Gamma knife surgery of vestibular schwannomas: volumetric dosimetry correlations to hearing loss suggest stria vascularis devascularization as the mechanism of early hearing loss.

Department of Otolaryngology and Communication Sciences, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
Otology & neurotology: official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology (Impact Factor: 1.44). 10/2010; 31(9):1480-7. DOI: 10.1097/MAO.0b013e3181f7d7d4
Source: PubMed

ABSTRACT Determine which variables are correlated with early hearing changes after gamma knife surgery of vestibular schwannomas (VSs).
Prospective clinical study of hearing outcomes, radiation dosimetry, conformity, and tumor size of all sporadic unilateral VS patients treated between June 2000 and July 2009.
Tertiary referral center.
: Fifty-nine VS patients with at least 6 months of follow-up data were studied.
Audiometry and imaging were performed to determine auditory thresholds, speech discrimination, and tumor size. Radiation doses to 5 volumes were measured.
Pretreatment and posttreatment comparisons were performed with regard to change in tumor size; radiation dose to specific volumes including the internal auditory canal, cochlea, basal turn of the cochlea, and modiolus; and conformity of the treatment.
The mean follow-up was 63.76 months (standard deviation, ±29.02 mo; range, 9-109 mo). The median follow-up was 65.5 months. A statistically significant association between maximum radiation dose to the cochlea volume and 3-frequency pure-tone average in patients starting with 50 dB or lesser PTA3 was demonstrated using linear regression analysis.
Longitudinal changes in hearing occur over time, with the largest changes seen in the first 12 months after treatment. With our study outcomes as basis, limiting the dose of radiation to the cochlea to no more than 4 Gy would likely reduce vascular injury to the stria vascularis and improve hearing outcomes. Shielding the cochlea during the treatment planning process would be one mechanism to accomplish this goal.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Objectives/HypothesisThe purpose of this study is to assess the effect of fractionated radiotherapy on sensorineural hearing loss using an animal model.Study DesignIn vivo animal study.Methods Ears of 25 guinea pigs were divided into three groups: control, irradiated with a total of 48 gray (Gy), and 71 Gy. Unilateral exposure of 48 Gy and 71 Gy fractionated irradiation was given for a 4-week period. Auditory brainstem response and distortion products otoacoustic emissions (DPOAE) were tested prior to irradiation and 1, 6, 10, and 16 weeks after completion of radiotherapy to assess the hearing threshold shift postradiotherapy over time.ResultsNo significant differences in hearing thresholds between the low dose radiation (48 Gy) and the control group (no radiation) underlined that 48 Gy caused no hearing deficits (P = 0.37). The higher dose (71 Gy) showed progressive deterioration of the hearing function over time. Three-way ANOVA interactions revealed significant group-time effects (F= 9.261; P < 0.0001). DPOAE analysis demonstrated hearing loss at 71 Gy without progression or recovery at all time points, predominantly in the higher frequencies tested.Conclusion The present study suggests that in the presence of sensorineural hearing loss due to high- dose fractionated radiotherapy, there is an initial sensorial component; however, the neural component is responsible for its progressivity.Level of EvidenceN/A. Laryngoscope, 2014
    The Laryngoscope 07/2014; · 2.03 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cochlear dose has been identified as a potentially modifiable contributor to hearing loss following stereotactic radiosurgery (SRS) for vestibular schwannoma (VS). (1) to evaluate the association between CT-based volumetric cochlea dose and loss of serviceable hearing following SRS; 2) to assess intra- and interobserver reliability when determining modiolar point dose using MRI and CT; 3) and to discuss the clinical significance of the cochlea dose with regard to radiosurgical planning strategy. Patients with serviceable pre-treatment hearing who underwent SRS for sporadic VS between using Gamma Knife Perfexion were studied. Univariate and multivariate associations with the primary outcome of time to non-serviceable hearing were evaluated. A total of 105 patients underwent SRS for VS during the study period, and 59 (56%) met study criteria and were analyzed. Twenty-one subjects (36%) developed non-serviceable hearing at a mean of 2.2 years following SRS (SD 1.0; median 2.1; range 0.6-3.8). On univariate analysis, pre-treatment pure tone average, speech discrimination score, AAO-HNS hearing class, marginal dose and mean dose to the cochlear volume were statistically significantly associated with time to non-serviceable hearing. However, after adjusting for baseline differences, only pre-treatment PTA was statistically significantly associated with time to non-serviceable hearing using a multivariable model. Cochlear dose is one of many variables associated with hearing preservation following SRS for VS. Until further studies demonstrate durable tumor arrest with reduced dose protocols, routine tumor dose planning should not be modified to limit cochlear dose at the expense of tumor control.
    Neurosurgery 01/2014; · 3.03 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this study was to evaluate the cochlear implant (CI) performances in neurofibromatosis type 2 (NF2) patients with bilateral vestibular schwannoma (VS) and in patients with sporadic VS in the only or better hearing ear. All patients with bilateral VS or sporadic VS in the only or better hearing ear who underwent cochlear implantation, either simultaneous to VS surgery or staged after treatment for VS, in the tumor side were chosen for the study. Postimplantation audiometric scores (sound detection, closed-set and open-set discrimination scores) and device use patterns were the main outcome measures. 15 patients were implanted. Eight patients (53 %) were NF2 and seven patients had VS in the only or better hearing ear. One patient was explanted for cerebrospinal fluid leak. In the CI-only condition, the other 14 patients obtained sound detection, 64 % of them achieving open-set discrimination (mean 70 ± 38 %) and 85 % achieving closed-set discrimination (mean 41 ± 33 %). At the last follow-up 10 patients (67 %) were using the CI. Cochlear implantation provides hearing in particular cases of patients with bilateral VS or VS in the only or better hearing ear. As long as anatomic preservation of the cochlear nerve is achieved, cochlear implantation may offer improvement in communication skills for most patients.
    Archiv für Klinische und Experimentelle Ohren- Nasen- und Kehlkopfheilkunde 12/2014; · 1.61 Impact Factor


Available from
May 27, 2014