Factors associated with hearing preservation after Gamma Knife surgery for vestibular schwannomas in patients who retain serviceable hearing.

Keywords: vestibular schwannoma, hearing preservation, gamma knife, outcome, radiosurgery

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     Gamma knife surgery (GKS) has been a safe and effective treatment for small- to medium-sized vestibular schwannomas over relatively long-term outcomes. However, with recent radiosurgical techniques, hearing results after GKS still remain unsatisfactory.  
     Our purpose was to evaluate the hearing preservation rate as well as factors related to hearing preservation for vestibular schwannoma patients with serviceable hearing who were treated with GKS.
     Median age at the time of GKS was 52 years. Four patients (3%) had undergone prior surgery.
     Of vestibular schwannoma patients with serviceable hearing of Gardner-Robertson (GR) class 1 or 2 treated with GKS between 1991 and 2009, 117 patients were evaluable by periodic magnetic resonance (MR) imaging and audiometry.  Fifty-six patients (48%) retained GR class 1 hearing, and 61 (52%) retained GR class 2 hearing at the time of GKS. Median tumor volume was 1.9 cm3. Median maximum and marginal doses were 24 Gy and 12 Gy, respectively.
     Median follow-up period for MR imaging and audiometry was 74 months and 38 months, respectively. Overall tumor control rate was 97.5%. Actuarial 3-, 5- and 8-year hearing preservation rates were 55%, 43% and 34%, respectively. In multivariate analysis, GR classification at the time of GKS and mean cochlear dose affected hearing preservation significantly. In limited patients treated with the most recent sophisticated techniques who retained GR class 1 hearing before treatment, 3- and 5-year hearing preservation rates increase to 80% and 70%, respectively.
     This was a retrospective study.
     For the majority of patients with small- to medium-sized vestibular schwannomas, GKS was an effective and reasonable alternative to surgical resection, with satisfactory long-term tumor control. Factors related to hearing preservation included pre-GKS GR class 1 hearing and lower mean cochlear dose.  
     To retain serviceable hearing, it is important to apply GKS treatment while patients retain GR class 1 hearing.


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