UEU-co logo

//FUNCTIONAL ANATOMICAL DIVISIONS

FUNCTIONAL ANATOMICAL DIVISIONS

Current understanding of the functional anatomy of the liver is based on Couinaud’s division of the liver into eight (subsequently nine) functional segments, based upon the distribution of portal venous branches and the location of the hepatic veins in the parenchyma (Couinaud 1957). Further understanding of the intrahepatic biliary anatomy, especially of the right ductal system, was enhanced by contributions from Hjortsjo (1948) and Healey & Schroy (1953) using the biliary system as the main guide for division of the liver (Fig. 68.4).

  

Fig. 68.4  The fissures and sectors of the liver. (Right lateral = right posterior; right medial = right anterior.)

The liver is divided into four portal sectors by the four main branches of the portal vein. These are right lateral, right medial, left medial and left lateral (sometimes the term posterior is used in place of lateral and anterior in place of medial). The three main hepatic veins lie between these sectors as intersectorial veins. These intersectoral planes are also called portal fissures (scissures). The fissures containing portal pedicles are called hepatic fissures. Each sector is sub-divided into segments (usually two) based on their supply by tertiary divisions of the vascular biliary sheaths.

Fissures of the liver

Knowledge of the fissures of the liver is essential for understanding liver surgery. Three major fissures, not visible on the surface, run through the liver parenchyma and harbour the three main hepatic veins (main, left and right portal fissures). Three minor fissures are visible as physical clefts of the liver surface (umbilical, venous and fissure of Gans).

Main portal fissure

The main fissure extends from the tip of the gallbladder back to the midpoint of the inferior vena cava and contains the middle (main) hepatic vein. It separates the liver into right and left hemi-livers. Segments V and VIII lie to the right and segment IV to the left of the fissure.

Left portal fissure

The left fissure divides the left hemi-liver into medial (anterior) and lateral (posterior) sectors. It extends from the mid point of the anterior edge of the liver between the falciform ligament and the left triangular ligament to the point which marks the confluence of the left and middle hepatic veins. It contains the left hepatic vein and separates the left anterior and left posterior sectors: segment III lies anteriorly and segment II posteriorly.

Right portal fissure

The right portal fissure divides the right hemi-liver into lateral (posterior) and medial (anterior) sectors. The plane of the right fissure is the most variable amongst the main fissures and runs approximately diagonally through the gross right lobe from the lateral end of the anterior border to the confluence of the left and middle hepatic veins. The fissure divides the right anterior sector to its left (segments V and VIII) from the right posterior sector to its right (segments VI and VII), and contains the right hepatic vein. The right fissure marks the thickest point of liver parenchyma which is commonly transected during liver resection.

Umbilical fissure

The umbilical fissure separates segment III from segment VI within the left anterior sector and contains a main branch of the left hepatic vein (the umbilical fissure vein). It is marked by the attachment of the falciform ligament and sometimes covered by a ridge of liver tissue extending between the segments: it is often avascular and can be divided safely with diathermy during a surgical approach. It contains the umbilical portion of the left portal vein and the final divisions of the left hepatic duct and the left hepatic artery branches. The umbilical portion of the left portal vein is an important landmark: access to this vein and mobilization of the left portal vein are essential steps in surgery for hilar cholangiocarcinoma. A knowledge of the arrangement of the portal vein, hepatic artery and bile duct within the umbilical fissure is also essential when splitting the liver for an adult and paediatric recipient and for live donor liver transplantation for a child recipient.

Venous fissure

The venous fissure is a continuation of the umbilical fissure on the under surface of the liver and contains the ligamentum venosum. It lies between the caudate lobe and segment IV. The deeper continuation of this plane is the dorsal fissure.

Fissure of Gans

The fissure of Gans lies on the undersurface of the right lobe of the liver behind the gallbladder fossa. It often contains the portal pedicle to the right posterior sector and is thought to correspond to the right fissure as it relates to the separation of the sectors of the liver.

