duct (or vas) produces another tubular structure (the ureter) that travels upward to meet the metanephros. The common channel of ductus and ureter is located close to the posterior wall of the urinary bladder and is absorbed later. Each of these tubes has different openings and, therefore, different embryologic and anatomic destinies.

The reader will find more details on the perineum in the chapters on the anal and genital areas.

Surgical Anatomy


Definition of Perineum

In the anatomic (upright or erect) position, the perineum is a narrow area of soft parts located between the musculature of the gluteal and thigh areas (Fig. 28-43). With abduction of the thighs, the perineum has a diamond-shaped configuration (Fig. 28-44). The diamond is bordered by the ischiopubic rami and pubic symphysis in its anterior half, the urogenital triangle. In its posterior half, or anal triangle, boundaries are provided by the inferior border of the gluteus maximus muscle, the ischial tuberosities, the sacrotuberous ligaments, and the coccyx.

Fig. 28-43.

Boundaries and subdivisions of perineum (diamond-shaped region) (see Fig. 28-42). Perineal membrane is pierced by urethra. Female vagina also pierces this perineal membrane. (Modified from Moore KL. Clinically Oriented Anatomy (2nd ed). Baltimore: Williams & Wilkins, 1985; with permission.)

Fig. 28-44.

Diamond-shaped perineum or perineal region extends from symphysis pubis to coccyx. Transverse line between right and left ischial tuberosities divides perineum into two triangular areas: urogenital region or triangle, anteriorly, and anal region or triangle, posteriorly. (Modified from Moore KL. Clinically Oriented Anatomy. Baltimore: Williams & Wilkins, 1980; with permission.)

To some gynecologists, “perineum” refers to the midline, fibromuscular structure between the urethra and anus. Others apply the term “perineal body” to this central fixation body into which the levator ani, external sphincter ani, bulbospongiosus, and transverse perineus muscles insert or originate in part. As per Rufus49 in this section’s introduction, the ancients used the word “perineum” to refer to the male genitalia and the word “uterus” to indicate its female counterparts. It is apparent that the term has been broadened considerably in its applications.

Orientation and Relations of the Perineum

The perineum as presently defined is located below the pelvic diaphragm, the musculofascial floor of the pelvis. The fascia of the pelvic diaphragm in the region of the urogenital hiatus is fused with the inferior fascia (perineal membrane) of the “urogenital diaphragm.”50,51 It provides a plane of connective tissue that serves as the meeting point of the pelvic floor and the superior extension of the perineum-based entities, chiefly the sphincter urethrae musculature. The terminal portions of the digestive tract and the male and female urogenital tracts pass through the midline hiatuses of the pelvic diaphragm and emerge in the perineum. For all practical purposes, the bony, muscular, and fascial elements of the pelvic diaphragm and perineum support the viscera and aid the function or limit the outlets of pelvic organs.

When learning or reviewing relations of perineal structures, remember that the term “superficial” implies a relationship closer to the skin. “Superficial” is synonymous with “inferior.” The terms “deep” and “superior” mean that a structure is farther away from the skin or genitalia of the perineum. For example, the bulbospongiosus muscles are relatively superficial in the perineum. The sphincter urethrae muscle is relatively deep.

General Topography

Boundaries of the Perineum

The perineum is a diamond-shaped region. The arcuate pubic ligament, the tip of the coccyx, and the ischial tuberosities form its angles (Fig. 28-43, Fig. 28-44).

Following are the boundaries of the perineum:


Anterior: pubic symphysis

Anterolateral: ischiopubic rami

Inferolateral: ischial tuberosities

Posterolateral: sacrotuberous ligaments and gluteus maximus

Posterior: coccyx

Subdivisions of the Perineum

An imaginary line between the two ischial tuberosities divides the perineal diamond into two triangles: a ventral or anterior urogenital triangle and a dorsal or posterior anal triangle (Fig. 28-44).

In some books the posterior triangle is called the anorectal triangle. This is not correct terminology because the rectum ends at the puborectal sling. The puborectal sling is where the puborectalis muscle causes the critical angulation affecting fecal continence between the anteriorly directed rectum and the posteroinferiorly aligned anal canal.

Perineum Complex

(Fig. 28-45) The list that follows is of anatomic entities and spaces related to the perineum and pelvic floor. Some of these entities and spaces have been discussed previously in this chapter or elsewhere in this book. We mention them in the context of the perineum and pelvic floor to better explain a complex area of the human body.


Membranous fascial layer of Colles and superficial perineal cleft below (see “Superficial Fascia” under “Inguinofemoral Area” in chapter on abdominal wall and hernias)

Superficial perineal pouch (superficial compartment)

Deep perineal pouch (urogenital diaphragm)

Ischioanal (formerly ischiorectal) fossae (see “Ischioanal Fossa” under “Rectum and Anal Canal” in chapter on large intestine and anorectum)

Various fasciae of the perineum

Perineal center (perineal body)

Pelvic diaphragm

Fig. 28-45.

Layers of perineum from superficial to deep. Male, left; female, right. Below the perineal membrane, the superficial perineal pouch or space contains the muscles (A) associated with the erectile bodies. In B, the erectile bodies themselves are shown. The urogenital hiatus, which is sealed inferiorly by the perineal membrane that extends between the ischiopubic rami (C), contains the external urethral sphincter and deep transverse perineal muscles (D). In E, the pelvic outlet is almost filled by the pelvic diaphragm (levator ani and coccygeus muscles), which forms the roof of the perineal compartment. The urethra (and vagina in females) passes through the urogenital hiatus anteriorly and the rectum posteriorly. (Modified from Moore KL, Dalley AF. Clinically Oriented Anatomy, 4th ed. Philadelphia: Lippincott, Williams & Wilkins, 1999; with permission.)

Figure 28-45 illustrates the perineal layers in a highly diagrammatic way to aid orientation. The deeper structures appear more realistically in Figures 28-46, 28-47, 28-48, and 28-49.

Fig. 28-46.

Perineal view of bladder and urethral sphincter showing sphincter relations to urethra and deep transverse muscle of perineum (4-year-old male). (Modified from Oelrich TM. The urethral sphincter muscle in the male. Am J Anat 1980;158:229-246; with permission.)

Fig. 28-47.

Median section of bladder, urethra, prostate, and urethral sphincter showing extent of contact between urethra and urethral sphincter muscle (21-year-old male). (Modified from Oelrich TM. The urethral sphincter muscle in the male. Am J Anat 1980;158:229-246; with permission.)

Fig. 28-48.

Oblique view of prostate and urethra with urethral sphincter muscle removed (25-year-old male). (Modified from Oelrich TM. The urethral sphincter muscle in the male. Am J Anat 1980;158:229-246; with permission.)

Fig. 28-49.

