Retroperitoneal fibrosis: use of CT in distinguishing among possible causes.

Retroperitoneal fibrosis (RF) often presents with characteristic clinical and urographic findings that suggest the diagnosis. However, malignant adenopathy may mimic this appearance. CT examinations of 10 patients with medial deviation of the ureters suggesting retroperitoneal fibrosis were reviewed. Six had idiopathic RF, two had perianeurysmal fibrosis, and two had malignant retroperitoneal adenopathy. The CT findings in idiopathic RF included a homogeneous mass enveloping the ureters, aorta, and inferior vena cava. The aortic aneurysm was easily seen in both patients with perianeurysmal fibrosis. In one of the two patients with malignant retroperitoneal adenopathy, the CT findings mimicked idiopathic RF. In the other patient, the nodes involved with metastatic melanoma caused significant anterior displacement of the aorta and inferior vena cava. This marked anterior displacement of the great vessels is not seen in idiopathic RF, and may be useful in differentiating these entities.