Fig. (1) A 79-year-old male patient was incidentally found to have a large retroperitoneal mass on renal ultrasonography. Contrast enhanced magnetic resonance T1 axial image with fat suppression, showed a large hypovascular left retroperitoneal mass (arrows) predominantly involving the perinephric space and displacing the left kidney. The mass encases the left renal artery (arrowhead) and aorta, without causing any occlusion. These features strongly favor the diagnosis of lymphoma over renal cell carcinoma, which is usually hypervascular that displaces or invades the vasculature. A biopsy of the mass revealed it to be marginal zone lymphoma. The left kidney shows slightly decreased perfusion and mild hydronephrosis as compared to the normal right kidney.