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Case Reports

Abstract

Background: Schwannomas, or neurilemmomas, are benign nerve sheath tumors of Schwann cell origin sometimes associated with neurofibromatosis type 2 (NF2) and schwannomatosis. Intravascular schwannomas are exceedingly rare, and pose diagnostic challenges due to their unusual location within blood vessels and lack of surrounding perineurium. 

Objective: Discuss the histopathologic features and differential diagnosis of an intravascular schwannoma initially suspected to be an inclusion cyst.

Case Presentation:  A 69-year-old male presented with a subcutaneous mass behind the left ear in the upper temporal/parietal skull area, gradually growing for 15 years. Physical examination revealed the mass to be firm and mobile, measuring 7 x 5 cm². Surgical extirpation revealed a solid tumor adherent to the underlying fascia and muscle, which was easily removed along surgical planes. Histopathological examination showed a well circumscribed, spindle cell lesion featuring hypercellular (Antoni A) and hypocellular (Antoni B) areas, with distinctive Verocay bodies pathognomonic for schwannoma. The spindle cells tested strongly positive for S100 protein, further confirming a schwannoma. EMA was negative at the periphery, demonstrating a lack of perineurium, supporting that the schwannoma was not within a nerve bundle. However, CD31 marked the endothelial cells lining the stretched vein encasing the tumor, confirming an intravascular schwannoma. Differential diagnoses included angioleiomyoma, intravascular lobular capillary hemangioma, and intravascular glomus tumors.

Conclusion: Intravascular schwannomas are a rarely documented phenomenon. By reporting this case into the growing literature, healthcare providers are able to include it into their differential diagnosis when considering atypical presentations of schwannomas not associated with a nerve.