A rare differential diagnosis for cause of proptosis: skull plasmacytoma.

True solitary plasmacytoma of the skull without signs of systemic myelomatosis is very rare as is orbital involvement. It can be part of generalized disease (multiple myeloma) or localized disease, presenting as orbital tumor. We describe a case of solitary osseous plasmacytoma of the orbit. This 40-year-old man presented with a four month history of proptosis of the left eye, swelling in the left orbito-temporal region with a mild decrease in visual acuity. Multidetector row computed tomography scan showed a geographic osteolytic, well-demarcated lesion involving the greater wing of the sphenoid bone showing homogeneous contrast enhancement with extra-axial extension to the middle and anterior cranial fossa extension with extraconal extension into the orbit at the right side. Fine needle and later biopsy of the lesion revealed plasmacytoma.