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Duplicated Ureter or Duplex Kidney: Symptoms and Diagnosis

Definition of Duplex Kidney and Ureteral Duplication

Ureteral duplication, also called a duplex kidney, is an anatomic variant of the ureter and pyelocalyceal system with considerable variability [variants of the duplex kidney] (EAU guideline).

Complete ureteral duplication:

Complete duplication with two ureters, two renal pelves, and two ureteral orifices.

Ureter fissus or bifid ureter:

Incomplete ureteral duplication with a common ureteral orifice.

Bifid renal pelvis:

Duplication of the renal pelvis, with the two pelves joining at the ureteropelvic junction.

Different variants of ureteral duplication: complete ureteral duplication (left), ureter fissus (center), and bifid renal pelvis (right).

Inverted Y ureteral duplication:

Two separate distal ureteral buds, each with its own orifice, fuse cranially to form a common ureter. Very rare.

Ureteral triplication:

Three independent ureters with three orifices, or incomplete ureteral triplication with two or one orifice. Very rare.

Epidemiology of the Duplex Kidney

Prevalence is 0.7–1%. Women are affected more often.

Etiology of the Duplex Kidney

Two ureteric buds:

Complete ureteral duplication results from two ureteric buds arising from the mesonephric duct (Wolffian duct). The buds form two ureters and a duplex kidney within a common renal capsule. As the ureteric buds and the orifice plate rotate 180 degrees, the lateral (cranial) ureter drains the lower pole system, and the medial (caudal) ureter drains the upper pole system. This relationship is called the Meyer-Weigert rule.

Division of the ureteric bud:

Incomplete ureteral duplications (bifid ureter, bifid pelvis) are caused by a division of a single ureteric bud on its way to the metanephric blastema.

Pyelocalyceal system of the duplex kidney:

Compared with a single kidney, which has 8–9 calyces, a duplex kidney has 11–12 calyces. The upper pole system is smaller, with an average of 3–4 calyces.

Associated malformations:

Associated malformations include vesicoureteral reflux into the lower pole system, ureteropelvic junction obstruction of the lower pole system, an ectopic ureteral orifice of the upper pole system, a ureterocele of the upper pole ureter, and renal dysplasia or hypoplasia, particularly of the upper pole system.

Pathophysiology:

Associated malformations in patients with complete ureteral duplication increase the risk of urinary tract infections, hydronephrosis, urinary incontinence, and nephrolithiasis.

Signs and Symptoms of a Duplex Kidney

Without associated malformations, ureteral duplication usually causes no symptoms. Possible symptoms include urinary tract infections, fever, flank pain, and urinary incontinence.

Diagnostic Workup

Ultrasound imaging:

Ultrasound may be normal when there are no associated malformations. A duplex kidney may be suspected when a prominent parenchymal column in the midportion separates two renal sinuses (fig. ultrasound of a duplex kidney). Detection is easier when a ureterocele or hydronephrosis is present; the upper pole system is often affected (fig. ultrasound of a duplex kidney with hydronephrosis of the upper pole system).

Ultrasound imaging of a duplex kidney.

Ultrasound imaging of a duplex kidney with hydronephrosis of the upper pole system due to a ureteral stone.

Intravenous urography:

Excretory urography has largely been replaced by cross-sectional imaging. Ureteral duplication is often an incidental finding during the diagnostic workup of other diseases [fig. duplex kidney in IVU]. If the upper renal moiety has poor function, it may not be visualized with contrast, or the upper pole ureter may opacify only on delayed images. A smaller number of opacified calyces and a greater distance between the renal outline and the spine suggest a nonopacified upper pole system (fig. dropping lily sign). The lower pole ureter follows a tortuous course. A ureterocele may sometimes be seen in the bladder.

Left-sided ureteral duplication on intravenous urography: both renal moieties are well functioning and show no hydronephrosis. The left paravertebral abdominal mass (*) causes an asymmetric psoas shadow and displaces the ureters to the left. It was identified as an abdominal aortic aneurysm. With kind permission, Dr. G. Antes, Kempten.

Ectopic ureter with left-sided ureteral duplication: the upper pole ureter drained into the prostatic urethra. Massive hydronephrosis of the upper pole system (marked with *; a nephrostomy tube is in place) displaced the lower pole calyces caudally (dropping lily sign on intravenous urography). With kind permission, Dr. N. Dreger and Prof. Dr. S. Roth, Wuppertal.

CT or MR urography:

CT or MR urography can establish the diagnosis and reliably detect associated malformations [fig. CT of ureteral duplication and MR urography of a duplex kidney]. In children and for elective imaging, MR urography is preferred to avoid radiation exposure. CT is useful when a stone or tumor is suspected, symptoms are acute, MRI is unavailable, or MRI is contraindicated.

CT of a left-sided ureteral duplication: visualization of the anatomy with 3D volume rendering (VR). With kind permission, Dr. H. Ruhnke, Radiologie im Zentrum, Augsburg.

Left-sided duplex kidney on MR urography (T2-weighted, MIP): marked ectasia and hypoplasia of the upper pole system. With kind permission, Dr. med. A. Altenburger, Radiologie Augsburg Friedberg ÜBAG, www.radiologie-augsburg.de.

Voiding cystourethrography:

Voiding cystourethrography is indicated for recurrent febrile urinary tract infections, ureterocele, hydroureteronephrosis, or suspected vesicoureteral reflux. A ureterocele may be seen during the early filling phase. In a duplex system, reflux usually involves the lower pole system.

Endoscopy:

Cystoscopy, retrograde pyelography, or ureteroscopy may be performed for unclear findings or before planned endoscopic treatment.

Renal scintigraphy:

Renal scintigraphy can assess the function of the upper and lower renal moieties separately. DMSA is suitable for evaluating renal function and scarring; MAG3 is suitable for evaluating drainage obstruction.

Treatment of the Duplex Kidney

Ureteral duplication is a normal variant and does not require treatment in the absence of associated malformations or symptoms. Treatment is guided by the associated malformations and symptoms, including vesicoureteral reflux, ectopic ureter, ureterocele, recurrent urinary tract infections, nephrolithiasis, urinary incontinence, or urinary obstruction.

References

EAU guidelines: Paediatric Urology

  Deutsche Version: Ureteroduplikatur

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