Urogenital views of 27-year-old woman. A, Perineal view of urogenital sphincter musculature with perineal membrane removed. B, Complete urogenital sphincter musculature, bladder, and vagina with pubic symphysis removed and ischial rami spread. C, Oblique view of complete urogenital sphincter muscles, bladder, and vagina. Arrows indicate continuity of vaginal wall beneath muscle. (Modified from Oelrich TM. The striated urogenital sphincter muscle in the female. Anat Rec 1983;205:223-232; with permission.)

Layers of the Urogenital Triangle

Progressing from superficial to deep (or inferior to superior), the urogenital triangle contains the following layers (Fig. 28-45):


Skin and adipose layer (Camper’s fascia, continuous with the same layer of the anterior abdominal wall) of superficial fascia

Membranous layer of superficial fascia, named Colles’ fascia in the perineum (continuous with Scarpa’s fascia of the abdominal wall)

Superficial perineal cleft, a potential space between Colles’ fascia and the muscular fascia (fascia of Gallaudet or external perineal fascia) of the superficial perineal compartment or superficial pouch

Superficial perineal pouch including muscle fascia inferiorly (Gallaudet) and the perineal membrane superiorly. Three pairs of muscles, two pairs of erectile tissue bodies, and, in the female, the vestibular glands

The deep pouch or urethrogenital compartment (urogenital diaphragm)

The superficial and deep fasciae of the urogenital region are continuous with similar fascial layers on the anterior abdominal wall. The potential space between these fascial layers is separated from similar potential spaces in the thighs by the stout attachments of the fasciae to the ischiopubic rami. These separate the perineal space from the thigh. The attachment along the inguinal crease of Scarpa’s membranous fascia of the abdominal wall to the fascia lata of the thigh separates the interfascial potential space of the abdominal wall from extension into the thighs.

Skin and Adipose Layer of Superficial Perineal Fascia (Camper’s)

The superficial adipose layer of the urogenital triangle is called Camper’s fascia, as is the similar layer in the anterior abdominal wall. This layer of tissue continues into the anal triangle of the perineum posteriorly. Camper’s fascia of the urogenital triangle provides the bulk of tissue occupying the ischioanal fossae on either side of the midline raphe and anus.

Membranous Layer of Superficial Perineal Fascia (Colles’)

The irregularly membranous, often laminated layer of tissue deep to Camper’s fascia is called Colles’ fascia. It is the counterpart of Scarpa’s fascia of the abdominal wall. The membranous tissue is stoutly attached to the ischiopubic rami laterally and to the posterior edge of the urogenital musculature posteriorly. This provides an anatomic barrier between the urogenital spaces anteriorly and the ischioanal fossae posteriorly.

One should realize that a singular, well defined layer of membranous fascia is seen infrequently in the lower part of the anterior abdominal wall. A similar deterrent to simplicity and ease of understanding is seen also in the urogenital region. Simply put, one can encounter more than one layer of structurally membranous tissue in the perineum with a variable quantity of fatty tissue separating it from a subjacent layer of membranous tissue. This also occurs in the lower abdominal wall.

Tobin and Benjamin52 took a very clear and well defended position in disputing the existence of separate adipose and membranous layers of fascia on the anterior abdominal wall or in the perineum. Current interpretations of the original work of Colles, Scarpa, and Camper are not accurate expressions of their stated observations.

Superficial Perineal Cleft

Boundaries of the Superficial Perineal Cleft

Following are the boundaries of the superficial perineal cleft:


Inferior (below): Colles’ fascia

Superior: muscle fascia of Gallaudet (inferior or external perineal fascia)

Lateral: Colles’ fascia, attached to the ischiopubic rami

Posterolateral: closed by the union of Colles’ fascia and muscle fascia

Anterior: communicates freely with the potential space between Scarpa’s fascia and the anterior abdominal wall, laterally and superiorly

Nature of the Superficial Perineal Cleft

Irrespective of the diversity in appearance of laminae of membranous tissues in the superficial fascia of the urogenital triangle, in every dissection we have performed on embalmed or unembalmed cadaveric specimens, we have been able to find a clearly demonstrable cleft, or potential space, between the superficial fascia and the fascia that covers the muscles of the superficial perineal compartment (Fig. 28-50).

Fig. 28-50.

Diagrammatic sagittal section of pelvis showing six unpaired spaces of pelvis. All are potential spaces except for rectouterine space of Douglas in female (rectovesical space in male) which is a true space lined with peritoneum. (Modified from Skandalakis LJ, Gadacz TR, Mansberger AR Jr, Mitchell WE Jr, Colborn GL, Skandalakis JE. Modern Hernia Repair. Pearl River NY: Parthenon, 1996; with permission.)

Perhaps in any given individual there is a plane of least resistance within the superficial fascia where the fat and laminae of connective tissue can be separated with relative ease. Perhaps, too, this particular plane may depend greatly upon the exact point of entry or perforation. For all practical purposes, the superficial perineal cleft may be at one and the same time both artifactual and real upon interruption of the most readily dissectible line of separation. Although maintaining the existence of both adipose and membranous layers of superficial fascia in the perineum, Stormont et al.53 acknowledged that the “membranous layer” is probably fenestrated.

The superficial perineal cleft can be probed with the fingertips without sharp dissection. After entering this space, blunt dissection upward ventrally from the region anterior to the perineal body, lateral to the scrotum, or deep to the subcutaneous tissues of the mons veneris reaches a continuing potential space of the lower abdominal wall. Likewise, defining the interval between superficial and deep fasciae of the abdominal wall allows tracing out the potential space inferiorly into the perineum. Extravasation of blood and/or urine into this space takes place in perineal injuries of the urethra external to the perineal membrane.

It is important to recognize and remember the difference between the superficial cleft and the superficial pouch or compartment. The superficial perineal cleft is a potential space between the membranous layer of superficial fascia and the fascia of Gallaudet. Perhaps, for easy understanding, it can be thought of as existing between Colles’ fascia and the deep perineal fascia that covers the superficial perineal muscles.

The adipose and membranous layers of superficial fascia blend as they approach the external genitalia. The fatty element is essentially lost. The superficial tissue is richly infiltrated with smooth muscle fibers, forming the dartos tunic of the scrotum and the superficial fascial covering of the penis/clitoris. Near the midline of the anterior abdominal wall, this superficial fascial blending is considerably thicker and forms the fundiform ligament of the penis or clitoris.

Superficial Perineal Pouch

The superficial perineal pouch (Fig. 28-51) includes the space between the fascia of Gallaudet and the perineal membrane. It is composed of the following structures (from external to internal), which are discussed below:


External perineal fascia or muscle fascia of Gallaudet

Paired muscles of the superficial compartment (Fig. 28-45A)


– Ischiocavernosus

– Bulbospongiosus

– Superficial transverse perineus

Paired erectile tissue elements


– Corpora cavernosa penis or clitoris

– Corpora spongiosa (penile bulb or vestibular bulbs)

Right and left vestibular (Bartholin) glands in the female (Fig. 28-45B)

Perineal membrane



Fig. 28-51.

