Childhood retroperitoneal fibrosis.

Retroperitoneal fibrosis is rarely considered in the differential diagnosis of ureteral obstruction in children even when clinical presentation and radiologic findings are typical. In a 12-year-old boy admitted with a 2-week history of flank pain computed tomography showed an enhancing mass obstructing the left ureter. Pathologic examination of the mass and adjacent segment of ureter revealed retroperitoneal fibrosis.