Although all patients have hydronephrosis, the degree of renal dysplasia is variable and has important prognostic implications. Those with the most severe renal dysplasia develop the Potter sequence (Plate 2-8) and typically succumb to severe respiratory distress shortly after birth. Those with moderate dysplasia often develop end-stage renal disease (ESRD) during childhood. Finally, those with minimal or no dysplasia often maintain normal or near-normal renal function. To assess for renal abnormalities, an ultrasound should be performed in the neonatal period, and serial measurements of the serum creatinine concentration should be obtained (recognizing that early values reflect maternal, rather than neonatal, renal function). If there is evidence of renal dysfunction, a renal scan can provide more detailed functional information.

The ureters appear broad and tortuous, especially as they approach the bladder, and peristalsis is weak and ineffective. These anomalies reflect a relative lack of smooth muscle cells in the ureteral walls, which instead consist primarily of fibrous connective tissue. In addition, the ureteric orifices are often at abnormally lateral positions, which predisposes them to reflux.