Plasma cells - primary source of immunoglobulins, found in LN, GI submucosa, and bone marrow. A plasmacytoma is a localized lesion, usually of bone composed of monoclonal plasma cells. Most cases +> multiple myeloma, and solitary presenting masses require careful evaluation to exclude other lesions. Some cases of "plasmacytoma" that do not progress to multple myeloma (MM) may be "plasma cell granuloma". Two criteria (Griffiths) for plasmacytoma: survival >12 yrs w/o dissemination and negative bone marrow at autopsy. Conversion to MM usu by 5yrs, rarely >20. Solitary lesions usu spine, pelvis, or extraskeletal (nasal, sinuses, upper airway).
XR - multicystic, expansile w/thickened trabeculae (e.g. AFIP 2468693); pure lytic w/o expansion; pure sclerotic (ivory vertebrae). In spine, may cross intervertebral disc, and simulate infection. Plasmacytoma at any juxtaarticular site may cross joint.
(from RESNICK)