Malignant transformation of vestibular schwannoma 29 years after Gamma Knife radiosurgery: illustrative case.

Background: Vestibular schwannomas are common posterior fossa tumors, often managed with stereotactic radiosurgery (SRS) due to its low invasiveness and high tumor control rates. However, malignant transformation of vestibular schwannoma (MTVS) is a rare but serious complication with a poor prognosis.

Observations: The authors present a case of MTVS occurring 29 years after initial SRS, the longest latency reported. A 68-year-old woman developed sudden facial nerve paralysis, with magnetic resonance imaging revealing tumor regrowth. Surgical removal and histopathological analysis confirmed malignant transformation, characterized by spindle-shaped atypical cells and significant p53 positivity. Despite multiple surgeries and radiation therapy, the tumor exhibited rapid regrowth and cerebrospinal dissemination, leading to a poor prognosis.

Lessons: This case underscores the critical importance of long-term monitoring after SRS, as malignant transformation can occur decades later. Additionally, it highlights the potential necessity for early intervention during malignant transformation to improve patient outcomes, despite the challenges in identifying effective treatments for MTVS. https://thejns.org/doi/10.3171/CASE24526.