Sectors and segments of the liver

Sectors

The sectors of the liver are made up of between one and three segments: right lateral sector = segments VI and VII; right medial sector = segments V and VIII; left medial sector = segments III and IV (and part of I); left lateral sector = segment II (Fig. 68.5). Segments are numbered in an ante-clockwise spiral centered on the portal vein with the liver viewed from beneath, starting with segment I up to segment VI, and then back clockwise for the most cranial two segments VII and VIII (Fig. 68.6).

  

Fig. 68.5  Segments of the liver (after Couinaud). A, superior view; B, posterior view; C, anterior view; D, inferior view. The segments are sometimes referred to by number (name) – I (caudate) (sometimes subdivided into left and right parts called segment IX); II (left lateral superior); III (left medial inferior); IV (left medial superior) (sometimes subdivided into superior and inferior parts); V (right medial inferior); VI (right lateral inferior); VII (right lateral superior); VIII (right medial superior).

  

Fig. 68.6  Segments of the liver seen on axial CT scan. A, Contrast enhanced CT shows the left (L), middle (M), and right (R) hepatic veins at the superior aspect of the liver marking the left main and right portal fissures. B, Inferior to this the caudate lobe (segment I) lies between the inferior vena cava (IVC) and the main portal vein (PV). The left portal vein (LPV) separates segment II superiorly from segment III inferiorly. C, The right portal vein (RPV) divides segments V and VI inferiorly (C) from segments VII and VIII superiorly (B).

Segment I

Segment I corresponds to the anatomical caudate lobe and lies posterior (dorsal) to segment IV with its left half directly posterior to segments II and II and its medial half surrounded by major vascular branches. The Glissonian sheaths to segment I arise from both right and left main sheaths: the segment therefore receives vessels independently from the left and right portal veins and hepatic arteries, and it drains independently into the inferior vena cava by multiple small branches (referred to as the lower group). They nearly always arise in the lower and occasionally from the middle third, but never from the upper third of the segment. The bile ducts draining the segment are closely related to the confluence of the right and left hepatic ducts such that excision of central bile duct tumours usually requires removal of segment IV.

Segment II

Segment II is the only segment in the left lateral sector of the liver and lies postero-lateral to the left fissure. It often has only one Glissonian sheath and drains into the left hepatic vein. Rarely, a separate vein drains directly into the inferior vena cava.

Segment III

Segment III lies between the umbilical fissure and the left fissure and is often supplied by one to three Glissonian sheaths: it drains into the left hepatic vein. The vein of the falciform ligament can provide an alternative drainage route for segment III.

Segment IV

Segment IV lies between the umbilical fissure and the main fissure, anterior to the dorsal fissure and segment I. Segment IV is supplied by three to five Glissonian sheaths, of which the majority arise in the umbilical fissure; their origins are often close to those that supply to segments II and III. Occasionally segment IV is supplied by branches from the main left pedicle. The main venous drainage segment is into the middle hepatic vein; the segment can also drain into the left hepatic vein through the vein of the falciform ligament.

Segment V

Segment V is the inferior segment of the right medial sector and lies between the middle and the right hepatic veins. Its size is variable, as are the number of Glissonian sheaths that supply it. Venous drainage is into the right and middle hepatic veins.

Segment VI

Segment VI forms the inferior part of the right lateral sector posterior to the right portal fissure. It is often supplied by two to three branches from the right posterior Glisson’s sheath, but occasionally the Glisson’s sheath to segment VI can arise directly from the right pedicle. Venous drainage is normally into the right hepatic vein, but may be via the right inferior hepatic vein directly into the inferior vena cava.

Segment VII

Segment VII forms the superior part of the posterior sector and lies behind the right hepatic vein. The sheaths to segment VII are often single. The venous drainage is into the right hepatic vein; occasionally the segment can drain through the right middle hepatic vein directly into the inferior vena cava.

Segment VIII

Segment VIII is the superior part of the right anterior sector. The right anterior sectoral sheaths end in segment VIII and supply it after giving off branches to segment V. The venous drainage is to the right and middle hepatic veins.

Segment IX

Segment IX is a recent subdivision of segment I, and describes that part of the segment that lies posterior to segment VIII.

