//URETER

URETER

The ureters are two muscular tubes whose peristaltic contractions convey urine from the kidneys to the urinary bladder (Fig. 74.9). Each measures 25–30 cm in length, is thick-walled and narrow, and is continuous superiorly with the funnel-shaped renal pelvis. Each descends slightly medially, anterior to psoas major, and enters the pelvic cavity where it curves initially laterally, then medially, to open into the base of the urinary bladder. The diameter of the ureter is normally 3 mm, but is slightly less at its junction with the renal pelvis, at the brim of the lesser pelvis near the medial border of psoas major, and where it runs within the wall of the urinary bladder, which is its narrowest part. These are the commonest sites for renal stone impaction.

RELATIONS

In the abdomen the ureter descends posterior to the peritoneum on the medial part of psoas major, which separates it from the tips of the lumbar transverse processes. During surgery on intraperitoneal structures, the ureter can be tented up as the peritoneum is drawn anteriorly, resulting in inadvertent ureteric injury. Anterior to psoas major it crosses in front of the genitofemoral nerve and is obliquely crossed by the gonadal vessels (Fig. 74.19). It enters the lesser pelvis anterior to either the end of the common iliac vessels or at the origin of the external iliac vessels (Fig. 74.20).

  

Fig. 74.19  Relations of lower ureter. A, Male pelvis. B, Female pelvis.
(From Drake, Vogl and Mitchell 2005.)

  

Fig. 74.20  Relations of male lower right ureter.
(By permission from Walsh PC, Retik AB, Vaughan ED et al (eds) 2002 Campbell’s Urology, 8th edn. Philadelphia: Saunders.)

The inferior vena cava is medial to the right ureter while the left ureter is lateral to the aorta. The inferior mesenteric vein has a long retroperitoneal course lying close to the medial aspect of the left ureter.

At its origin the right ureter is usually overlapped by the descending part of the duodenum. It descends lateral to the inferior vena cava, and is crossed anteriorly by the right colic and ileocolic vessels. Near the superior aperture of the lesser pelvis it passes behind the lower part of the mesentery and terminal ileum. The left ureter is crossed by the gonadal and left colic vessels (see Fig. 74.24). It passes posterior to loops of jejunum and sigmoid colon and its mesentery in the posterior wall of the intersigmoid recess.

  

Fig. 74.24  Arterial supply of the left ureter. The proximal part takes its blood supply medially, and the distal part is supplied laterally.
(By permission from Walsh PC, Retik AB, Vaughan ED et al (eds) 2002 Campbell’s Urology, 8th edn. Philadelphia: Saunders.)

In the pelvis the ureter lies in extraperitoneal areolar tissue (see Fig. 75.3). At first it descends posterolaterally on the lateral wall of the lesser pelvis along the anterior border of the greater sciatic notch. Opposite the ischial spine it turns anteromedially into fibrous adipose tissue above levator ani to reach the base of the bladder. On the pelvic side-wall it is anterior to the internal iliac artery and the beginning of its anterior trunk, posterior to which are the internal iliac vein, lumbosacral nerve and sacroiliac joint. Laterally it lies on the fascia of obturator internus. It progressively crosses to become medial to the umbilical, inferior vesical, and middle rectal arteries.

In males, the pelvic ureter hooks under the vas deferens (Fig. 74.21), then passes in front of and slightly above the upper pole of the seminal vesicle to traverse the bladder wall obliquely before opening at the ipsilateral trigonal angle. Its terminal part is surrounded by tributaries of the vesical veins. In females, the pelvic part at first has the same relations as in males, but anterior to the internal iliac artery it is immediately behind the ovary, forming the posterior boundary of the ovarian fossa (see Ch. 77). In the anteromedial part of its course to the bladder it is related to the uterine artery, uterine cervix and vaginal fornices. It is in extraperitoneal connective tissue in the inferomedial part of the broad ligament of the uterus where it may be damaged during hysterectomy. In the broad ligament, the uterine artery is anterosuperior to the ureter for 2.5 cm and then crosses to its medial side to ascend alongside the uterus. The ureter turns forwards slightly above the lateral vaginal fornix and is generally 2 cm lateral to the supravaginal part of the uterine cervix in this location. It then inclines medially to reach the bladder, with a variable relation to the anterior aspect of the vagina. As the uterus is commonly deviated to one side, one ureter, usually the left, may be more extensively apposed to the vagina, and may cross the midline.

  

Fig. 74.21  Posterior aspect of the male urogenital organs, showing relationship of the lower ureter to the vas deferens and seminal vesicles.
(From Sobotta 2006.)

