Radiation-Induced Sarcoma in a Large Vestibular Schwannoma Following Stereotactic Radiosurgery: Case Report

BACKGROUND AND IMPORTANCE: Stereotactic radiosurgery (SRS) has been employed with increasing frequency in the treatment of benign intracranial tumors. While the risk for radiation-induced malignancy has been well studied for fractionated external beam radiation, reports of SRS-associated malignancy have only begun to emerge over the past 10 years. CLINICAL PRESENTATION: We present a case of a rapidly enlarging, presumed sporadic vestibular schwannoma in a 51-year-old man treated with SRS. Serial imaging over the next 7.5 years demonstrated good radiographic response with consistent involution of the tumor. The patient then developed rapid neurologic deterioration and sustained tumor growth on follow-up imaging. The tumor was resected via a translabyrinthine approach, and pathologic analysis demonstrated undifferentiated high-grade pleomorphic sarcoma (UHGPS). CONCLUSION: This is the first report of undifferentiated high-grade pleomorphic sarcoma (formerly called malignant fibrous histiocytoma) following SRS. This case demonstrates the difficulty of establishing malignant degeneration of a neoplasm following SRS without pretreatment tissue diagnosis. Patients with presumed benign tumors should be counseled about the rare risk of malignant transformation prior to undertaking SRS.