Failure of gamma knife radiosurgery for sporadic vestibular schwannomas: a systematic review and meta-analysis.

Purpose: This review aims to characterize the limitations of Gamma Knife radiosurgery (GKRS) with investigation of failure rates for primary and salvage (post-surgical) cases, identification of risk factors associated with increased rates of treatment failure, and evaluation adverse outcomes.

Methods: A systematic search (Cochrane Library, PubMed, SCOPUS, and CINAHL) of studies on sporadic vestibular schwannomas treated with Gamma Knife radiosurgery was conducted in accordance with PRISMA guidelines. Primary outcome measures included continuous measures (mean), proportions (%), and relative risks (RR) with 95% confidence intervals (CI).

Results: Forty-three studies (n = 5619 patients) were included. The proportion of GKRS failure for primary (6.4% [95% CI 4.8-7.7]) and salvage treatment (9.0% [5.9-12.8]) did not differ (2.8%, [-0.2-6.9], p = 0.06). When stratified by various thresholds on imaging, an increase of greater than 15% in a tumor's volume was seen 3.2% [2.1-4.6] which was less than rates in other volumetric thresholds of failure (p = 0.0001). Treatment edema identified by brainstem hyperintensity on imaging was the most frequent toxicity (8.8% [7.1-10.8]) with symptomatic management in about 1 in 4 cases. New onset cranial nerve adverse outcomes occurred for trigeminal neuralgia 4.9% [2.8-7.6%], trigeminal numbness 4.3% [2.7-6.2%], and temporary facial paresis 3.2% [1.3-5.9%].

Conclusion: Gamma Knife radiosurgery is an effective treatment for sporadic vestibular schwannomas with low rates of failure. Our findings suggest failure rates are not affected by treatment timing and comparable for the smaller sized tumors. Gamma Knife radiosurgery is safe with minimal adverse outcomes such as cranial nerve dysfunction, required retreatment, or other radiation toxicity.