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Duplicated Ureter or Duplex Kidney: Symptoms and Diagnosis

Definition of Duplex Kidney and Ureteral Duplication

The duplex kidney is an anatomic variant of the ureter and pyelocalyceal system with a large variability [variants of the duplex kidney]:

Complete ureteral duplication:

Duplex kidney with complete duplicated ureters, renal pelvis and two orifices of the ureters.

Ureter fissus or bifid ureter:

Duplex kidney with incomplete ureteral duplication and a common orifice of the ureter.

Bifid renal pelvis:

Duplex kidney with duplication of the renal pelvis and a common ureter.

Different variants of the duplex kidney: duplicated ureter (left), ureter fissus (center) and bifid renal pelvis (right).

Inverted Y ureteral duplication:

Two separate ureteral buds merge on the way to the metanephric blastema, resulting in a common renal unit. Very rare.

Ureteral triplication:

Three independent ureteral orifices with three complete ureters or incomplete ureteral triplication with two orifices of the ureters (see ureter fissus).

Epidemiology of the Duplex Kidney

Prevalence 1:150 (0.7%)

Etiology of the Duplex Kidney

Two ureteric buds:

Two ureteric buds on the mesonephric duct (Wolffian duct) result in two separate ureters and a duplex kidney in a common renal capsula. The ureteric buds rotate by 180 degrees while being incorporated into the urogenital sinus: the latero-cranial orifice drains the lower pole of the kidney, and the medio-caudal orifice drains the upper pole of the kidney. This relation is called Weigert-Meyer 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 to a normal kidney with 8–9 calyces, the duplex kidney consists of 11–12 calyces. The upper pole system is smaller, with an average of 3–4 calyces.

Associated malformations:

Vesicoureteral reflux to the lower pole system (40%), ureteropelvic junction obstruction of the lower pole system, ectopic ureteral orifice of the upper pole system (with or without obstruction), ureterocele of the upper pole ureter, hypoplastic and dysplastic renal parenchyma most common of the upper pole system.

Pathophysiology:

Duplication of the ureter is associated with vesicoureteral reflux or hydronephrosis, leading to a susceptibility to urinary tract infections or nephrolithiasis.

Signs and Symptoms of a Duplex Kidney

Associated malformations may lead to urinary tract infections, nephrolithiasis, fever, or abdominal tumor. Without malformations, a duplex kidney usually presents without symptoms.

Diagnostic Workup

Sonography:

Without associated malformations, a normal finding in renal ultrasound is seen. A duplex kidney may be recognized if renal parenchyma separates two renal pelves (fig. US duplex kidney). It is easier to detect a duplex kidney with ureteroceles or hydronephrosis; most often, the upper pole system is 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:

A duplex kidney is often an incidental finding during the diagnostic workup for other diseases [fig. duplex kidney in IVU]. Due to poor renal function, urography often lacks to contrast the upper part of the duplex kidney. Hints for a non-contrasting upper portion are obtained from the small number of calyces shown, inferior-lateral displacement of the lower pole (dropping lily sign) and the greater distance of the renal system to the spine. Sometimes, a ureterocele is delineated in the bladder.

Left-sided duplex kidney in intravenous urography: both parts of the left-sided duplex kidney present without hydronephrosis. The urinary tract did not cause the complaints of the patient. Note the abdominal mass due to an abdominal aortic aneurysm, which displaces the left psoas shadow. With kind permission, Dr. G. Antes, Kempten.

Ureterectopy with a left-sided ureteral duplication: the ureter of the upper pole system led into the prostatic urethra. The massive hydronephrosis of the upper pole system (indicated with (*) and an inserted kidney fistula) led to a caudal displacement of the lower pole calyces (dropping lily sign in intravenous urography). With kind permission, Dr. N. Dreger und Prof. Dr. S. Roth, Wuppertal.

Computed tomography:

The diagnosis and accompanying malformations are reliably detected with CT, which is increasingly replacing IVP in diagnostics [fig. Ureteral duplication in CT].

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.

Voiding cystourethrogram:

Voiding cystourethrogram is indicated for recurrent urinary tract infections or dilatation of the pyelocalyceal system. A possible ureterocele is detectable in the early filling phase.

Endoscopy:

Cystoscopy, retrograde pyelography, and possibly ureteroscopy depending on complaints and other findings.

Renal scintigraphy:

Renal scintigraphy enables the separate determination of the renal function of the upper and lower part of the duplex kidney for further treatment planning.

Treatment of the Duplex Kidney

Duplex kidney or ureteral duplication is a normal variant and, thus, not subject to treatment. The accompanying malformations and symptoms guide the therapy (vesicoureteral reflux, ureterocele, ectopic ureter, recurrent urinary tract infections, nephrolithiasis, or urinary tract obstruction).

References

EAU guidelines: Paediatric Urology

  Deutsche Version: Ureteroduplikatur