The upper-pole collecting system tends to serve about one third of the renal parenchyma. The upper pole ureter generally has a long course within the bladder wall, frequently has an ectopic site of termination, and is also prone to ureterocele. Because of these factors, upper pole obstruction and hydroureteronephrosis is common.

Meanwhile, the lower pole ureter tends to have a short course within the bladder wall because of its superior and lateral site of termination. As a result, it is prone to vesicoureteral reflux (VUR, see Plate 2-21), which can cause lower pole hydronephrosis if severe.

Complete ureteral duplication may be detected using various imaging techniques, including intravenous pyelography, ultrasound, CT, and renal scanning. A classic finding is known as the “drooping lily” sign. It consists of downward and lateral rotation of the lower pole segment by an obstructed, hydronephrotic, poorly functioning (and thus nonopacified) upper pole segment. If the lower pole reflux is marked enough, the drooping lily sign may be seen on voiding cystourethrogram (VCUG).