Duplicated collecting system

Duplication of the renal collecting system is recognized in approximately 1:4000 pregnancies and is more frequent in females. It disproportionately affects the left kidney, and is bilateral in 15% to 20% of cases. Ultrasound (US) may show dilatation of one or both renal pelves, with an intervening band of renal tissue. Ureteral dilatation may be evident, and there may be a ureterocele visible in the bladder. The Weigert-Meyer rule describes the relationship of the ureters. The upper pole ureter inserts medially and inferiorly to the lower pole ureter, with obstruction of the upper pole moiety secondary to a ureterocele. The lower pole ureter inserts laterally in the bladder trigone and has a shortened intravesical segment that leads to reflux. When a diagnosis of a duplicated collecting system is made prenatally, neonatal evaluation is important, as these individuals are prone to reflux, obstruction, and urinary tract infection.