Congenital giant hydroureteric cistern in a duplex system of an infant.

Duplex collecting system is a congenital genitourinary anomaly commonly found incidentally. Our experience with a duplex system associated with giant hydroureter presenting as mobile abdominal swelling that was noticed from birth, constipation, and failure to thrive is described. Ultrasound and IVU did not assist in making the diagnosis, while a barium enema suggested a colonic duplication. Congenital giant hydroureter should be considered as a differential diagnosis in infants with cystic abdominal swelling. A preserved renal moiety attributed to a dilated ureteric cistern was a unique theory in this case.