Neurology India, Vol. 59, No. 3, May-June, 2011, pp. 486-487
Unique radiologic feature of spinal plasmacytoma: Mini-brain appearance
Manish K Kasliwal, John E O«SQ»Toole
Department of Neurosurgery, RUSH University Medical Center, Chicago, IL, USA
Correspondence Address: Manish K Kasliwal Department of Neurosurgery, Suite 1115 RUSH University Medical Center, Chicago, IL 60612 USA email@example.com
Code Number: ni11146
A 50-year-old man with significant past medical history of diabetes and hypertension presented with complaints of low back and right lower extremity pain. He had a history of about 50 pound weight loss the last few months. There was no history suggestive of any bowel or bladder involvement. General examination was within normal limits with no evidence of any focal neurologic deficit on nervous system examination. MRI of the lumbar spine revealed the presence of an L4 vertebral body lesion extending into the pedicles, transverse process, and inferior articular facet on the right side with extension into the soft tissues and psoas muscle. CT scan of the lumbar spine depicted an expansile lytic L4 vertebral body lesion with involvement of thte inferior articular facet and posterior elements on the right side along with some soft tissue component [Figure - 1]. The differential diagnosis included metastatic tumor, plasmacytoma, giant cell tumor, chondrosarcoma, and chordoma so a CT-guided biopsy was performed along with a systemic workup. Serum immunofixation was within normal limits and there was no evidence of any other tumor on systemic imaging. CT-guided biopsy confirmed the diagnosis of plasmacytoma. The patient was managed conservatively in view of his intact neurologic condition and was referred to oncology and radiation oncology for further management. A careful review of axial cuts from lumbar CT and MRI scans demonstrated the presence of a characteristic "mini-brain" appearance [Figure - 2].
Solitary plasmacytoma involving the axial skeleton manifests predominantly as a lytic lesion involving the vertebral body not infrequently involving the posterior elements. Such findings are not specific and may be seen in other tumors involving the spine. Although the pattern of vertebral involvement can give a clue to certain pathologies, a biopsy remains crucial for diagnosis. However, a fairly characteristic mini-brain-like radiologic appearance of plasmacytoma has been described in few cases in the literature as in the present case, and this finding seems to have a very high degree of specificity. ,, Major et al described few cases of plasmacyoma with such an appearance and reported that it may even obviate the need of biopsy before treatment. Increased cortical strut thickness of the residual bone due to stress following destruction of the bone due to tumor has been proposed as a possible reason for this reproducible appearance, best seen on axial images from MRI or CT.  The thickened cortical struts resemble sulci in the brain, leading to the mini-brain appearance [Figure - 2]. The fact this radiologic appearance has not been frequently reported in the literature to date may simply reflect a lack of common appreciation of this finding.
The radiological "mini-brain" appearance of spinal plasmacytoma appears very specific to this disease entity and should be looked for on axial CT and MRI when evaluating primary spinal neoplasms. Although a biopsy may still be needed to confirm the diagnosis, this radiologic sign may direct specific workup geared toward plasmacytoma/myeloma and can expedite the diagnostic evaluation and initiation of treatment.
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