title: Malignant transformation of a vestibular schwannoma after gamma knife radiosurgery.
abstract: OBJECTIVE
  To 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.
  
  
  METHODS
  A 46-year-old woman presented with right facial paresthesias and imaging consistent with a right-sided vestibular schwannoma (volume approximately 18.5 cm(3)).
  
  
  RESULTS
  The 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%).
  
  
  CONCLUSIONS
  Malignant 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.
authors.affiliation: Harvard Medical School and Division of Health Sciences and Technology, Harvard-MIT, Cambridge, Massachusetts, USA.
authors.forename: Vijay
authors.initials: V
authors.lastname: Yanamadala
authors.forename: Richard W
authors.initials: RW
authors.lastname: Williamson
authors.forename: David J
authors.initials: DJ
authors.lastname: Fusco
authors.forename: Jennifer
authors.initials: J
authors.lastname: Eschbacher
authors.forename: Peter
authors.initials: P
authors.lastname: Weisskopf
authors.forename: Randall W
authors.initials: RW
authors.lastname: Porter
mesh_terms: D020295:Brain Stem Neoplasms / Q000473:pathology / Q000556:secondary; D002471:Cell Transformation, Neoplastic / Q000473:pathology*; D003399:Craniotomy; D005158:Facial Paralysis / Q000209:etiology; D017809:Fatal Outcome; D005260:Female; D006801:Humans; D019394:Ki-67 Antigen / Q000032:analysis; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local; D009422:Nervous System Diseases / Q000209:etiology; D009464:Neuroma, Acoustic / Q000473:pathology* / Q000601:surgery*; D011183:Postoperative Complications / Q000503:physiopathology; D016634:Radiosurgery / Q000009:adverse effects*
chemical_list: D019394:Ki-67 Antigen