Journal of the Louisiana State Medical Society
dex in the atypical plasma cells with proliferation indices ranging from 10% to 70%, depending on the area examined. Additionally in our case, plasma cells are negative for CD3, CD20, Lambda light chain, and cyclin D1. 9 DIFFERENTIAL DIAGNOSIS AND IMAGING Plasmacytoma may be similar to a meningioma, metas- tasis, sarcoma, chordoma, hemangiopericytoma, and giant cell tumor. Meningiomas can cause a similar high density peripheral lesion with homogeneous enhancement, and they exhibit adjacent dural reaction, so-called “dural tail.” A rare form of intraosseous meningioma can cause lytic bony changes with their blood supply, usually from the middle meningeal artery, while the blood supply of a plasmacy- toma could be from the external carotid artery, mainly from superficial temporal branch and muscular branches of the vertebral artery. 7-10 In multiple myeloma, plasmacytomas are purely lytic and have a clear margin with a narrow zone of transition to normal surrounding bone. The sharp borders, lack of bony sclerosis, and the paucity of periosteal reaction are characteristic findings. 5 On the other hand, plasmacytomas often present as solitary intra- and extra-cranial masses that bridge the diploic site of origin. 3 Solitary plasmacytomas are often large and well-advanced at the time of diagnosis. This is usually due to the fact that the mass is asymptomatic and the patient seeks no immediate care until the mass is sizeable, as in our case. Diagnostic imaging with CT and in particular, MR, is highly sensitive to delineate the lesion and its extension. On CT, the mass appears as an extra-axial lesion of high- attenuation with homogeneous contrast enhancement. 11 On MR, the mass is consistent with a focal lesion involving the bone marrow; the signal intensity of the mass is similar to muscle on T1WI and iso- to hyperintense relative to muscle on T2WI. 4 Larger tumors may show necrosis, destruction, and infiltration of the adjacent structures. 11,12 In the assessment of solitary plasmacytoma, skeletal sur- vey is beneficial to detect lytic lesions consistent with mul- tiple myeloma and to monitor osteoblastic response to bone destruction. Computed tomographymay be more helpful in some areas to detect the extent of bone destruction, whileMR may be useful to determine the bone marrow involvement, particularly in the spine. In this setting the lesions are low in intensity and isointense on T1WI, hyperintense on T2WI and enhanced in T1W with fat saturation. 11,12 CONCLUSION We presented the imaging findings of an unusual large solitary calvarial plasmacytoma as an initial manifestation of multiple myeloma. We briefly discussed the clinical and pathological findings, as well as the progression of this entity.
Figure 4: 400x H&E sheet of plasma cells with occasional enlarged nuclei.
Figure 5: 100x CD138 plasma cells diffusely express CD138.
cases). In addition to CD56, plasmacytomas may aberrantly express CD117, CD20, CD52, CD10, and EMA. 9 Our case shows a dense and diffuse atypical plasma cell infiltrate consisting of a mixture of small normal appearing plasma cells and larger atypical occasionally pleomorphic plasma cells (Figure 4). The plasma cells are noted to both infiltrate soft tissue with prominent areas of necrosis and in- volve bone of the intramedullary space. Immunohistochemi- cal stains show a kappa-restricted plasma cell population with normal expression of CD138 (Figure 5), aberrant strong expression of CD56 and diminished expression of CD79a. The Ki-67 immunostain shows a variable proliferation in-
152 J La State Med Soc VOL 166 July/August 2014
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