Background Plasmacytomas of the skull base are not commonly encountered in clinical practice, with few reported cases in the literature. They form part of the spectrum of plasma cell neoplasms and are classified as a solitary bone plasmacytoma if arising from the sphenoid bone. Its radiographic appearance can lead to misdiagnosis as one of the tumours that are more frequently seen in the skull base, especially meningiomas. Due to the risk of evolution into multiple myeloma, accurate diagnosis

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... essential. Case presentation A 56-year-old male presented to the emergency department with rapid proptosis and worsening vision in his right eye for one week's duration. Imaging studies revealed an extra-axial right sphenoid bone tumour with invasion into the temporalis muscle and orbit, leading to significant proptosis. Tumour debulking was done, but there was no improvement in vision postoperatively. Final histology was consistent with a plasmacytoma. The patient was referred to the oncologist for radiation therapy, but subsequently developed further lesions consistent with multiple myeloma. Conclusions Plasmacytomas need to be considered in the differential diagnosis of skull base tumours. Due to their excellent response to radiation, these patients should have early oncology intervention to prevent irreversible neurological deficits.