Ormond's disease or secondary retroperitoneal fibrosis? An overview of retroperitoneal fibrosis.

Retroperitoneal fibrosis represents a rare inflammatory disease. About two thirds of all cases seem to be idiopathic (= Ormond's disease). The remaining one third is secondary and may be ascribed to infections, trauma, radiation therapy, malignant diseases, and the use of certain drugs. Up to 15 % of patients have additional fibrotic processes outside the retroperitoneum. The clinical symptoms of retroperitoneal fibrosis are non-specific. In sonography retroperitoneal fibrosis appears as a retroperitoneal hypoechoic mass which can involve the ureters and thus cause hydronephrosis. Intravenous urography and MR urography can demonstrate the typical triad of medial deviation and extrinsic compression of the ureters and hydronephrosis. CT and MRI are the modalities of choice for the diagnosis and follow-up of this disease. The lesion typically begins at the level of the fourth or fifth lumbar vertebra and appears as a plaque, encasing the aorta and the inferior vena cava and often enveloping and medially displacing the ureters. In unenhanced CT, retroperitoneal fibrosis appears as a mass that is isodense with muscle. When using MRI, the mass is hypointense in T 1-weighted images and of variable intensity in T 2-weighted images according to its stage: it may be hyperintense in early stages, while the tissue may have a low signal in late stages. After the administration of contrast media, enhancement is greatest in the early inflammatory phase and minimal in the late fibrotic phase. Dynamic gadolinium enhancement can be useful for assessing disease activity, monitoring response to treatment, and detecting relapse. To differentiate retroperitoneal masses, diffusion-weighted MRI may provide useful information.