High-Grade Sarcoma Arising within a Previously Irradiated Vestibular Schwannoma: A Case Report and Literature Review.

Vestibular schwannomas are benign tumors of the cerebellopontine angle that are often treated with radiation therapy. Radiation therapy maintains good tumor control rates but involves a small risk of radiation-induced malignancies. We present a case of high-grade sarcoma arising within a previously irradiated vestibular schwannoma and a literature review of this rare but important clinical entity. A 66-year-old woman presented with rapid clinical and radiographic deterioration 17 years after receiving stereotactic radiosurgery for vestibular schwannoma. After resection, pathology revealed a high-grade sarcoma arising within a conventional schwannoma. After further decline and tumor growth, the patient died of her disease 7 months postoperatively. Literature review was performed using PubMed and EMBASE databases and key words "vestibular schwannoma," "acoustic," "triton," "malignant," "sarcoma," "malignant peripheral nerve sheath tumor," "radiation," and "radiosurgery." All previous cases and the clinical circumstances related to these radiation-induced malignancies were assessed and quantified. The systematic review yielded 20 prior cases of radiation-induced malignant transformation of a vestibular schwannoma in patients without neurofibromatosis. Most tumors (60%) transformed into malignant nerve sheath tumors. At the time of presentation, 70% of patients had new cranial neuropathies, and all had evidence of tumor growth with brainstem compression. Prognosis was poor with mean time to death of 7.6 months. Radiation-induced malignant transformation of vestibular schwannomas is a rare but important clinical entity. Given its scarcity, the risk of malignancy should not sway initial management, but rapid clinical deterioration and radiographic growth during follow-up should prompt consideration of malignant transformation. [ABSTRACT FROM AUTHOR]