title: Factors associated with hearing preservation after Gamma Knife surgery for vestibular schwannomas in patients who retain serviceable hearing.
abstract: OBJECTIVE
  Gamma Knife surgery (GKS) has been a safe and effective treatment for small- to medium-sized vestibular schwannomas (VSs) over relatively long-term outcomes. However, even with recent radiosurgical techniques, hearing results following GKS remain unsatisfactory. The purpose of this study was to evaluate the hearing preservation rate as well as factors related to hearing preservation in patients with VSs and serviceable hearing who were treated with GKS.
  
  
  METHODS
  Among patients with Gardner-Robertson (GR) Class I or II serviceable hearing and VSs treated with GKS between 1991 and 2009, 117 were evaluable via periodic MR imaging and audiometry.
  
  
  RESULTS
  The median age at the time of GKS was 52 years. Four patients (3%) had undergone prior surgery. Fifty-six patients (48%) had GR Class I hearing and 61 (52%) had GR Class II hearing at the time of GKS. The median tumor volume was 1.9 cm(3). The median maximum and tumor margin radiation doses were 24 and 12 Gy, respectively. The median follow-up periods for MR imaging and audiometry were 74 and 38 months, respectively. The overall tumor control rate was 97.5%. Actuarial 3-, 5-, and 8-year hearing preservation rates were 55%, 43%, and 34%, respectively. On multivariate analysis, GR hearing class at the time of GKS and the mean cochlear dose affected hearing preservation significantly. In a limited number of patients who were treated using the most recent dose planning techniques and who had GR Class I hearing before treatment, the 3- and 5-year hearing preservation rates increased to 80% and 70%, respectively.
  
  
  CONCLUSIONS
  For the majority of patients with small- to medium-sized VSs, GKS was an effective and reasonable alternative to resection with satisfactory long-term tumor control. Factors related to hearing preservation included a GR Class I hearing pre-GKS and a lower mean cochlear radiation dose. To retain serviceable hearing, it is important to apply GKS treatment while patients retain GR Class I hearing.
authors.affiliation: Department of Neurosurgery, Gamma Knife Center, Komaki City Hospital, Komaki, Japan. h-toshi@komakihp.gr.jp
authors.forename: Toshinori
authors.initials: T
authors.lastname: Hasegawa
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kida
authors.forename: Takenori
authors.initials: T
authors.lastname: Kato
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Iizuka
authors.forename: Takashi
authors.initials: T
authors.lastname: Yamamoto
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D003051:Cochlea / Q000528:radiation effects / Q000601:surgery; D005260:Female; D005500:Follow-Up Studies; D006309:Hearing; D034381:Hearing Loss / Q000175:diagnosis / Q000517:prevention & control*; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000601:surgery*; D011183:Postoperative Complications / Q000175:diagnosis / Q000517:prevention & control*; D011379:Prognosis; D011829:Radiation Dosage; D016634:Radiosurgery / Q000009:adverse effects / Q000379:methods*; D055815:Young Adult