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- 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.

- 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

Imaging 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.

Images courtesy of our radiology website partner, radsWiki (http://www.radswiki.net)

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Comment by radRounds Radiology Network on December 26, 2008 at 1:28pm
MRU very expensive. Usually we do VCUG. MRU is performed mostly in adults and in tertiary care centers where resources are abundant or referring physician prefers it/looking for additional anatomic resolution/characterization. MRU has pretty pictures but may not be always needed.
Comment by saeed rad on December 26, 2008 at 1:23pm
Is the MRU expensive in America too? Here it is so, and most of the people prefer ordinary urography or VCUG. Thanx for the educational embriologic explanation.

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