Schematic of midline sections showing urogenital diaphragm and perineal spaces (pouches). Shows superficial perineal fascia (Colles’ fascia) as continuation of deep or membranous layer (Scarpa’s fascia) of superficial fascia of abdomen. CPT, Central perineal tendon (perineal body). APL, Arcuate pubic ligament. (Modified from Moore KL. Clinically Oriented Anatomy (2nd ed). Baltimore: Williams & Wilkins, 1985; with permission.)

External Perineal Fascia of Gallaudet

The most superficial element in the superficial pouch is the external muscle fascia of Gallaudet. It covers the muscles and, between the erectile tissues, joins the deeper-lying perineal membrane. The fascia of Gallaudet covers the external abdominal oblique muscle (the so-called innominate fascia) and the deep fascia (Buck’s fascia) of the penis or clitoris. However, some anatomists believe that the fascia of Buck is not related to the fascia of Gallaudet.


The membranous fascia of Scarpa of the anterior abdominal wall is renamed Colles’ in the perineum. Colles’ is superficial fascia. Gallaudet is deep fascia. The fascia of Colles and the fascia of Gallaudet bound the superficial perineal cleft (or space); the (deep) fascia of Gallaudet and the perineal membrane bound the superficial pouch, or superficial perineal compartment. To emphasize: Colles’ fascia is superficial fascia in the perineum; Gallaudet is deep, muscular fascia in the perineum.

The suspensory ligament of the penis or clitoris originates from the deep fascia just above and ventral to the symphysis pubis. The suspensory ligament is on the same deep plane as Buck’s fascia and the fascia of Gallaudet. The dorsal arteries, nerves, and superficial veins lie deep to Buck’s (deep) fascia on the penis or clitoris. The deep dorsal vein is invested by the fascia.

Muscles of the Superficial Compartment

The following paragraphs discuss the paired muscles of the superficial compartment (Fig. 28-52).

Fig. 28-52.

Ejaculatory musculature. (Modified from Hinman F Jr. Atlas of Urosurgical Anatomy. Philadelphia: WB Saunders, 1993; with permission.)


The paired ischiocavernosus muscles have an extensive bony origin that begins posteriorly at the anterior part of the ischial tuberosities and continues forward on the ischiopubic ramus. Some fibers arise from the underlying perineal membrane. The ischiocavernosus muscles embrace the crus of each of the corpora cavernosa penis or clitoris at their attachments proximally to the ischiopubic rami. The ischiocavernosus muscles insert upon the tunica albuginea of the proximal parts of the shafts of the corpora, the crus penis or crus clitoris.

The more medially situated muscle fibers of the ischiocavernosus are often difficult to separate from bundles of the bulbospongiosus muscles without artifactual division. Contraction of the ischiocavernosus results in some restriction of venous flow from the corpora cavernosa penis and clitoris that contributes to erection of these elements.


The bulbospongiosus muscles (Fig. 28-52) arise from the perineal body and membrane. They are invested externally by the muscle fascia of Gallaudet. They join in the midline of the male penile bulb by fusing along the midline raphe. In the female, they are separated by the pudendal cleft and cover the vestibular bulbs. The insertions of the bulbospongiosus are upon the proximal part of the corpus spongiosum in the male and the ventral extensions of the vestibular bulbs in the female.

In the male, the bulbospongiosus assists in urethral compression, “stripping” it in micturition and ejaculation. Its contraction assists also in restricting venous flow from the corpus spongiosum, contributing to the process of erection. In the female, the bulbospongiosus muscles provide an external sphincter for the vaginal introitus.

Superficial Transverse Perineus Muscles

The superficial transverse perineus muscles (Fig. 28-45A, Fig. 28-52) arise bilaterally from the ischial tuberosities and insert anteromedially into the centrally located perineal body. They thereby interconnect the perineal body and the ischium in a nearly transverse way.

The superficial transverse perineus is occasionally absent. More often, it is simply difficult to define in older individuals, wherein it may be replaced by fibrous tissue. It is more difficult to find in the older female than in the older male. Some of the difficulty in finding this muscle may be due partly to atrophy with the passage of many years. Another contributing cause is that the perineal branches of the pudendal nerve and internal pudendal vessels frequently pass through the muscle, separating it into poorly defined fasciculi of muscle bundles. Tracing the neurovascular elements often destroys these bundles.

The muscle acts to fix the central fibromuscular point of the perineum, presumably assisting in the maintenance of urinary and fecal continence. Its central insertion is perpendicular to that of the external anal sphincter, and can be seen during perineal excision of the anal canal. Its motor supply, like that of other muscles of the superficial pouch, is derived from the perineal branch of the pudendal nerve from S2, S3, and S4.

Erectile Tissues and Glandular Elements

Because the penis is suspended from the anterior abdominal wall in lower animals, the surface of the human penis which faces forward when in the flaccid state is not truly the ventral surface; it is the dorsal surface, for it becomes dorsal in position when erect.

The corpora of the penis is composed of three bodies of cavernous, erectile tissue.


Paired corpora cavernosa penis on either side

Corpus spongiosum medially

Corpora Cavernosa of the Penis and Clitoris

The crura (proximal or posterior parts of the corpora cavernosa) of the clitoris and penis arise from the ischial tuberosities and the rami of the ischia. Near the symphysis, the two crura are attached to the pubic bone by deep fascial connections and then bend ventrally, becoming the corpora cavernosa. Thereafter, joined by a midline fibrous septum and surrounded by a common fibrous investment, they form the body of the clitoris in the female. In the male, a ventral groove between the two corpora is occupied by the corpus spongiosum and the contained urethra.

Each corpus cavernosum of the penis or clitoris is surrounded by a tough fibrous tunica albuginea intermingled with a network of elastic fibers. The superficial layer of this tunic is composed of longitudinally oriented fibers, providing a singular tubelike covering for the two corpora. Each corpus has a separate investment of deep, circularly arranged fibers that join at the median septum. This septum completely separates the two crura proximally. Because the septum is perforated distally, the cavernous tissues of the crura communicate very freely here.

Within the corpora, a trabecular meshwork of smooth muscle bundles and a collagenous extracellular matrix receive arterial supply by the helicine branches of the right and left cavernous branches of the internal pudendal arteries (Fig. 28-53). The helicine arteries enter a complex vascular network of sinuses or lacunae lined with endothelial cells. Venules beneath the tunica albuginea provide the venous drainage for the corpora. The venules coalesce to form emissary veins. These pierce the tunic and drain to the deep dorsal vein of the penis or clitoris.54

Fig. 28-53.

Vasculature and innervation of penile shaft (cross-section). (Modified from Hinman F Jr. Atlas of Urosurgical Anatomy. Philadelphia: WB Saunders, 1993; with permission.)

