B-Cell Lymphoma, Retroperitoneal

56-year-old male with history of chronic abdominal and low back pain. These images demonstrate a solid appearing, T1 isointense, T2 mildly hyperintense, mildly enhancing lesion with few enhancing vessels. The lesion demonstrates lobulations and prominent diffusion restriction. It abuts and partially encases the abdominal aorta just inferior to the origin of the left renal artery without definite invasion. The lesion also partially effaces the prevertebral fat anteriorly on the left. The differential for the mass includes retroperitoneal sarcoma as well as lymphoma given the prominent diffusion extraction. Malignant B-cell lymphoma was found on biopsy. The majority of non-Hodgkins lymphoma the B-cell type. Risk factors include previous viral infection such as Epstein-Barr virus, HIV, and HSV as well as bacterial infection, chronic immunosuppression, and prior chemotherapy.