Right Ectopic Ureter with a Duplicated Collecting System
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Right Ectopic Ureter with a Duplicated Collecting System |
Diagnosis
The renal ultrasound shows a dilated right upper pole pelvis (Fig. 1). Bladder ultrasound reveals right hydroureter posterior to the bladder (Fig. 2), and the excretory urogram shows the characteristic lateral displacement of a lower collecting system with a dilated, functionless upper pole pelvis. (Fig. 3). The abdominal CT demonstrates a nonfunctioning right upper pole renal unit with a dilated tortuous ureter passing behind the bladder (Fig. 4). No reflux was appreciated on the voiding cystourethrogram. Cystoscopy revealed an ectopic uretral orifice distal to the right uretral orifice. A retrograde pyelogram was attempted, but was unsuccessful. The patient underwent an uneventful right upper pole heminephrectomy with partial ureterectomy. She is now free of urinary tract infections.
Epidemiology
Ectopic ureter occurs three times more commonly in females than in males. More than 80% of female ectopic ureters involve duplicated systems, while the majority of male ectopic ureters are of a single system.1 The most common extravesical sites in the female are the urethra and the vestibule while the posterior urethra is the most common site in the male.2
Embryology
Before the mesonephric duct is absorbed into the urogenital sinus (UGS), it gives off a single uretral bud. The common excretory duct is the segment of mesonephric duct between the uretral bud and the urogenital sinus. As the common excretory duct is absorbed into the UGS, the uretral orifice migrates cephalad and laterally while the mesonephric duct rotates caudally and medially. In the male, the meatus of the mesonephric duct becomes the ejaculatory duct.
Complete ureteral duplication occurs when the mesonephric duct gives off a second ureteral bud. The ureteral bud closest to the UGS becomes the lower pole ureter and the bud further away becomes the upper pole ureter. As the common excretory duct is absorbed, the lower pole ureteral orifice migrates cephalad and laterally; however, the upper pole ureteral orifice migrates caudally and medially to obey the Weigert-Meyer law.3,4 Because the lower pole ureteral bud is absorbed more rapidly, the detrusor submucosal tunnel becomes short. This short submucosal tunnel predisposes the lower pole ureter to reflux. In contrast, the upper pole ureteral bud is absorbed slowly, resulting in a long submucosal tunnel. In males, the upper pole ureteral orifice may insert into the posterior urethra, prostatic utricle, seminal vesical, ejaculatory duct, or vas deferens. In females, the upper pole ureter may insert into the urethra, vestibule, vagina, cervix, uterus, Gartner's duct, or a urethral diverticulum.
A rare exception to the Weigert-Meyer law occurs when there is an early division of a single ureteral bud. Early fusion of the ureteral bud before it leaves the mesonephric duct to meet the metanephric blastema will result in a complete duplication. After the absorption of a common excretory duct, the common base will be absorbed into the UGS without rotation of ureteral orifices.5
Symptoms
Approximately half of all affected females experience persistent urinary incontinence because the ectopic ureter drains distal to the external sphincter. Males may have symptoms of urinary obstruction or infection. When the ectopic ureter drains into the posterior urethra, males may experience urinary frequency and urgency but not incontinence. If the seminal tract is involved, symptoms may not appear until onset of sexual activity, and include prostatitis, epididymitis or hematospermia.
Radiologic Studies
Ultrasound is the initial imaging modality of choice because it is inexpensive, non-invasive and highly sensitive. The most important finding on ultrasound is of two central echo complexes with intervening parenchyma. Ultrasound can also identify the associated abnormal hydroureter and trace it down to the bladder. Upper pole hydronephrosis is usually caused by an ectopic upper pole ureter causing distal obstruction. Lower pole hydronephrosis is caused by either reflux or ureteropelvic junction obstruction.6 Ultrasound diagnosis may be difficult if the upper pole renal unit is small and nonfunctional. However, nuclear scan will demonstrate functioning renal tissue, and may show two recognizable collecting systems on the same side.
Excretory urogram displays the characteristic findings of duplicated renal units. When the upper system is very dilated, the functioning lower system is displaced inferiorly and laterally -- the classic "drooping lily" sign. The duplicated kidney is longer than the normal contralateral kidney, and its calyces are asymmetrical. Also, there is differential parenchymal thickness between the two poles.
Abdominal CT scan can be helpful in difficult diagnostic situations. The area between the two collecting systems is devoid of any major vessels or collecting system elements. When a transverse cut is made at this interface, only renal parenchyma is visible. This "faceless kidney" appearance is diagnostic of a duplicated collecting system.7
A voiding cystourethrogram is essential for all patients suspected of having a duplicated collecting system with an ectopic ureter. The lower pole ureter is more likely to reflux due to its short submucosal tunnel. Vesicoureteral reflux is the most common abnormality associated with complete ureteral duplication.
An ectopic ureteral orifice in the urethra is not particularly difficult to localize cystoscopically. However, it can be extremely difficult to localize in the vagina. Usually it is located in the anterior and lateral portion of the vagina in the region of the Gartner's duct.
Treatment
In the majority of cases, the affected renal unit is developmentally abnormal and severely damaged by pyelonephritis. Excision of the abnormal renal unit and affected ureter is generally curative. In most cases the distal ureter is left in situ. Aggressive dissection to remove the entire ureter is rarely necessary and carries additional morbidity. Partial nephrectomy and ureterectomy is performed for poorly functioning or non-functioning upper pole renal units. Ureteroneocystostomy or pyelopyelostomy with distal ureterectomy is the usual choice of therapy for a renal unit with good function.
References
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