Duplicated collecting system

Contributors: Cafer Zorkun M.D., PhD.

Overview
Duplicated collecting system is the most common upper urinary tract anomaly, affecting nearly 15% of the population.

Embryologically occurs when 2 separate ureteric buds arise from a single wolffian duct. The future lower pole ureter separates from Wolffian duct earlier and migrates superiorly and laterally as the urogenital sinus grows.

Weigert-Meyer rule for bladder insertion: the upper pole ureter inserts inferior and medial to lower ureter.

Alternatively, the 2 ureters may fuse to form a single ureter prior to inserting into the bladder, termed a bifid system.

The lower pole system is usually dominant, while the upper system may drain a single or few calices.

The upper pole ureter may demonstrate a ureterocele, which is associated with ureteral obstruction and recurrent UTIs in children. The upper pole ureter may also be ectopic or stenotic.

Symptoms

 * Most patients are symptomatic and are diagnosed as an incidental finding.
 * Vesicoureteral reflux
 * Recurrent UTIs, with resultant parenchymal scarring
 * Ureteropelvic junction obstruction
 * Hydronephrosis, which may be severe enough to cause a palpable mass and hypertension
 * Urinary incontinence with ectopic insertion in female

Diagnostic Findings

 * Excretory urography may demonstrate the duplicated anatomy. Limitation is that a poorly functioning system may not excrete contrast and may resemble a mass.
 * The drooping lily sign: inferolateral displacement of the opacified lower pole moiety in a duplex kidney from an obstructed (unopacified) upper pole moeity.
 * Voiding cystourethrogram is usually diagnostic and may demonstrate ectopic insertion and reflux.
 * Ultrasound is an easy, noninvasive exam that may show the duplex kidney and hydronephrosis. May not be able to differentiate between complete duplication and a bifid system.
 * CT urography may demonstrate the duplicated system and show the location of bladder insertion for each moiety.
 * MR urography may demonstrate the typical anatomic findings, but is an expensive alternative.
 * Renal scintigraphy can show the anatomy as well as evaluate for renal function.

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