Plasmacytoma of the skull (CT)
Difficulty wearing helmet.
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Left superior parietal, close to the vertex lytic bone lesion with minimally postcontrast enhancing soft tissue infiltrate measuring 2.8 x 3 x 3.3 cm (AP x lat x cc). The mass is well delineated and appears extra-axial without evidence of extension into brain parenchyma. Immediately adjacent to this large lesion is a smaller area of cortical lucency which may represent a second deposit measuring only 2 x 7 mm and located entirely within the outer cortex. Other small focal lucencies have appearances consistent with venous lakes.
No other intra or extra-axial collection or acute focal abnormality identified.
Minor and patchy deep white matter and periventricular low attenuation most consistent with a sequela of chronic small vessel ischemic change.
Mucoperiosteal thickening of the ethmoid air cells, the remainder of the visualized paranasal sinuses is clear. Left mastoid air cells are partially opacified, right-sided mastoid air cells are well-aerated.
This patient went on to have a biopsy which revealed the mass to be a plasmacytoma.
The sections show a densely cellular malignant infiltrate, forming sheets and aggregates. It invades in-between bony trabeculae. The tumor cells are plasmacytoid in appearance. They have enlarged round nuclei, clumped chromatin, occasional perinuclear hofs and moderate amounts of eosinophilic cytoplasm. There is no amyloid in the background. The tumor cells are CD138 positive. Scattered cells are lambda light chain positive. Kappa light chain is negative. CD3 and CD20 are also negative. The features are those of multiple myeloma.
MRI of this patient is present as a separate case here.