Extraosseous multiple myeloma: imaging spectrum in the abdomen and pelvis.

Multiple myeloma represents a subset of plasma cell dyscrasias characterized by the proliferation of plasma cells typically in the bone marrow, representing approximately 1% of all cancers and 15% of hematologic malignancies. Often multiple myeloma is limited to the skeletal system; however, a small percentage (<5%) of patients will develop extraosseous manifestations. We review the current WHO classification of plasma cell dyscrasias and use multimodality imaging including US, CT, MRI, and PET-CT to illustrate the spectrum of extraosseous multiple myeloma in the abdomen and pelvis. Because extraosseous multiple myeloma is associated with a poorer prognosis and decreased survival, it is important for the radiologist to become familiar with a variety of extraosseous manifestations in the abdomen and pelvis, especially in a patient with a known diagnosis of multiple myeloma and the development of an abdominal or pelvic mass.