All of the disease processes listed are associated with RPF. However, the typical appearance of RPF on CT imaging should not include the finding of para-aortic lymphadenopathy. Malignancy (primary or metastatic) must be excluded as the etiology of the retroperitoneal mass prior to assigning the diagnosis of RPF. Malignancy can account for ureteral obstruction in approximately 10% of cases.3 Lymphoma is the most common primary neoplasm in the differential diagnosis, with carcinoid, multiple myeloma, and sarcoma less commonly identified. Metastatic lesions from pancreatic, prostatic, rectal, colon, breast, and gastric cancer can also involve the retroperitoneum. Malignancy can usually be identified by the appearance or association of retroperitoneal lymphadenopathy, but occasionally it will appear as a flat infiltrating mass, similar to RPF.
3. Usher SM, Brendler H, Ciavarra VA. Retroperitoneal fi-
brosis secondary to metastatic neoplasm. Urology 1977;9:
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