Patient with several year history of lymphoma on and off chemotherapy. Fairly characteristic appearance of renal/perirenal disease with multiple ill defined masses and involvement of the cortex. 

Given moderate hydronephrosis, urology consult would be appropriate. If tissue diagnosis were needed, ultrasound-guided biopsy would be feasible. 

The differential diagnosis for perirenal infiltrative soft tissue involves several unusual diagnoses, and is worth trying to remember: 

• lymphoma
• retroperitoneal fibrosis
• igG4 sclerosing disease
• Erdheim-Chester disease
• extramedullary hematopoiesis
• amyloidosis
• plasmacytoma