Clinical History
55-years-old male patient presented with quadriparesis and neck pain after trivial trauma.
Imaging Findings
MRI cervical spine revealed altered signal intensity lesion involving vertebral body, right articular process, right transverse process, right pedicle of C5 and C6 vertebra, right lamina of C6 vertebra and right-sided facet joint between C5 and C6 vertebrae.
The lesion appeared hyperintense on T2/STIR sequences and hypointense on T1 sequence. The lesion showed intense homogeneous enhancement on post-contrast study.
The lesion extended into the right-sided prevertebral and paravertebral region at C5 and C6 vertebral level. The lesion was encasing the right vertebral artery, extending into the epidural region on the right side and causing compression and left side displacement of the cervical spinal cord at C5 and C6 vertebral level.
There were thick cortical struts in the C6 vertebral body predominantly on the left side. These struts were hypointense on T2/T1 images and the surrounding lesion hyperintense on T2 images. These struts resembled sulci of brain and the lesion looked like gyri of brain, showing a "Mini brain” sign in the axial images.
Discussion
A plasmacytoma is a discrete, solitary mass of neoplastic monoclonal plasma cells in either bone or soft tissue (extramedullary). It can be considered as a singular counterpart of multiple myeloma. [1]
Solitary plasmacytomas can be divided into two groups according to location: plasmacytoma of the skeletal system / solitary bone plasmacytoma and extramedullary plasmacytoma. [2]
A solitary bone plasmacytoma may involve any bone, but it has a predisposition for the red marrow-containing axial skeleton, mainly spine, rib, sternum, clavicle, skull or scapula. [2, 3]
Diagnostic criteria for solitary bone plasmacytoma are: single area of destruction due to clonal plasma cells, bone marrow plasma cell infiltration <5% of all nucleated cells, absence of osteolytic bone lesions or other tissue involvement, absence of anaemia, hypercalcaemia or renal impairment, low or absent serum / urine monoclonal protein, preserved levels of uninvolved immunoglobulins. [4]
X-ray and CT show expansile lytic lesions. MRI shows expansile soft tissue intensity lesions, which appear hyperintense on T2 / STIR and hypointense on T1 images. On post-contrast study, plasmacytoma shows variable moderate to intense enhancement. [3]
In solitary vertebral body plasmacytoma, thick cortical struts form in the vertebral body. The characteristic appearance of thickened cortical struts is probably a result of a stress phenomenon from the lytic process of the plasmacytoma forcing the remainder of the bone to increase thickness as a compensatory response to weakening bone. Perhaps an explanation of this appearance, which is not seen in other primary bone or metastatic spine lesions, concerns the less aggressive nature of plasmacytoma compared with other tumours that destroy bone. The cortical thickening in the arrangement of plasmacytoma appears to be unique in this tumour. This appearance can also be seen on CT of plasmacytoma. [3]
In our case, biopsy was performed and plasmacytoma could be confirmed.
Teaching point: A “mini brain” appearance in an expansile lesion of the vertebral body is pathognomonic of solitary plasmacytoma. It is important to appreciate this finding because it may help radiologists recommend appropriate laboratory studies and facilitate early and appropriate treatment. For the patient, an early diagnosis on MR imaging may obviate biopsy. [3]
Differential Diagnosis List
Solitary plasmacytoma involving C5 and C6 vertebrae with "Mini brain"appearance
Metastasis
Giant cell tumour
Aneurysmal bone cyst
Final Diagnosis
Solitary plasmacytoma involving C5 and C6 vertebrae with "Mini brain"appearance
