[Case of pelvic retroperitoneal fibrosis].

A 66-year-old man visited his nearby clinic with a complaint of left lower abdominal pain. Abdominal CT scan showed left hydronephrosis due to lower ureteral involvement by infiltrative retroperitoneal mass located outside of the left posterior wall of the bladder and left seminal vesicle. He was referred to our hospital for further examination. Pathological diagnosis of the percutaneous CT-guided biopsy of retroperitoneal mass was fibrosis without any malignant tumor. Because we could not rule out the possibility of the secondary fibrosis accompanied by malignant tumor, we performed surgical resection of the retroperitoneal mass involving left ureter and confirmed that the mass contains no malignant tumor by frozen section analysis. We augmented the defected ureter by Boari flap method. We should be noticed that retroperitoneal fibrosis could be a differential diagnosis of retroperitoneal pelvic mass.