The distal 1–2 cm of each ureter is surrounded by an incomplete collar of non-striated muscle, which forms a sheath (of Waldeyer). The ureters pierce the posterior aspect of the bladder and run obliquely through its wall for a distance of 1.5–2.0 cm before terminating at the ureteric orifices (see Fig. 75.5B). This arrangement is believed to assist in the prevention of reflux of urine into the ureter, since the intramural ureters are thought to be occluded during increases in bladder pressure at the time of micturition. There is no evidence of a classic ureteral sphincter mechanism in man. The longitudinally oriented muscle bundles of the terminal ureter continue into the bladder wall and at the ureteric orifices become continuous with the superficial trigonal muscle. In the distended bladder, in both sexes, the ureteric openings are usually 5 cm apart, and 2.5 cm apart when the bladder is empty.

Duplex ureters

In 1 in 125 individuals, two ureters drain the renal pelvis on one side; this is termed a duplex system (Fig. 74.22). Bilateral duplex ureters occur in approximately 1 in 800 cases. The duplex ureters derive from two ureteric buds arising from the mesonephric duct. They are contained in a single fascial sheath and may fuse at any point along their course or may be separate until they insert through separate ureteric orifices into the bladder. Care must be taken not to compromise the blood supply of the second ureter when excising or reimplanting a single ureter of a duplex.

  

Fig. 74.22  Intravenous urogram showing bilateral duplex ureters and bilateral ureteroceles. Note that the ureters cross during their course. The right ureterocele can be clearly seen producing a halo appearance within the bladder surrounding the lower ureter. 1. Contrast within lower moiety of collecting system. 2. ‘Cobra’s head’ halo around lower ureter showing ureterocele. 3. Contrast within upper moiety of collecting system.

The ureter from the upper pole of the kidney (the longer ureter) inserts more medially and caudally in the bladder than the ureter from the lower pole (the shorter ureter). This reflects the embryological development of the ureter: the ureteric bud which is initially more proximal on the mesonephric duct has a shorter time to be pulled cranially in the bladder and so it inserts more distally in the mature bladder. The ureter from the lower pole has a shorter intramural course than the longer ureter and is prone to reflux.

Ectopic ureters

Single ureters, and more commonly the longer ureter of a duplex system, can insert more caudally and medially than normal in some individuals. In the male the ureter can insert at the bladder neck or posterior urethra, or rarely into the seminal vesicle, but it always inserts cranial to the external urethral sphincter. In the female, ectopic insertion can be distal to the external urethral sphincter in the urethra, or into the vagina, resulting in persistent childhood incontinence.

Ureteroceles

A ureterocele is a cystic dilatation of the lower end of the ureter: the ureteric orifice is covered by a membrane which expands as it is filled with urine and then deflates as it empties. Ureteroceles can vary in size, and although usually they have no influence on ureteric drainage they can be a cause of obstruction in the ureter and pelvicalyceal system more proximally. They usually do not cause bladder outflow obstruction except for the rare prolapsing ureterocele. Prolapsing ureteroceles, though small, prolapse from their position around the uretero-vesical junction region in to the urethra, causing intermittent bladder outflow obstruction. They are identified antenatally with ultrasound. In adults, ureteroceles tend to be bilateral and small and often found incidentally when the urinary tract is being imaged in the investigation of a coincidental pathology. Radiologically they classically result in a ‘cobra-head’ halo around the ureteric orifice following administration of contrast on intravenous urography (Fig. 74.22).

Retrocaval ureter

A persistence of the posterior cardinal vein, associated with high confluence of the right and left common iliac veins or a double inferior vena cava, may result in a retrocaval (or circumcaval) ureter which passes behind the inferior vena cava, usually at the level of the inferior edge of the third part of the duodenum, before it emerges in front of it to pass from medial to lateral. Retrocaval ureter occurs in 1 in 1500 individuals. Most commonly it has no clinical sequelae although it can result in upper ureteric obstruction (Fig. 74.23).

  

Fig. 74.23  Intravenous urogram showing a classical retrocaval (or circumcaval) ureter. A degree of obstruction has resulted in a markedly dilated upper ureter. The ureter passes cranially, medially and then caudally, and can be followed into the pelvis. 1. Contrast within dilated collecting system of right kidney and upper ureter. 2. Contrast within ureter turning behind inferior vena cava. 3. Contrast within normal calibre ureter seen below the obstruction. 4. Contrast within normal collecting system of left kidney and upper ureter.

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