[Retroperitoneal fibrosis: report of two cases].

In case 1, a 24-year-old man was admitted with left lumbago. Abdominal computed tomographic (CT) scan showed the huge mass (8 x 10 x 13 cm in diameter) in the left retroperitoneal space, which lack enhancement and had a irregular margin. Percutaneous needle biopsy guided by ultrasonography was performed. In case 2, a 74-year-old woman was admitted with right lower abdominal pain. Laboratory data showed the renal failure. Imaging study revealed bilateral hydronephroses and bilateral masses at both common iliac vessels. A retroperitoneoscopic biopsy was performed. We diagnosed both cases as retroperitoneal fibrosis and administered prednisolone for 10 months. The masses decreased in size and the symptoms disappeared in both cases.