In the flaccid state, the smooth muscle is tonically contracted under sympathetic stimulation and very little arterial flow enters the corpora (4 ml/min/100 g of tissue). Appropriate stimuli and parasympathetic outflow result in vasodilation of the arteries and relaxation of the smooth muscle, with concomitant compression of the peripheral venules against the tunica albuginea. This action provides the basis for erection. Sympathetic stimulation and the release of norepinephrine and other agents cause contraction of the smooth muscle, release of the venous compression, and the return to detumescence and flaccidity. The role played by the so-called polsters or cushions in the vessels of the corpora (described by McConnell et al.55 and Conti et al.56) remains unresolved.

Corpus Spongiosum

The midline corpus spongiosum of the male (corpus cavernosum urethrae) ends as the expanded glans penis and transmits the penile urethra. The acorn-shaped glans penis forms a cap for the two corpora cavernosa. Its free margin is called the corona of the glans.

The corpus spongiosum, like the corpora cavernosa, is surrounded by a dense fibroelastic, unexpandable covering, the tunica albuginea. This relative inelasticity allows it to become firm when its vascular spaces are perfused with arterial blood at a rate that exceeds the rate of venous drainage. The tunica albuginea of the corpus spongiosum is thinner than that of the corpora cavernosa. The tunica and glans penis are therefore less rigid during erection than the corpora cavernosa. This allows the ejaculate to pass.

MacBride and Blight57 estimate the tunica albuginea of the corpus cavernosum penis to be about 1.4 mm thick in unembalmed and embalmed cadavers, decreasing in thickness with advancing age unless fibrosis is present. The tunica of the corpus spongiosum, in contrast, is typically only about 0.3 mm thick and exhibits relatively little variation in thickness attributable to aging.

The male corpus spongiosum begins as the expanded penile bulb, formed by the fusion of two anlagen within the superficial perineal pouch. The urethra passes into the penile bulb after traversing the urethral sphincter and perineal membrane (urogenital diaphragm). After a distance of about 2.5 cm, the urethra receives the ducts of the two bulbourethral glands (of Cowper) which reside within the urogenital sphincter muscle. Here, the urethra is also characterized by the presence of the mucosal urethral glands (of Littre). At the distal end of the pendulous portion of the penis, the urethral lumen expands within the glans penis as the fossa navicularis.

The penile urethra is represented by the vestibule of the vagina, retaining the embryologic condition of the urethral groove. The unfused urethral folds on either side of the urethral groove develop into the labia minora. The original embryologic genital swellings of the female are represented by the labia majora. In the male, they form the definitive scrotum. The external meatus of the female urethra opens just above the superior aspect of the vaginal introitus (opening). On either side of the urethral meatus are the openings for the paraurethral (Skene’s) glands, the female counterpart of the prostate.

Vestibular (Bartholin) Glands

In the female, the two anlagen that fuse to form the penile bulb are represented by the two vestibular bulbs. These bulbs fuse anteriorly to form the threadlike commissure of the clitoris and expand distally as the glans clitoris. The greater vestibular glands lie within the superficial pouch, deep to the proximal ends of the vestibular bulbs and on either side of the vaginal introitus (Fig. 28-45B). The greater vestibular glands are better known as Bartholin’s glands. They are small, somewhat ovoid glands whose secretory products include both lubricating and endocrine elements. According to Fettisoff et al.58 (as cited in Gray’s Anatomy59), the endocrine elements secreted by the glands include serotonin, calcitonin, bombesin, hCG, and katacalcin. The ducts of these mucous secreting glands open at about the 5 o’clock and 7 o’clock positions relative to the vaginal introitus, between the hymen and the labia minora.

The penile bulb and vestibular bulbs are covered by the bulbospongiosus muscle. In the female, the medial fascicles of the bilateral muscles attach to the deep fascia of the dorsum of the clitoris. The lateral fascicles attach to the perineal membrane.

Perineal Membrane

The perineal membrane (Fig. 28-51) provides a “roof” for the superficial pouch and a “floor” for the deep pouch (urogenital diaphragm). For all practical purposes, the perineal membrane is the inferior fascia of the urogenital diaphragm. We agree with Last,8 however, that in most cases the portion of the perineal membrane that is related to the under surface of the pelvic diaphragm (levator ani muscles) is actually areolar tissue, and that “no definitely formed membrane exists” there. Therefore a rigid description of the geographic territory of the deep perineal pouch and its contents is difficult. For a better understanding of this complicated area of the human body and for better knowledge of the contents of the deep perineal pouch we consider the perineal membrane to be present on the under surface of the levator ani muscles, thus forming a complete envelope together with its inferior layer.


The vasculature of the superficial perineal pouch consists of the following:


Posterior scrotal/labial branches of the perineal branch of the internal pudendal vessels

Transverse perineal branch of the perineal branch of the internal pudendal artery (supplying the superficial transverse perineus muscle and tissue between the bulb and the anus)

Also, the following arteries which enter the superficial pouch by piercing the perineal membrane, after arising from the internal pudendal artery in the deep pouch:


– Artery of the bulb

– Artery of the urethra

– Deep artery of the penis or clitoris


The following are the nerves of the superficial perineal pouch:


Perineal branches of the pudendal nerves:


– Cutaneous branches (posterior scrotal/labial nerves)

– Muscular branches (transverse perineal nerves)

Perineal branches of the posterior femoral cutaneous nerve of the thigh

Urogenital Diaphragm (Deep Pouch or Compartment)

The urogenital diaphragm is a fibromuscular layer between the pelvic floor (levator ani muscles) limited inferiorly by the perineal membrane.

Support Function of the Deep Pouch

The ventral position of the structures within the urogenital diaphragm (Fig. 28-35) participates also in the separation of the perineum from the pelvis. This position provides an anterior support for the viscera located above the defect of the pelvic diaphragm (urogenital hiatus) between the right and left pubococcygeus muscles of the pelvic floor (Fig. 28-54). Thus, the pelvic viscera are protected and supported both by internal structures (endopelvic fascia, visceral ligaments, and levator ani and its fasciae) and external structures (urogenital diaphragm and elements of the superficial perineal compartment).

Fig. 28-54.

Pelvic supporting structures. The urogenital diaphragm, together with endopelvic fascia and the levator ani, provides anterior support for urogenital organs. (Modified from Toldt C, Hochstetter F. Anatomischer Atlas. Munich: Urban & Schwarzenberg, 1976; with permission.)

Urogenital Diaphragm Reexamined

The term “urogenital diaphragm” is sometimes used as a synonym for the perineal membrane or triangular ligament. Most anatomic and clinical sources state that the urogenital diaphragm is composed of two connective tissue layers, the superior and inferior fasciae.

The superior layer of fascia and inferior layer of fascia (the perineal membrane, Fig. 28-45C) enclose the deep perineal compartment or pouch containing two muscles and, in the male, bulbourethral (Cowper’s) glands (Fig. 28-45D). The “sandwich” formed by these two layers of fascia and the contents of the deep space (pouch) comprises the urogenital diaphragm (Fig. 28-45C, D).

