Hydronephrosis and hydroureter are common clinical conditions encountered not only by urologists but also by emergency medicine specialists and primary care physicians. Hydronephrosis is defined as distention of the renal calyces and pelvis with urine as a result of obstruction of the outflow of urine distal to the renal pelvis. Analogously, hydroureter is defined as a dilation of the ureter.

The presence of hydronephrosis or hydroureter can be physiologic or pathologic. It may be acute or chronic, unilateral or bilateral. It can be secondary to obstruction of the urinary tract, but it can also be present even without obstruction.

Obstructive uropathy refers to the functional or anatomic obstruction of urinary flow at any level of the urinary tract. Obstructive nephropathy is present when the obstruction causes functional or anatomic renal damage. Thus, the terms hydronephrosis and obstruction should not be used interchangeably.

The etiology and presentation of hydronephrosis and/or hydroureter in adults differ from that in neonates and children. Anatomic abnormalities (including urethral valves or stricture, and stenosis at the ureterovesical or ureteropelvic junction) account for the majority of cases in children. In comparison, calculi are most common in young adults, while prostatic hypertrophy or carcinoma, retroperitoneal or pelvic neoplasms, and calculi are the primary causes in older patients.

Hydronephrosis or hydroureter is a normal finding in pregnant women. The renal pelvises and caliceal systems may be dilated as a result of progesterone effects and mechanical compression of the ureters at the pelvic brim. Dilatation of the ureters and renal pelvis is more prominent on the right side than the left side and is seen in up to 80% of pregnant women. These changes can be visualized on ultrasound examination by the second trimester, and they may not resolve until 6-12 weeks post partum.