Malignant Transformation of a Vestibular Schwannoma Without Previous Radiation Exposure: Illustrative Case and Literature Review.

Background: Although malignant transformation of benign vestibular schwannoma (VS) preceded by irradiation has been well documented, few studies have demonstrated malignant transformation in the absence of radiation. Here, we present a rare case of the malignant transformation of a benign VS to a malignant peripheral nerve sheath tumor (MPNST) in the absence of prior irradiation. Additionally, we conducted a literature search to identify all other reported cases of MPNST arising from VS under similar conditions. Case Presentation: A 75-year-old female presented to the hospital with a 1-month history of left-sided facial numbness, loss of taste on the left side of her tongue, severe dysarthria, and recent-onset cranial nerve VI and VII palsies. MRI of the brain with and without contrast demonstrated an enlarging cerebellopontine angle mass and signs of brainstem compression. The patient underwent a left retrosigmoid craniotomy and surgical resection. Pathology and immunohistochemistry sequencing findings were consistent for MPNST with rhabdomyoblastic differentiation (malignant triton tumor). An outside review of the case by a large academic institution concurred with the diagnosis. The patient did not report any previous history of irradiation. Conclusion: A total of 11 cases, including ours, have appropriate S-100 immunochemical reactivity to confirm malignant transformation. Due to the limited number of reported cases of MPNST arising from VS without prior irradiation, information regarding pathogenesis and pathological diagnosis is scarce. We provide valuable additions to the literature, including next-generation sequencing data, to identify potentially targetable genetic changes and help elucidate the pathogenesis of MPNST.