Plasmacytoma

Case contributed by Dr Henry Knipe

Presentation

Long-standing low back pain. No history of recent trauma.

Patient Data

Age: 65 years
Gender: Male

Destructive and expansile lytic lesion of the right ilium and right sacral ala. L4/5 and L5/S1 degenerative change. 

Lytic destructive lesion of the right iliac wing extending to the sacroiliac joint and the right sacral ala. Associated soft tissue mass. 

Dynamic flow and blood pool images of the pelvis show markedly increased blood flow and blood pool activity in the right iliac region and in soft tissue superior to the right iliac bone.

Whole body delayed images show a right of increased uptake in the the right iliac bone with central photopaenia.

Uptake in the left mid lateral cervical spine is most consistent with degenerative disease. Minor degenerative changes are seen in the shoulders and knees.

Lytic soft tissue density expansile lesion of the superior iliac wing, adjacent to the sacro-iliac joint. It contains foci of calcification. It partly destroys the right L3-L5 transverse processes.

The patient proceeded to CT guided biopsy. 

HISTOPATHOLOGY​

MICROSCOPIC DESCRIPTION: Sections show biopsies of loose fibromyxoid/fibrocollagenous stroma, adipose tissue and fragments of bone infiltrated by sheets of atypical plasmacytoid cells which contain mildly pleomorphic nuclei surrounded by small amount of eccentric cytoplasm. Mitotic activity is identified. The tumor cells show diffuse and strong positivity to CD138. Lambda LC is positive. Kappa LC is negative.

DIAGNOSIS: Plasmacytoma.

Case Discussion

A plasmacytoma is a solitary mass of neoplastic monoclonal plasma cells in either bone or soft tissue (i.e. extramedullary). The main (and common) differential diagnoses for this is a solitary metastasis or lymphoma, both of which are difficult to delineate from plasmacytoma/myeloma on imaging. 

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