[A case of idiopathic retroperitoneal fibrosis with renal subcapsular urinoma resolved by steroid therapy].

A case of idiopathic retroperitoneal fibrosis is reported. The patient was a 63-year-old man with the complaint of right flank pain, general fatigue and weight loss. Intravenous pyelography revealed right hydronephrosis and peripelvic extravasation. Abdominal computed tomography showed subcapsular urinoma of the right kidney and mass lesion surrounding the aortic bifurcation. Retrograde pyelography demonstrated a narrow segment at the middle portion of the right ureter through which the ureteral catheter could be easily passed. Magnetic resonance imaging showed a low-intensity mass on T1 weighted images and a heterogeneous mass on T2 weighted images. Steroid therapy was selected under the diagnosis of idiopathic retroperitoneal fibrosis with subcapsular urinoma of the right kidney. Prednisolone was administered for 60 days, resulting in the complete disappearance of the urinoma.