Longitudinal Hearing Analysis In Vestibular Schwannomas Before And After Radiosurgery

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

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     Hearing preservation after radiosurgery is important.
     The aim of this study was to assess the risk of hearing loss in patients with vestibular schwannomas (VS) before and after radiosurgery.
     Between July 1997 and September 2005, 938 patients with a radiological diagnosis of unilateral VS (excluding patients with complete deafness, previous surgical interventions and neurofibromatosis type II) were treated with Gamma Knife surgery (GKS) at Timone University Hospital. Among them, 72 patients undergoing serial auditory tests at least one year before and 2 years after GKS were included in this study. 
     Annual hearing decrease rate (AHDR) before and after radiosurgery was calculated and analyzed. 
     Median dose of 12.0 Gy was prescribed to the patients. Median radiological follow-up period after GKS was 55 months. Tumor control rate was 97 % and 2 patients had to undergo subsequent GKS due to tumor progression. Median audiological follow-up terms before and after GKS were 23 and 42 months, respectively. Functional hearing preservation rate was 63%. Mean AHDR before and after radiosurgery were 3.72dB/year (95%CI: 1.99~5.45) and 3.17dB/year (95%CI: 2.23~4.11), respectively (P=0.743). Mean AHDR in early and late stage after GKS were 4.06dB/year (95%CI: 2.53~5.58) and 1.24dB/year (95%CI: 0.25~2.23), respectively (P=0.007). No prognostic factors for better hearing preservation were found in this series.
     This was a retrospective study.
     Gamma Knife surgery is capable of achieving high tumor control rate and conserving the residual hearing in patients with vestibular schwannomas. AHDR diminishes and stabilizes in two to three years after GKS.
     These results suggest that early GKS may provide better long-term preservation of residual hearing than conservative management.


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