Superficial (membranous layer) and deep perineal fascia attach to the ischiopubic ramus and to the posterior margin of the urogenital diaphragm and enclose the superficial perineal compartment (pouch). This area is a complex mixture of striated and smooth muscle structures arranged between the two roughly horizontal fascial laminae.

The superior and inferior fascial layers ostensibly join each other posteriorly. They provide a transversely oriented “touchdown” line for merging with the muscle fascia of Gallaudet of the superficial pouch and with the fascia of Colles. This effectively closes the superficial perineal pouch and superficial perineal cleft simultaneously.

Anteriorly, the perineal membrane and the superior layer of the diaphragm fuse into a flat, tough band of tissue, the transverse perineal ligament. The superior fascial layer, according to most contemporary sources, separates the prostate gland from the sphincter urethrae muscle and fuses medially with the inferior fascial layer of the pelvic diaphragm.

Convincing studies by Oelrich41,50,51 cast doubt upon the existence of a superior layer of fascia of the urogenital diaphragm, at least as typically described. According to Oelrich, in the male the sphincter urethrae muscle continues superiorly through and around the substance of the prostate gland to the urinary bladder. Likewise, the same basic muscle in females continues upward from a common urethrovaginal sphincter to the sphincter urethrae and then to the bladder (Fig. 28-49C).

Because the pubococcygeus muscle of the levator ani inserts in part into the lateral walls of the vagina and also into the perineal body, the urogenital hiatus of the female seals laterally. Therefore, the hiatus principally transmits endopelvic fascia, the urethra, and its sphincter. These structures also attach ventrally to the lower part of the pubic bone by the pubovesical and pubourethral ligaments, thereby assisting in closure of the urogenital hiatus.

According to Oelrich, the superior fascia of the pelvic diaphragm is the fascial layer passing through the hiatus and blending with the perineal membrane.50 The term “urethrovaginal compartment,” as he suggests, might be a more accurate name than urogenital diaphragm in the female.51 Unfortunately, he did not offer an alternative name for the male. Perhaps “urethrogenital compartment” might be more accurate for both genders. Without adding further to the confusion of nomenclature, we will hereafter use this name or “deep compartment” or “deep pouch” to designate this rather irregularly shaped complex of muscle and connective tissue.

The findings of Strasser et al.60 appear to agree essentially with Oelrich.50 They observe that the sphincter urethrae muscle of the male extends inferiorly from the bladder to the penile bulb without interruption. As the sphincter urethrae continues inferiorly from the bladder it surrounds the prostate gland, contributing to the prostatic sheath. The prostate develops within the sphincter urethrae embryologycally, and its enlargement thereafter thins the surrounding portion of the sphincter urethrae.

Strasser et al.60 further noted that the fibers of the most inferior part of the sphincter urethrae muscles are arranged omegalike about the anterior and lateral aspects of the urethra, inserting posteriorly into the perineal body. Like Oelrich,50 they asserted that the “urogenital diaphragm,” as usually described, does not exist.

Urethral Sphincter Complex

Delancey61 agreed with Oelrich50,51 that the most proximal part of the striated urethral sphincter is circularly oriented and surrounds the smooth muscle of the wall of the urethra. Distally, these striated fibers lie within the deep pouch. Some encircle the urethra and vagina together, forming a combined urethral and vaginal sphincter. Others exit laterally and attach at the pubic rami and also, presumably, to the perineal membrane, as the compressor urethrae. Near the vesical neck, fibrous tissue and smooth muscle fibers from the vagina and urethra run anteriorly to attach to the pelvic wall, forming the pubourethral ligament.

A second group of connective tissue and smooth muscle fibers (known as the fibers of Luschka) connect the paraurethral sulci of the vaginal wall to the pubococcygeus muscle. Delancey called this the vaginolevator attachment.61 Above this, the vaginal wall is attached to the levator by means of the arcus tendineus fascia pelvis.


Superior Fascia of the Urogenital Diaphragm

In the male, the periprostatic sheath covers the prostatic capsule and its venous plexus (Fig. 28-55). Krongrad and Droller62 report that the periprostatic sheath is composed of a coalescence of pelvic fascia and aponeurotic tissue. This tissue anchors the prostate to the sheath of the bladder above, the urogenital diaphragm inferiorly, the levator ani laterally, and the rectovesical fascia posteriorly. Further, it attaches to the pubis anteriorly by the puboprostatic ligaments.

Fig. 28-55.

Transverse section of the prostate gland and urethra, at the level of the seminal colliculus. Note the connective tissue capsule of the gland. (Modified from Toldt C, Hochstetter F. Anatomischer Atlas. Munich: Urban & Schwarzenberg, 1976; with permission.)

Analyzing the pertinent literature and comparing it with our own observations, we agree with Oelrich50,51 that the fascial complex in the male forms the superior and circumferential border of the deep pouch, a rather conical musculofascial compartment. The connective tissue attaches to the perineal membrane inferiorly. This construct is very dissimilar to the concept of a simple, flat, horizontal, roughly triangular “urogenital diaphragm.” According to Krongrad and Droller,62 the anterior periprostatic fascia (puboprostatic fascia of Denonvilliers, fascia of Zuckerkandl or Delbet) extends to the lower border of the pubic bone, where it covers the venous plexus of Santorini.

The superior fascia of the deep pouch, or urethrogenital compartment, is difficult to demonstrate. There is great complexity in its interrelationships and coalescence with the superior and inferior fasciae of the pelvic diaphragm, pubovesical and vaginal fascia, and the prostatic fascial capsule. In the male, the superior fascia of the deep pouch clearly does not form a complete barrier between the musculature of the deep pouch and the muscle fibers of the prostate gland and prostatic urethra, as commonly supposed.

The superior layer of fascia of the pelvic diaphragm and the perineal membrane fuse together anteriorly without the intervention of muscle fibers. They form a tough fibrous band called the transverse perineal ligament. This effectively closes the deep pouch a short distance beneath the pubic arch and pubic arcuate ligament.

The dorsal nerves and arteries of the penis (clitoris) pierce the transverse perineal ligament as they leave the deep pouch to reach the dorsum of the penis (clitoris). The deep dorsal penile or clitoral vein passes between the transverse perineal ligament and the pubic arcuate ligament to enter the pelvic venous plexus. This space transmits a single or bilateral accessory pudendal artery in about 10%11 of individuals, a vessel which may provide the dorsal artery and/or deep artery of the penis (clitoris).

Inferior Fascia of the Deep Pouch

The inferior fascia of the deep pouch is more highly organized and distinct than the superior layer. It is located between the two sides of the pubic arch and is known as the perineal membrane. Some refer to this tough layer of connective tissue as the urogenital diaphragm. It is also called the “triangular ligament,” although its configuration is more trapezoidal than triangular. In light of the foregoing discussion, we might accept the term “urogenital diaphragm” as an alternative name for the perineal membrane.

