Retroperitoneal fibrosis.

Retroperitoneal fibrosis is a rare syndrome hallmarked by a fibrosclerotic tissue in the retroperitoneum, often leading to encasement of the ureters. About two-thirds of cases of retroperitoneal fibrosis are idiopathic, while the remaining cases are secondary to a variety of different causes, including drugs, tumors and infections. Idiopathic retroperitoneal fibrosis may be associated with abdominal aorta aneurysms, with vasculitis of the thoracic aorta and of epi-aortic vessels, or both. Most patients present with abdominal and/or low back pain. Serum markers of inflammation are usually, but not invariably, elevated. The diagnosis is secured by computed tomography or magnetic resonance imaging, which typically show an enhancing retroperitoneal mass medially dislodging the ureters. Positron emission tomography can be useful to document the extent and metabolic activity of the inflammatory process. Treatment rests on glucocorticoids with a tapering scheme variably combined with immunosuppressive agents. In cases of ureter obstruction, relief of obstruction by stenting or ureterolysis is required.