Rapid Spontaneous Malignant Transformation of a Radiation-Naïve Vestibular Schwannoma

Malignant transformation of sporadic vestibular schwannomas (VS) is extremely rare in the absence of neurofibromatosis type 2 (NF2) or prior radiotherapy history. We present the case of a 36-year-old male patient with no familial predisposition who underwent primary resection for a benign VS. Two months postoperatively, the patient presented with acute hemorrhage at the surgical site, necessitating an urgent repeat craniotomy. Pathologic examination of the resected specimen revealed a high-grade malignant schwannoma (MPNST) with a Ki-67 index of 80% and absent S100 expression, confirming malignant transformation. This case demonstrates that sporadic VS can undergo spontaneous, ultrarapid malignant transformation independent of NF2 or radiotherapy, underscoring the need for vigilance during postoperative follow-up, even after an initial benign diagnosis.