The deep fascia on the inferior or superficial surface of the urogenital diaphragm is thickened to form the dense perineal membrane. It is continuous with the deep layer of fascia anteriorly and posteriorly. The perineal membrane is pierced by the urethra; in the female, the vagina also pierces this membrane.

The perineal membrane provides a “roof” for the superficial perineal pouch and a substructural basis for attachment of erectile tissue elements and muscles of that pouch. In addition, the perineal membrane acts as the “floor” for the deep pouch and its musculature.

Muscles of the Deep Compartment

The muscles contributing to the urogenital diaphragm, as described in former years, included only two rather simply described muscles. These were the paired deep transversus perineus muscles and the sphincter urethrae. The terminology and form of these muscles were assiduously memorized by generations of obstetricians/ gynecologists, surgeons, and anatomists and many, many medical students. All pretended to see, or imagined that they saw, the structures depicted in the simple two-dimensional diagrams copied from one book to the next.

Studies including those by Krantz,63 Oelrich,50,51 and Tichy42 introduced additional terminology and important concepts regarding structure and function in describing the musculature of the “urogenital diaphragm.”

The muscles of the diaphragm or deep pouch are listed here and discussed below. The descriptions of muscles of the deep pouch in the female (Fig. 28-49) are drawn from the work of Oelrich.51


Deep transversus perineus

Sphincter urethrae

Compressor urethrae (female)

Sphincter urethrovaginalis (female)

Transversus vaginalis (female)

Deep Transversus Perineus Muscle

Behind or dorsal to the distal part of the sphincter urethrae is the deep transversus perineus muscle of the perineum. This muscle’s fibers arise from the fascia of the pudendal canal. The fibers intermingle with those of the sphincter urethrae, external anal sphincter, and smooth muscle of the rectourethral muscle at the site of the perineal body in the midline.50

Sphincter Urethrae

Inferior to the prostate in the urogenital hiatus, the fibers of the sphincter urethrae are more or less circumferential (omegalike). Below the pelvic diaphragm, the sphincter expands to fill the interval between the pudendal canals. Laterally and ventrally the sphincter is associated with the rich, prostatic venous plexus and bears a resemblance to cavernous tissue. Thus, the distinctive form of the muscle is lost.

Compressor Urethrae

The compressor urethrae muscle arises laterally as a slender tendon near the anterior border of the ischial tuberosity. It expands as a band about 6 mm wide as it reaches the urethra and becomes continuous with the muscle of the opposite side. Its most ventral and superior edge lies within the urogenital hiatus, where it is continuous with the lower fibers of the urethral sphincter behind the pubic symphysis. Some of its deeper fibers attach to the lateral aspect of the urethra.

Sphincter Urethrovaginalis

The sphincter urethrovaginalis is a thin, flat muscle about 5 mm wide that surrounds both the vagina and the urethra. Its fibers are continuous across the midline behind the vagina and continuous with the compressor urethrae ventrally. None of its fibers pass between the urethra and vagina.

Transversus Vaginalis

Some striated fibers pass medially as a fan-shaped muscle from the vicinity of the compressor urethrae to insert into the anterior half of the lateral wall of the vagina, superior to the level of the urethrovaginalis. The more posterior of these fibers could perhaps represent the deep transversus perineus muscle, although Oelrich51 denies the presence of this muscle in the female.

Membranous Urethra

By “membranous urethra” we mean that part of the urethra just superior to the perineal membrane or passing through it. Why have we called this 1 cm long, thin walled part of the urethra “membranous?” It is surrounded by muscle. This name is even more questionable in light of our foregoing observations about the superior fascial layer. For the part that traverses the corpus spongiosum, we use the term “spongy.” The part that traverses the prostate gland, we term “prostatic.” However, for the part within the deep compartment or urethrogenital diaphragm, we use the term “membranous.” Logically, it should be called the “muscular” part as proposed by Waldeyer and reported by Mermigas.64 We do not want to muddy the water further and, therefore, will continue to refer to this area as “membranous.” (See the section on the male urethra in the chapter on the male genital system; and see the section on the female urethra in the chapter on the female genital system.)

The fibers of the sphincter urethrae form a sphincter for the membranous portion of the urethra in the urogenital hiatus, inferior to the prostate. The sphincter urethrae muscle provides no covering where the urethra penetrates the perineal membrane and angulates ventrally. This portion of the urethra is termed the “bare area”65 or “pars nuda.”

The bare area is incompletely supported by the corpus spongiosum.66 Therefore, one should be cautious when using rigid urethral instruments in this area as the urethra is easily injured here.

Internal Pudendal Vessels

The internal pudendal artery arises from the anterior division of the internal iliac artery (Fig. 28-8), either within the pelvis or after the anterior division passes through the greater sciatic foramen. Thereafter the internal iliac artery also provides origin for the inferior gluteal artery.

The course of the internal pudendal artery and its vein(s) (Fig. 28-10) after entering the pudendal canal is essentially identical to that of the pudendal nerve. The differences between the nerve and vessels occur chiefly within the urethrogenital compartment. Here, the internal pudendal artery sends bulbar, urethral, and deep crural branches before ending as the dorsal artery of the clitoris/penis.

The perineal membrane, visceral fascia, and the fascia of the levator ani collectively form the envelope of the “urogenital diaphragm,” or urethrogenital compartment of the pelvic floor.

Pudendal Nerve

The pudendal nerve is formed from contributions from the ventral primary rami of S2, S3, and S4 (Fig. 28-22). The nerve or its contributors leave the greater sciatic foramen in a position medial to the internal pudendal artery and vein. They then cross the sacrospinous ligament near the tip of the spine of the ischium, and pass through the lesser sciatic foramen. The pudendal nerve may receive a contribution from S4 as it passes through the coccygeus muscle (the perineal branch of the nerve to the levator ani). Passing between the underlying sacrospinous ligament and the overlying sacrotuberous ligament and gluteus maximus muscle, the nerve enters the pudendal canal of Alcock (Fig. 28-3) in the lateral wall of the ischioanal fossa.

The walls of the pudendal canal begin as extensions of ligamentous and other connective tissue from the anterolateral edge of the sacrotuberous ligament as it passes to attach on the ischial tuberosity (Fig. 28-56). The fibers from the sacrotuberous ligament that attach to the inner surface of the ischial ramus and contribute to the canal are called the falciform ligament. Thereafter, the fascial investment from the muscle fascia of the obturator internus muscle covers the nerve and accompanying internal pudendal vessels.

Fig. 28-56.

Site of pudendal canal. (Modified from Hinman F Jr. Atlas of Urosurgical Anatomy. Philadelphia: WB Saunders, 1993; with permission.)

