The endless differential diagnosis of acute obstructive renal failure: unusual challenges for the sharp-sighted clinician.

Obstruction of urine outflow can result from mechanical blockade as well as from functional defects. In adults, urinary tract obstruction is due mainly to acquired defects, such as pelvic tumors, calculi, and urethral stricture. In childhood it is mostly due to congenital malformations. In this article we present two rare cases of acute obstructive renal failure that presented with hydronephrosis. These cases underline the wide range of causes that may lead to this clinical feature.