Supports of the liver

The liver is stabilized and maintained in its position in the right upper quadrant of the abdomen by both static and dynamic factors. Richelme & Bourgeon (1973) suggested a three-tier classification of the anatomical factors: the suspensory attachments at the posterior abdominal wall to the inferior vena cava, hepatic veins, coronary and triangular ligaments (primary factors); the support provided by the right kidney, right colonic angle and duodenopancreatic complex (secondary factors); the attachment to the anterior abdominal wall and diaphragm by the falciform ligament (tertiary factors).

The surgical implications of these different factors are important for traumatologists in terms of achieving a better understanding of the pathophysiology of liver trauma. The inferior vena cava and the supra-hepatic veins, especially the right hepatic vein, appear to be the most important anatomical structures that support the bulk of the liver. Other factors which are responsible for the maintenance of the position of the liver within the abdominal cavity include positive intra-abdominal pressure and the movement of the diaphragm during respiration.

Peritoneal attachments and ligaments of the liver

The liver is attached to the anterior abdominal wall, diaphragm and other viscera by several ligaments which are formed from condensations of the peritoneum.

Falciform ligament

The liver is attached in front to the anterior abdominal wall by the falciform ligament. The two layers of this ligament descend from the posterior surface of the anterior abdominal wall and diaphragm and turn onto the anterior and superior surfaces of the liver. On the dome of the superior surface, the right leaf runs laterally and is continuous with the upper layer of the coronary ligament. The left layer of the falciform ligament turns medially and is continuous with the anterior layer of the left triangular ligament. The ligamentum teres, which represents the obliterated left umbilical vein, runs in the lower free border of the falciform ligament and continues into a fissure on the inferior surface of the liver. In fetal life the left umbilical vein opens into the left portal vein: it is supposed to be obliterated in adult life, but frequently remains partially patent. This lumen may open up in conditions such as portal hypertension to form a collateral channel. The ligamentum teres has importance in abdominal surgery for several reasons. It is quite often divided in upper abdominal surgery to optimize access to the upper abdominal viscera or as the first step in the mobilization of the liver. The ligament is vascularized by numerous arterial branches, mainly from the segment IV artery, and these form an anastomotic connection with the branches of the internal thoracic artery: it is therefore important to ligate or coagulate the ligament during its division. The ligamentum teres is a landmark and guide to the segment III hepatic duct used in hepatocojejunostomy formation, and to the left portal vein lying in the umbilical fissure during creation of a mesentericoportal shunt.

Coronary ligament

The coronary ligament is formed by the reflection of the peritoneum from the diaphragm onto the posterior surfaces of the right lobe of the liver. A large triangular area of liver devoid of peritoneal covering, the ‘bare area’ of the liver, is defined between the two layers of the coronary ligament. Here the liver is attached to the diaphragm by areolar tissue and is in continuity inferiorly with the anterior pararenal space. The coronary ligament is continuous on the right with the right triangular ligament. On the left, the two layers become closely applied, and form the left triangular ligament. The upper layer of the coronary ligament is reflected superiorly onto the inferior surface of the diaphragm and inferiorly onto the right and superior surface of the liver. The lower layer of the coronary ligament is reflected inferiorly over the right suprarenal gland and right kidney, and superiorly onto the inferior surface of the liver. Surgical division of the right triangular and coronary ligaments allows the right lobe of the liver to be brought forward, and exposes the lateral aspect of the inferior vena cava behind the liver.

Triangular ligaments

The left triangular ligament is a double layer of peritoneum which extends to a variable length over the superior border of the left lobe of the liver. Medially the anterior leaf is continuous with the left layer of the falciform ligament and the posterior layer is continuous with the left layer of the lesser omentum. The left triangular ligament lies in front of the abdominal part of the oesophagus, the upper end of the lesser omentum and part of the fundus of the stomach. Division of the left triangular ligament allows the left lobe of the liver to be mobilized for exposure of the abdominal oesophagus and crura of the diaphragm. The left triangular ligament is an important stabilizing factor for the left lobe in operations involving removal of the right lobe of the liver. Its division will result in the left lobe being unstable to the extent that it can rotate and displace into the space vacated under the right hemidiaphragm: this extreme degree of rotation can compromise the venous outflow of the liver with consequent liver dysfunction. If it is divided, the left triangular ligament must be fixed at the end of the surgery, in addition to fixing back the falciform ligament.

