DUPLEX COLLECTING SYSTEM

Double collecting system is a developmental anomaly in which single renal parenchyma is drained by two pelvicalyceal system and bifid ureters (partial duplication) or two ureters (complete duplication). It occurs when the single ureteric bud bifurcates before bifurcation of the ampulla. Complete ureteric duplication ensues when two ureteric buds arise from Wollfian ducts. Patients are usually symptomatic. However, may present due to reflux, infection, obstruction or urinary incontinence. In case of partial duplication of ureters, the two ureters may join at pelviureteric junction or before draining into the urinary bladder. In complete duplex collecting syste, there are two separate ureteric openings. According to the Weigert-Meyer rule, the lower pole ureter inserts normally and the upper pole ureter is  ectopic and  inserts  inferomedial to the lower ureteric insertion. Imaging features on excretory urography includes: i. relatively large kidney ii. asymmetric calyces or reduction in number of calyces iii. Drooping Lily Sign: due to inferolateral displacement of the lower pole calyceal system due to obstructed non opacified upper pole segment. iv. Nubbin Sign: non opacification of lower pole collecting system appears as lower pole mass or renal infarct.