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

Clinical article

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Object

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 cm3. 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.

Abbreviations used in this paper: D95 = radiation dose that includes 95% of the planning target volume; GKS = Gamma Knife surgery; GR = Gardner-Robertson; PTA = pure tone average; SRS = stereotactic radiosurgery; VS = vestibular schwannoma.

Article Information

Address correspondence to: Toshinori Hasegawa, M.D., Department of Neurosurgery, Komaki City Hospital, Gamma Knife Center, 1-20 Jobushi, Komaki, Aichi Prefecture, 485-8520, Japan. email: h-toshi@komakihp.gr.jp.

Please include this information when citing this paper: published online August 26, 2011; DOI: 10.3171/2011.7.JNS11749.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    After delineation of the cochlea on heavy T2-weighted MR images, the maximum and mean cochlear doses were shown by volume calculation of the cochlea (white square) using GammaPlan.

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    The distance from the meatal fundus to the tumor end (white square) was obtained by drawing a line (arrow) with GammaPlan.

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    Kaplan-Meier curve demonstrating the tumor expansion rate.

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    Graph showing the time courses for the median PTAs on the tumor side and the normal side. GKRS = Gamma Knife radiosurgery; N = number of patients; Y = year(s).

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    Graph showing the time courses for the differences between the pre- and post-GKS PTAs on the tumor side and the normal side.

  • View in gallery

    Kaplan-Meier curve demonstrating the hearing preservation rates plotted against time.

  • View in gallery

    Kaplan-Meier curves demonstrating the hearing preservation rates depending on the GR classification (Class I vs II, upper) and the mean cochlear dose (< 6 vs ≥ 6 Gy, lower).

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