Objective: Secondary tumorigenesis after exposure to ionizing radiation is a well-described phenomenon. The probability of developing a malignancy after stereotactic radiosurgery (SRS) is theoretically less than conventional external beam radiation therapy; however, the exact risk remains unknown. Such information is important for patient counseling when considering treatment of benign conditions such as vestibular schwannoma (VS). The objective of the current report is to describe a case of a temporal lobe gliosarcoma developing 3 years after radiosurgical treatment of a sporadic VS. Setting: Tertiary academic referral center. Patient: A 54-year-old man was diagnosed with a left-sided 1.6 cm cerebellopontine angle mass, consistent with VS. After reviewing treatment options, the patient proceeded with radiosurgery, and a tumor volume of 2.4 cm3 was treated with a marginal dose of 12.5 Gy prescribed to the 50% isodose line. Results: Serial magnetic resonance imaging (MRI) revealed good treatment response, demonstrated by central necrosis and tumor shrinkage. However, 3 years after treatment, the patient presented to the emergency department for a month long history of progressive word finding difficulties. Imaging revealed a 5 cm temporal lobe mass consistent with a high-grade glial neoplasm. He subsequently underwent stereotactic resection and final pathology confirmed World Health Organization Grade IV gliosarcoma. Conclusion: De novo malignancy after radiosurgery for VS is rare. We present only the second case of a gliosarcoma arising within the low-dose radiation field of the radiosurgery treatment plan. Some of the challenges of establishing causality between radiation treatment and secondary tumor development are discussed. The reporting of malignancy after radiation therapy, and even microsurgery, warrants continued vigilance.
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