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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.
Inverted Y ureteral duplication:
Two separate ureteral buds merge on the way to the metanephric blastema, resulting in a common renal unit. Very rare.
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.
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.
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.
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).
A duplex kidney is often an incidental finding during the diagnostic workup for other diseases [fig. duplex kidney in IVU]. If the upper pole system has only poor kidney function, imaging with urography may miss the upper portion of the duplex kidney. A non-contrasting upper portion should be suspected if the number of calyces is reduced or by a larger distance between the renal system to the spine. Sometimes, a ureterocele is delineated in the bladder.
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.
Cystoscopy, retrograde pyelography, and possibly ureteroscopy depending on complaints and other findings.
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).
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