Ureteropelvic junction obstruction in infants mimicking ureterovesical junction obstruction on sonography.

We present two infants with ureteropelvic junction obstruction with very large renal pelves, which extended to the level of the urinary bladder. In both cases, the distal aspect of the renal pelvis simulated a dilated distal ureter, leading to the incorrect sonographic diagnosis of ureterovesical junction obstruction. Awareness of this potential pitfall on sonography is important when imaging infants with prenatal diagnosis of hydronephrosis.