The pudendal nerve has three major branches: the inferior rectal nerve, the perineal nerve, and the dorsal nerve of the penis or clitoris. These branches are discussed below. Note: The branches may have already separated prior to entrance into the pudendal canal.

The first branch of the pudendal nerve, the inferior rectal nerve(s), originates as the pudendal nerve enters the pudendal canal. The inferior rectal nerve passes anteromedially through the fat of the ischioanal fossa. Here it reaches and supplies the levator ani (in part), the lining of the distal part of the anal canal, the external anal sphincter musculature, and the overlying subcutaneous tissue and skin.

Branches of the inferior rectal nerve are interconnected with the perineal branch of the posterior femoral cutaneous and posterior scrotal/labial nerves. The perineal branch of the ventral primary ramus of S4 may pierce the coccygeus and supply the skin between the anus and the coccyx. Somewhat further forward, the pudendal nerve divides into a perineal branch and the dorsal nerve of the penis or clitoris.

NOTE: In some individuals, the perineal branch of the posterior femoral cutaneous nerve figures prominently in the sensory supply of the perineum and requires selective treatment to gain adequate anesthesia of the perineum.

The perineal branch of the pudendal nerve pierces the obturator fascial wall of the pudendal canal somewhat posterior to the urogenital triangle. It frequently passes through the perineal membrane, and then the substance of the superficial transverse perineus muscle (or the cutaneous and transverse branches may pass through it separately).

The medial and lateral cutaneous branches of the perineal nerve are named either posterior labial or posterior scrotal. These branches pass through the superficial perineal cleft and Colles’ membranous fascia to reach the skin.

The transverse motor branch of the perineal nerve divides into several rami to supply the musculature of the superficial and deep pouches and assist in supplying the external anal sphincter and levator ani. The branch of the perineal nerve supplying the bulbospongiosus also provides a branch to the bulb of the urethra, supplying the corpus spongiosum and urethral mucosa.59

The dorsal nerve of the penis or clitoris, the terminal portion of the pudendal nerve, continues forward in the pudendal canal. Its course follows the lateral aspect of the urethrogenital compartment (urogenital diaphragm) in a channel characterized by trabeculated connective tissues and muscle fibers and intermingled with highly vascular tissue.

The dorsal nerve emerges from the anterior edge of the urethrogenital compartment by piercing the transverse perineal ligament. This is the tough band of tissue formed by the coalescence of the perineal membrane inferiorly and the fascia associated with the sphincter urethrae muscle superiorly. Initially, the nerve lies deep to the suspensory ligamentous tissue of the clitoris or penis and then extends to the deep fascia of the penis or clitoris. Twigs penetrate the deep fascia to supply the superficial fascia and skin (Fig. 28-57).

Fig. 28-57.

Nerve distribution to the penis and its component parts. (Modified from Toldt C, Hochstetter F. Anatomischer Atlas. Munich: Urban & Schwarzenberg, 1976; with permission.)

Contents of Deep Compartment Summarized


Two bulbourethral glands (of Cowper). These pea-sized glands are located on each side of the urethra within the male urogenital diaphragm. They drain into the spongy urethra.

Blood vessels, ducts, and nerves (bilateral):


– Internal pudendal artery and vein

– Artery of the urethral bulb

– Nerves of urethral bulb and urethra

– Deep artery of the crus

– Dorsal artery of the penis or clitoris

– Deep dorsal vein of penis or clitoris (singular, midline)

– Plexus of veins

– Duct of bulbourethral gland

– Dorsal nerve of penis or clitoris

In the female, the inferior vertical portion of the vagina is considered to be contained within the urogenital diaphragm (urethrogenital compartment).

NOTE: The main artery of the deep pouch is the continuation of the internal pudendal artery. Within the diaphragm, the internal pudendal artery gives origin to the artery of the bulb and the artery of the urethra. It then terminates by dividing into the deep artery and dorsal artery of the penis or clitoris. The deep (motor or transverse) branch of the perineal nerve is the source of the nerve supply of the musculature within the urethrogenital pouch.

Anal Triangle

The structure and function of the anal canal and the external anal sphincteric musculature are described in the chapter on the anorectum.


The base of the anal triangle is bounded anteriorly by the transverse line through the two ischial tuberosities. In a more practical sense, the superficial transverse perineus muscle, the posterior edge of the deep compartment, and the anterior extremity of the perineal body delineate the anal triangle from the urogenital triangle. Posterolaterally, the sacrotuberous ligaments and the inferior borders of the gluteus maximus muscle provide the sides of the triangle. The coccyx creates the apex of the triangle.

Ischioanal (Ischiorectal) Fossae

The midline raphe and anus divide the anal triangle into two smaller triangles that form the bases of the two ischioanal fossae (formerly, ischiorectal fossae). Each ischioanal fossa is pyramid-shaped. The apex points superiorly between the levator ani and obturator internus muscles (Fig. 28-3). The base of the pyramid faces inferiorly and is formed by fibrofatty tissue and overlying skin. Each fossa is filled with fat. The inferior rectal nerves and vessels pass through this fat toward the midline structures, including the superficial and deep parts of the external anal sphincter.

When tensed, the overlying gluteus maximus muscles push against the fatty tissue, compressing the fat of the ischioanal fossae and performing a role in maintaining fecal continence. When the muscles are relaxed, the softness of the adipose tissue allows dilation of the anal canal during defecation.

The two ischioanal fossae continue behind the anus, between the levator ani (levator plate and puborectalis) and the anococcygeal ligament (Fig. 28-37B). The anococcygeal ligament is an indistinct band of fibrofatty tissue. It contains mingled extensions of the superficial portion of the external sphincter ani as it passes from the circumanal region to the lower parts of the coccyx.

Each ischioanal fossa has an anterior extension beneath the posterior part of the deep compartment of the urogenital triangle, called the anterior recess, into which infections can spread. Similar posterior recesses extend posterolaterally beneath the sacrotuberous ligaments and the anococcygeal ligament. Abscesses in the ischioanal fossa can become quite large and extend from one fossa to the contralateral side, forming the so-called “horseshoe” abscess beneath the anococcygeus muscle and ligament.

Blood Supply of the Anal Triangle

The inferior rectal artery is a branch of the internal pudendal artery (Fig. 28-16). The inferior rectal veins are tributaries to the internal pudendal vein.

Innervation of the Anal Triangle

The anal triangle (see Fig. 28-28A&B) receives its neural and vascular supply by way of the inferior rectal nerves and vessels. The inferior rectal nerve arises from the pudendal nerve in the pudendal canal. After piercing the fascia of the obturator internus, the nerve passes anteromedially through the fatty tissue of the ischioanal fossa. Its path reaches the external anal sphincter and levator ani muscles and the mucosa of the lower part of the anal canal below the mucocutaneous junction. Cutaneous branches pass more superficially to reach the anal skin. Loss of the external sphincter following pudendal nerve injury will cause some degree of fecal incontinence.