The right triangular ligament is a short structure which lies at the apex of the ‘bare area’ of the liver and is continuous with the layers of the coronary ligament.

Lesser omentum

The lesser omentum is a fold of peritoneum which extends from the lesser curve of the stomach and proximal duodenum to the inferior surface of the liver. Its attachment to the inferior surface of the liver is L-shaped. The vertical component follows the line of the fissure for the ligamentum venosum, the fibrous remnant of the ductus venosus. More inferiorly the attachment runs horizontally to complete the L in the porta hepatis. At its upper end, the superior layer of the lesser omentum is continuous on the left with the posterior layer of the left triangular ligament, and the inferior layer is continuous on the right with the coronary ligament as it encloses the inferior vena cava. At its lower end, the two layers diverge to surround the structures of the porta hepatis. A thin fibrous condensation of fascia usually runs from the medial end of the porta hepatis into the fissure in the inferior surface which contains the ligamentum teres. This fascia is continuous with the lower border of the falciform ligament when the ligamentum teres re-emerges at the inferior border of the liver. Care should be taken when dividing the lesser omentum, because an aberrant left hepatic artery may run in the medial end: when present, it invariably extends to the liver at the base of the umbilical fissure, and may be identified by a pulsation in the lesser omentum close to the umbilical fissure.

Ligamentum venosum

The ligamentum venosum represents the obliterated venous connection that existed between the left portal vein and the left hepatic vein in fetal life. It is used as a guide and aid to control the left hepatic vein extrahepatically during surgery. By dividing the ligament close to its insertion into the left hepatic vein and retracting it laterally, the angle between the left and the middle hepatic veins, required for dissection and control of the left hepatic vein, may be accessed.

Porta hepatis, hepatoduodenal ligament and hilar plate

The porta hepatis is a deep fissure on the inferior surface of the liver. It is situated between the quadrate lobe in front and the caudate process behind, and contains the portal vein, hepatic artery and hepatic nervous plexuses as they ascend into the parenchyma of the liver, and the right and left bile ducts and some lymph vessels as they emerge from the liver. The hepatic ducts lie anterior to the portal vein and its branches, and the hepatic artery with its branches lies between the two (Fig. 68.7). All these structures are enveloped in the perivascular fibrous capsule, the hepatobiliary capsule of Glisson, a sheath of loose connective tissue which surrounds the vessels as they course through the portal canals in the liver and is also continuous with the fibrous hepatic capsule. The dense aggregation of vessels, supporting connective tissue, and liver parenchyma just above the porta hepatis is often referred to as the ‘hilar plate’ of the liver (Fig. 68.8). Understanding of the concept of hilar plate is important in surgical approaches to the hilar structures. Division or lowering of the hilar plate are essential for surgical access to the left hepatic duct. The hepatic artery, bile duct and portal vein extend from the porta hepatis towards the duodenum in the free edge of the hepatoduodenal ligament, which forms the anterior boundary of the epiploic foramen. Rapid control of the vessels entering the porta hepatis can be obtained by dividing the lesser omentum to the left of these structures and passing a tape around them from left to right through the epiploic foramen (a ‘Pringle’ manoeuvre).

  

Fig. 68.7  Cross-section of the structures at the porta hepatis.

  

Fig. 68.8  Axial CT of the porta hepatis. The hepatic ducts lie anteriorly, the portal vein posteriorly, and hepatic artery between the two.

The left hepatic duct remains extrahepatic as it runs down to the bifurcation along the base of segment IV (the quadrate lobe). This extrahepatic length of duct is particularly useful when performing high biliary duct reconstructions where a length of jejunum is anastomosed to form a biliary-enteric bypass, to treat strictures of the common hepatic duct.

Glisson’s sheath

Glisson’s capsule condenses around the branches of the portal triad structures as Glissonian sheaths as they enter the liver parenchyma and extends as far the individual segments of the liver. This arrangement facilitates surgical control of both the main right and left pedicles of the liver as well as all the structures (biliary, autonomic and lymphatic elements) that supply individual sectors and segments in liver complex resectional surgery.

Leave a Reply


Time limit is exhausted. Please reload the CAPTCHA.

Categories

apply_now Pepperstone Group Limited