Temporoparietal Scalp Intravenous Schwannoma: Rare Subcutaneous Soft Tissue Mass in an Unusual Location

Schwannomas, or neurilemmomas, are benign nerve sheath tumors of Schwann cell origin, sometimes associated with neurofibromatosis type 2 (NF2) and schwannomatosis. Intravenous schwannomas are exceedingly rare, pose diagnostic challenges due to their unusual location within blood vessels and lack of surrounding perineurium. A 69-year-old male presented with a subcutaneous mass behind the left ear in the upper temporoparietal scalp, firm and mobile, 5 × 7 cm², gradually growing for 15 years. Past physical examinations considered the lesion a cutaneous inclusion cyst. Surgical extirpation revealed a solid tumor adherent to the underlying fascia and muscle easily removed along surgical planes. Histopathology showed a well-circumscribed, spindle cell lesion, S100 protein positive, with foci of hypercellular (Antoni A) and hypocellular (Antoni B) areas, with distinctive Verocay bodies pathognomonic for schwannoma. EMA was negative at the periphery, demonstrating a lack of perineurium, supporting that the schwannoma was not within a nerve bundle. However, a Verhoeff van Gieson elastic tissue stain revealed a circumferential single internal elastic lamina, while CD31 marked the endothelial cells lining a stretched vein encasing the tumor, confirming an intravenous schwannoma.