Ultrasound follow-up of an unusual giant urinoma in a newborn.

Urinoma, defined as an encapsulation of urine caused by urine extravasation into the perirenal space either through rupture of a calyceal fornix or a tear in the renal parenchyma, is an uncommon finding in prenatal diagnosis and the neonatal period. Urinoma can be associated with any urinary tract obstruction, or, as reported in several published cases, related to vesicoureteral reflux, kidney dysplasia, or complication arising during amniocentesis. We report on a newborn with a perinatal urinoma, with initial slight corpusculated fluid associated with nonobstructive and nonrefluxing megaureter, and no signs of kidney dysplasia. Close sonography follow-up of the urinoma allowed complex differential diagnoses, including cystic, septated, and solid perirenal masses, due to dissimilar and peculiar ultrasound images during urinoma evolution stages.