Applied Radiology

Diagnosis

Plasmacytoma

Findings

Axial and sagittal CT images as well as sagittal T1-weighted pre- and postcontrast, T2-weighted, and STIR images are provided. The CT images demonstrate a mildly expansile lytic lesion involving the vertebral body with extension into the left pedicle. There is bulging of the posterior aspect of the vertebral body with preservation of the remaining cortex. Numerous thickened cortical struts are present within the lytic lesion. The magnetic resonance (MR) images demonstrate the lesion is mildly hyperintense to muscle on T1-weighted images, and hyperintense to skeletal muscle on T2-weighted and STIR images. Postcontrast images demonstrate mild homogenous enhancement.

Discussion

Plasmacytomas are solitary monoclonal plasma cell tumors, which may occur within bones or soft tissue. The spine is the most common site of involvement, seen in 34% to 72% of cases, most commonly within the thoracic, lumbar, sacral, and cervical vertebrae in descending order of frequency. Other locations include ribs, long bones, sternum, clavicle, pelvis, and scapula. The mean age of presentation is 55 years with men being affected at twice the incidence of women. Patients most frequently present with pain, often due to pathologic fracture, or spinal cord/nerve root compression syndrome. Lesions in superficial bones may also present with a mass on physical examination, with or without pain.

The diagnostic criteria for a solitary bone plasmacytoma consist of: 1) solitary lesion with biopsy demonstrating plasma cells; 2) absence of other lesions as proven by a negative skeletal survey and MRI of the spine, pelvis, and proximal femurs/humeri; 3) negative clonal cells (plasma cells <5%) in marrow aspirate; 4) no anemia, hypercalcemia, or renal impairment attributable to myeloma; 5) low or absent serum/urine monoclonal proteins; and 6) preserved levels of uninvolved immunoglobulins.

Imaging findings of vertebral body plasmacytomas include a lytic lesion with or without dense vertical striations, or a pathologic compression fracture on plain film. CT imaging findings again include a destructive lesion, which most often includes the posterior elements. A soft tissue component may be present and vertical struts may be better appreciated than on plain film. The vertical struts are presumably secondary to compensatory hypertrophy of the remaining trabecular bone. The presence of thickened vertical struts within an expansile lytic lesion on axial CT/MR images has been termed the “mini brain” appearance. Alternatively, a collapsed vertebral body may also be seen with evidence of a lytic lesion, best appreciated within the uncollapsed posterior elements. On MR images, the lesions are usually iso/hypointense to skeletal muscle on T1-weighted images, iso/hyperintense on T2-weighted images, and hyperintense on STIR images. Post contrast images demonstrate mild to moderate diffuse enhancement.

Solitary bone plasmacytomas typically have an indolent course. Treatment consists of tumor excision with adjuvant radiation. The use of chemotherapy is controversial, but may be used at some centers. Local recurrence is uncommon, but approximately half of patients will eventually develop overt multiple myeloma.

1. Major NM, Helms CA, Richardson WJ. The "mini brain": plasmacytoma in a vertebral body on MR imaging. AJR Am J Roentgenol. 2000;175:261-263.
2. Ooi GC, Chim JC, Au WY, et-al. Radiologic manifestations of primary solitary extramedullary and multiple solitary plasmacytomas. AJR Am J Roentgenol. 2006;186:821-827.