Plasma cell myeloma (multiple myeloma) and solitary plasmacytoma are clonal neoplastic proliferation of plasma cells of bone marrow derivation. Plasma cell myeloma is a multicentric disease with systemic manifestations, whereas solitary plasmacytoma is a unicentric disease, localized to a single bone. Multiple solitary plasmacytomas without evidence of multiple myeloma may occur.

Plasma cell myeloma is the most common malignant primary bone tumor. It commonly occurs in patients in their sixth and seventh decades of life, and is rare under the age of 40 years. Solitary plasmacytomas tend to occur at a younger age, with a median age of 55 years at diagnosis. Plasma cell myeloma affect both genders equally, whereas solitary plasmacytomas are more common in males than in females (M:F = 2:1).

Plasma cell myelomas and solitary plasmacytomas are found in bones containing hematopoietic marrow, usually the axial skeleton. Solitary plasmacytomas have been reported most commonly in the vertebra, and other possible sites include ribs, skull, pelvis, and femur.

Plasma cell myelomas may have various appearances according to the site of involvement and type of lesion. Typical plasma cell myelomas present with multiple well-demarcated osteolytic lesions with medullary location, often referred to as “punched-out” lesions (Fig. 6.1). In bones with small calibers, such as the rib, plasma cell myelomas may cause expansion of the bone (Figs. 6.2, 6.3, and 6.4). However, periosteal reactions are rare. Atypical cases may present with more aggressive features with either moth-eaten or permeative pattern of bone destruction (Fig. 6.5). Diffuse osteopenia in the spine with or without compression fractures may be the sole finding, making the diagnosis of myeloma difficult. Occasionally, myeloma may present with multiple sclerotic lesions, usually in the setting of POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, skin changes) (Fig. 6.6).

Plasma cell myeloma and solitary plasmacytoma show nonspecific findings on MR imaging. MR may be useful in (i) detecting small lesions not readily seen on radiographs and (ii) evaluating the presence and extent of soft tissue extension.

Lymphoma is a disease histologically characterized by the proliferation of lymphocytes, histiocytes, and their precursors. Lymphoma of bone can be classified as primary lymphoma of bone or secondary bone lymphoma. Secondary bone lymphoma refers to the involvement of bone secondary to a systemic disease with nodal or other extranodal involvement, and is not uncommon. On the other hand, primary lymphoma of bone is defined as lymphoma confined to the bone or bone marrow without evidence of concurrent systemic disease, and is rare. The majority of primary bone lymphomas are non-Hodgkin lymphomas.

Primary lymphoma of bone accounts for <5 % of primary bone tumors. It may occur in any age group, but has a peak prevalence in the sixth and seventh decades of life. It is slightly more common in males(male: female = 1.5:1).

The femur is the most commonly affected site, accounting for 25 % of the cases. Within the femur, the lesion is usually located in the metadiaphysis. The spine and pelvic bone, humerus, tibia, and head and neck are the other possible sites.