Surgical Considerations


Grant and Basmajian67 stated that the only nerve serving the perineal area is the pudendal nerve and the only artery is the internal pudendal artery. The urinary bladder and anorectum have a common nerve supply, the hypogastric plexus and pelvic splanchnic nerves. Some writers speculate that the latter fact is the reason that, after transurethral prostatectomy, many men have bladder spasms that they perceive as an urge to move their bowels.

Pudendal nerve compression is a clinical entity that may result in chronic pain, physical disability, and severe emotional distress to the affected patient. Compression of the nerve, presumably in its perineal course, can result in pain variously localized in the perineal region; pain that can be exacerbated by standing, sexual activity, and defecation, in particular. Various invasive surgical procedures have been attempted to relieve suspected compression of, or tension upon, the nerve. These include division of the sacrospinous ligament (and, in some cases, the sacrotuberous ligament also) and dissecting the nerve free from presumably restricting tissues in its passage through the pudendal canal. Thus far, such procedures have met with limited success and debatable results in most cases.

Based on cadaveric studies, O’Bichere et al.68 recommend a surgical approach to the pudendal nerve that combines review of surface landmarks for anomalies with exposure of the gluteus maximus muscle, sacrotuberous ligament, and pudendal neurovascular bundle.

The glands of the anal canal are prone to infection. This can result in the formation of fistulous tracts to the skin or localized abscesses in the ischioanal fossae.

The rich anastomoses between the portal venous system and the systemic system can increase portal pressure. A reversal of flow within the superior rectal vein can cause dilation of submucosal tributaries to the middle rectal and inferior rectal veins and lead to hemorrhoidal varices.

Hemorrhoids above the pectinate line are called internal hemorrhoids. Because sensory fibers from this region are carried by pelvic splanchnic nerves, and because most of the sensory receptors are sensitive only to pressure, sensation from internal hemorrhoids is poorly perceived and poorly localized. Thus, such hemorrhoids can be large and dangerous, resulting even in anemia from loss of blood.

Hemorrhoids below the pectinate line are called external hemorrhoids. External hemorrhoids produce pain and other disagreeable sensations which are perceived acutely and localized with considerable precision.

There are four anatomic types of rectal fistulas: intersphincteric, transsphincteric, suprasphincteric, and extrasphincteric.69


– Intersphincteric fistulas are the most common (70%). The usual pathway is to the anal margin (Fig. 28-58); a subcutaneous tract is possible. Occasionally, the pathway is upward into the rectal wall and into the rectal ampulla (Fig. 28-59).

– Transsphincteric fistulas account for approximately 25 percent of rectal fistulas (Fig. 28-60). This fistula extends through the external sphincter to the ischioanal fossa and the skin.

– Suprasphincteric fistulas comprise about 4 percent of all rectal fistulas (Fig. 28-61). Their pathway is peculiarly convoluted upward into the intersphincteric space, over the puborectalis muscle, and downward into the ischioanal fossa to the skin.

– Extrasphincteric fistulas (Fig. 28-62) constitute only 1 percent of rectal fistulas. The pathway is from the perineal skin to the ischioanal fossa, through the levator ani, and to the rectal wall.

Rectal fistulas may also be divided into the following two types:


– Anorectal, involving only the perianal tissues

– Ischioanal, passing through the ischioanal space, often in a complicated course

Goodsall-Salmon’s rule of fistulas70 (Fig. 28-63), which relates the internal location of the fistula to its external opening, must be learned:


– If the external opening of the fistula is anterior to an imaginary transverse line across the anus, most likely the tract of the fistula is a straight line terminating into the anal canal.

– If this external opening is located more than 3 cm anterior to the line, the tract may curve posteriorly, terminating in the posterior midline.

– In an opening posterior to the transverse line, the tract will most likely curve, terminating into the posterior wall of the anal canal.

The subcutaneous and the superficial external sphincters of the anal canal can be divided with impunity. One must exercise care when exploring the deep external sphincter and the puborectalis.

If fistulas requiring excision develop, they will be near the anal verge. If a fistula is deep, the seton procedure is the treatment of choice. If the fistula is simple and not deep, the fistulous tract can be completely excised, leaving the wound open.

Most fistulas in ano are midline posterior.

Episiotomy can be accomplished by a posterior midline incision. Incise the posterior vaginal wall, skin of the perineum, perineal body, and superficial external ani sphincter. According to Signorello et al.,71 midline episiotomy is not effective in protecting the perineum and sphincters during childbirth and may impair anal continence. A posterolateral incision will incise the vaginal wall, skin of the ischioanal fossa, bulbospongiosus muscle, vestibular bulb, superficial transverse perineus muscle, posterior edge of the urogenital diaphragm, and perhaps the pubococcygeus muscle. If careful repair of all anatomic entities involved is not carried out, then a degree of relaxation of the perineal floor and rectocele or cystocele, or both, may develop.

Fig. 28-58.

Intersphincteric fistula. (From Parks AG, Thomson JPS. Abscess and fistula. In: Thompson JPS, Nicholls RJ, Williams CR (eds). Colorectal Disease. New York: Appleton-Century-Croft, 1981; with permission.)

Fig. 28-59.

Intersphincteric fistula with opening into rectum. (From Parks AG, Thomson JPS. Abscess and fistula. In: Thompson JPS, Nicholls RJ, Williams CR (eds). Colorectal Disease. New York: Appleton-Century-Croft, 1981; with permission.)

Fig. 28-60.

Transsphincteric fistula. (From Parks AG, Thomson JPS. Abscess and fistula. In: Thompson JPS, Nicholls RJ, Williams CR (eds). Colorectal Disease. New York: Appleton-Century-Croft, 1981; with permission.)

Fig. 28-61.

Suprasphincteric fistula. (From Parks AG, Thomson JPS. Abscess and fistula. In: Thompson JPS, Nicholls RJ, Williams CR (eds). Colorectal Disease. New York: Appleton-Century-Croft, 1981; with permission.)

Fig. 28-62.

Extrasphincteric fistulas. Left, Follows perforation of rectum due to foreign body. Right, Follows upward extension into rectum from ischioanal (ischiorectal) fossa, perhaps a result of injudicious use of fistula probe. (From Parks AG, Thomson JPS. Abscess and fistula. In: Thompson JPS, Nicholls RJ, Williams CR (eds). Colorectal Disease. New York: Appleton-Century-Croft, 1981; with permission.)

Fig. 28-63.

Rectal fistulas. Tracts illustrate Goodsall-Salmon’s rule (see text). (Modified from Imbembo AL, Zuidema GD. Anal canal and rectum. In: Nardi GL, Zuidema GD (eds). Surgery: Essentials of Clinical Practice (4th ed). Boston: Little, Brown, 1982, pp. 579-580; with permission.)

Anatomic Complications

The anatomic complications of the perineum are the complications of surgery of the several anatomic entities that are related to the perineum.


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