Rare Presentation of Sinonasal Synovial Sarcoma With Frontal Sinus and Limited Intracranial Extension Associated With Probable Paraneoplastic Vasculitis: A Case Report.

Synovial sarcoma is a high-grade soft-tissue sarcoma that commonly affects adolescents and young adults. Involvement of the head and neck region is rare, and tumors arising from the sinonasal tract are particularly uncommon and diagnostically challenging. We report the case of a 38-year-old male who presented with head trauma and decreased consciousness following a transient neurological episode while driving. Brain computed tomography revealed a lesion involving the left anterior ethmoidal air cells with associated old cerebral infarctions. Further magnetic resonance imaging demonstrated an aggressive enhancing sinonasal mass with limited intracranial extension, associated with radiologic findings suggestive of vasculitis and acute-on-chronic ischemic insults. Histopathological evaluation showed a spindle-cell neoplasm considered most consistent with synovial sarcoma based on morphology and available immunohistochemical findings. The patient was started on neoadjuvant chemotherapy, after which the vasculitic findings showed regression, suggesting a probable paraneoplastic vasculitic association. Due to the complex anatomical location and local extension of the tumor, complete surgical resection was not initially feasible. Planned management included combined chemoradiotherapy with consideration of future surgical intervention. This case highlights the diagnostic and therapeutic challenges of sinonasal synovial sarcoma and emphasizes the importance of multidisciplinary evaluation, particularly in cases associated with unusual vasculitic and ischemic manifestations.