Presentation
Low back pain.
Patient Data
Increased lucency of the left sacral ala.
Lumbar scoliosis to the right with mild degenerative change.
Lytic lesion of the left sacral ala with cortical thinning/dehiscence extending to the left sacro-iliac joint and the left S1 and S2 neural exit foramina abutting and surrounding the nerve roots. Minimal extension into the sacral canal. Small volume soft tissue density in the presacral space.
Core biopsy performed with CT fluoroscopy using a co-axial technique.
Histopathology
MACROSCOPIC:
Sacral core biopsy –in block A, – 1 core 19 mm in length and a 2 mm fragment, in block B – 1 core 16 mm in length and a 3 mm fragment. All processed.
MICROSCOPIC:
Sections from the variably hemorrhagic cores are dominated by a relatively uniform population of plasmacytoid cells. These cells show eccentric nuclei, slightly enlarged relative to small mature lymphocytes, with an eccentric cytoplasm which in some cells contains eosinophilic bodies known as Russell Bodies. Careful search shows some nuclear variation within this population. There is no polylobation of nuclei evident and no evidence of necrosis. No bone has been included. There is a small fragment of uninvolved fibrous connective tissue. Immunohistochemically the population shows uniform staining with plasma cell markers CD138 and MUM1. The kappa/lambda staining shows a vast predominance of kappa in the population. SOX10 is negative.
DIAGNOSIS:
Core biopsies from sacral mass confirming a neoplastic plasma cell proliferation diagnostic of either a solitary plasmacytoma in the absence of no other lesions or one lesion in involved multiple myeloma.
Case Discussion
Follow-up imaging demonstrate no other lytic deposit. The sacral ala is a common blind spot for bone lesions and should be reviewed carefully on x-rays.
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