title: Preservation of functional hearing after gamma knife surgery for vestibular schwannoma.
abstract: OBJECTIVE
  The goal of this retrospective study was to define the rates of preservation of functional hearing and growth control of vestibular schwannomas (VS) treated by gamma knife surgery (GKS) involving a consistent 12-Gy prescription dose.
  
  
  METHODS
  One hundred thirty-four patients with unilateral VS underwent GKS between 1994 and 2000. The mean magnetic resonance (MR) imaging follow-up period was 31.7 months (maximum 72 months), and the mean audiometry follow-up interval was 26.3 months (maximum 60 months). The mean marginal dose was 12 +/- 0.6 Gy. The mean maximum dose delivered to the tumor center was 25.4 Gy (range 17.4-34.3 Gy). The tumor control rate, defined as no change or a reduction in size at last follow up, was 96.7%. Of the patients studied, 97.7% remained free from the need to undergo tumor resection. Overall functional hearing preservation was 61.7%; the preservation rate for intracanalicular tumors was 63.6%, for those with an intracranial diameter less than 1.5 cm it was 54.5%, for those between 1.5 and 3 cm it was 68.2%, and for those larger than 3 cm it was 33.3%. Early in the series, three patients (2.2%) developed temporary facial weakness (House-Brackmann Grade II-III) in the posttreatment period, but this resolved within a few weeks. No case of facial weakness occurred after 1996.
  
  
  CONCLUSIONS
  The authors demonstrated the efficacy, safety, and in many ways, the advantage of GKS over microsurgery for VS. Patients harboring tumors 3 cm or smaller in intracranial diameter, regardless of their age and medical condition, should be given the option of undergoing GKS as primary treatment.
authors.affiliation: New England Gamma Knife Center and Department of Clinical Neurosciences (Neurosurgery), Brown Medical School /Rhode Island Hospital, Providence, Rhode Island 02903, USA.
authors.forename: Zachary N
authors.initials: ZN
authors.lastname: Litvack
authors.forename: Georg
authors.initials: G
authors.lastname: Norén
authors.forename: Prakash B
authors.initials: PB
authors.lastname: Chougule
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zheng
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005260:Female; D006309:Hearing; D006311:Hearing Disorders / Q000000981:diagnostic imaging / Q000517:prevention & control* / Q000601:surgery; D006801:Humans; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000000981:diagnostic imaging / Q000601:surgery*; D011859:Radiography; D016634:Radiosurgery / Q000379:methods*; D012189:Retrospective Studies