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Vestibular schwannomas (VSs) are rare, occurring in approximately five per 100,000 adults a year. In circa 8% of cases, the VS is contained within the internal auditory canal, i.e. intracanalicular (iVS). Although radiosurgery is a recognised treatment modality for VSs, its full impact has not yet been characterised comprehensively. In this study, a Polish team based in Warsaw sets out to illuminate us in the specific area of radiosurgery used for iVSs. Previously they had reported 91% tumour growth control and 50% serviceable hearing preservation using radiosurgery for management of iVS. In this study, they now examine 94 patients with iVSs demonstrating growth and/or deterioration of hearing on audiometry undergoing radiosurgery between 2011 and 2015. Tumour volumes measured between 15mm3 and 350mm3, with 17% showing microcysts. Patients received between 11.5 to 13Gy, with a mean cochlear dose of 2.3Gy. Repeat MRI scanning took place 12 months post-radiosurgery, unless deterioration of symptoms was reported. Results were analysed in two age cohorts (older than 55 years versus 55 years or younger). Median tumour volume reduced in both age groups following radiosurgery. Age was not correlated to radiosensitivity or hearing preservation. Tumour proximity to the fundus and microcysts were not related to tumour growth control or hearing preservation. Gender was also not correlated to tumour growth control, hearing or facial nerve function. Post-therapy tumour pseudoprogression was seen in 10 patients: it was significantly associated with larger initial tumour volume and deterioration of hearing demonstrated on audiometry. Cochlear dose had no significant impact on hearing preservation. No impact of radiosurgery on facial or trigeminal nerve function was reported, while tinnitus reporting reduced post-radiosurgery, and vertigo was reported slightly more frequently. This study is an encouraging addition to our body of evidence in favour of using radiosurgery to control growth of iVSs. The main indicator of pseudoprogression post-therapy is higher initial tumour volume. Other than that, it continues to appear to be a sensible therapeutic strategy.

Outcomes and Prognostic Factors in the Treatment of Intracanalicular Vestibular Schwannomas Using Gamma Knife Stereotactic Radiation.
Turek G, Dzierzecki S, Obierzynski P, et al.
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Lucy Dalton

University Hospitals Birmingham, UK.

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