Malignant transformation of a vestibular schwannoma to malignant peripheral nerve sheath tumor 10 years after Gamma Knife Surgery: Case report

Background and importance: Malignant transformation of vestibular schwannoma (VS) after Gamma Knife Surgery (GKS) was extremely rare, but potentially serious complication leading to poor prognosis. Small number cases have been reported but they are limited to single case report. Clinical presentation: This article presents a case of a cerebellopontine angle tumor in a 54-year-old man who had right-sided hearing disturbance which lasted for 11 years. The patient underwent tumor resection via retrosigmoid approach in May 2004 at another hospital, and subtotal removal was achieved. Pathological diagnosis was vestibular schwannoma (VS). One year later, Gamma Knife Surgery (GKS) was performed for residual tumor control. Two years after GKS, the patient was referred to our hospital and second surgical resection was performed, subtotal tumor removal was achieved and pathology showed VS. Clinical and radiological follow up were performed every 6 months. In April 2014, deterioration on clinical symptom appeared and the tumor had grown, and therefore third tumor resection via retrosigmoid approach was performed. Conclusion: Subtotal removal was achieved and pathology showed malignant peripheral nerve sheath tumor (MPNST). Although this case is rare, malignant transformation of VS after GKS should keep in mind when treating VS.