This case begins with an unusual (but highly characteristic) appearance of symmetric perinephric and perihilar stranding - the "hairy kidney" sign. It is appropriate to confirm the suspicion of Erdheim-Chester disease with long bone radiographic which looks for the characteristic medullary sclerotic lesions, and finally with a bone scan confirming increased uptake in this same pattern. ECD is a non-Langerhans histiocytosis with multisystem involvement, but most commonly presents with findings surrounding the kidneys and involvement of the long bones. 

Case courtesy of Dr. Barry Rush