Ureteropelvic junction obstruction in children.

Infants with ureteropelvic junction obstruction usually present with an abdominal mass or a urinary tract infection, which generally leads to prompt diagnosis. In children over age six, the diagnosis is often delayed because they frequently present with poorly localized abdominal pain simulating functional or gastrointestinal illness. Children with unexplained abdominal pain should undergo urologic evaluation, even if urinalysis and urine culture are negative. Ultrasonography is useful for detecting hydronephrosis.