Solution: This is a difficult case. Retroperitoneal fibrosis is an uncommon process that typically results in encasement of the aorta, IVC and possibly ureters with inflammatory cells, fibroblasts and collagen. The majority of cases are idiopathic and it is sometimes called Ormond disease. It can also be associated with medications, infections (e.g. TB and syphilis), CTD, and radiation therapy. Since malignancies such as lymphoma can also elicit a desmoplastic reaction, biopsy, preferably at multiple locations with core needle is needed to make the diagnosis (i.e. it is a diagnosis of exclusion). Findings are non-specific and can include subtle retroperitoneal soft tissue stranding all the way to an infiltrative large mass, as in this case. A discriminatory finding can be that with benign RP fibrosis, the aorta is usually not lifted off the spine. If it is, then favor malignant causes such as lymphoma or metastases, particularly from testicular cancer. It usually responds to steroid therapy.