• Vijay Yanamadala, Richard W Williamson, David J Fusco, Jennifer Eschbacher, Peter Weisskopf, and Randall W Porter.
• Harvard Medical School and Division of Health Sciences and Technology, Harvard-MIT, Cambridge, Massachusetts, USA.
• World Neurosurg. 2013 Mar 1;79(3-4):593.e1-8.

ObjectiveTo report a single case of malignant transformation of a vestibular schwannoma after radiosurgery and review the growing body of literature describing patients with malignant transformation of primary benign tumors after radiosurgery, including vestibular schwannoma.MethodsA 46-year-old woman presented with right facial paresthesias and imaging consistent with a right-sided vestibular schwannoma (volume approximately 18.5 cm(3)).ResultsThe patient underwent subtotal resection followed by Gamma Knife radiosurgery (GKRS) 6 months after surgery. Initial histology showed a benign vestibular schwannoma with an MIB-1 labeling index of 5.7%. At 43 months after GKRS, the patient underwent repeat subtotal resection of a benign vestibular schwannoma (MIB-1 labeling index 7.4%). At 59 months after GKRS, she underwent a third resection, and histology showed frank malignant transformation (MIB-1 labeling index 33.8%).ConclusionsMalignant vestibular nerve tumors are extremely rare; only 18 cases have been reported in the literature. Our patient is the sixth pathologically confirmed case of malignant transformation after radiosurgery, supporting the contention that radiosurgery itself may play a causative role in transformation. In a histologically benign lesion, the presence of an elevated MIB-1 labeling index may predispose toward malignant transformation in the setting of adjuvant radiosurgery.Copyright © 2013 Elsevier Inc. All rights reserved.

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