Perinephric Extramedullary Disease in Multiple Myeloma.

Extramedullary disease represents an aggressive form of multiple myeloma occurring outside the skeleton and is a poor prognostic indicator. Extramedullary disease most commonly involves the skin, muscle, pleura, lymph nodes, liver, and central nervous system. Infrequently, extramedullary disease can involve the kidneys or perirenal space. We present 3 cases of perirenal involvement of extramedullary disease on 18 F-FDG PET/CT confirmed with tissue sampling as plasma cell infiltration. Within the limitation of physiologic activity in the kidneys due to 18 F-FDG excretion, close consideration is essential when evaluating multiple myeloma patients for genitourinary involvement as it can resemble other malignancies, hemorrhage, or renal injury.