Sporadic sarcoma arising from a previously resected benign vestibular schwannoma without neurofibromatosis or radiosurgery: illustrative case.

backgroundVestibular schwannomas (VSs) are common benign tumors of the cerebellopontine angle, often treated with surgery or stereotactic radiosurgery to preserve nerve function. Malignant transformation of VS (MTVS) is exceedingly rare and has been primarily associated with neurofibromatosis type 1 (NF1), neurofibromatosis type 2-related schwannomatosis (NF2-SWN), or prior radiation exposure. However, cases of MTVS occurring without these risk factors are rare and remain poorly understood. OBSERVATIONS: A 58-year-old woman without neurofibromatosis underwent subtotal VS resection in 2019, with stable residual tumor and no adjuvant treatment. In 2023, she developed acute neurological decline, and imaging suggested malignant transformation or a new tumor. Surgery confirmed a high-grade neoplasm, likely leiomyosarcoma or malignant peripheral nerve sheath tumor, with genetic analysis revealing no NF1 or NF2-SWN mutations. She received adjuvant stereotactic radiation therapy, and at the 3-month follow-up, imaging showed stable residual disease. However, she continued to experience persistent neurological deficits, including facial weakness, ataxia, and intention tremor, with a Karnofsky Performance Scale score of 60%. LESSONS: MTVS is extremely rare without neurofibromatosis or prior radiation therapy, potentially driven by surgical inflammation or unidentified genetic alterations. While increased surveillance after subtotal resection may be considered, more research is needed to identify predictive markers and guide clinical management. https://thejns.org/doi/10.3171/CASE251003.