Does Size Matter? On the Role of Stereotactic Radiosurgery for Large Vestibular Schwannomas as Seen in an Institutional Experience of Gamma Knife Radiosurgery for High-Grade Tumors

Management of large vestibular schwannoma (VS) is controversial. Surgery has historically been the treatment of choice, but emerging literature suggests that definitive stereotactic radiosurgery is feasible. We report our institutional experience of control and morbidity outcomes treating Koos grade 3-4 VS with Gamma Knife radiosurgery (GKRS).An institutional review board-approved database compiled outcomes of Koos grade 3-4 VS treated by GKRS from March 2014 to January 2021 with >6 months' follow-up. Baseline symptoms per Common Terminology Criteria for Adverse Events definitions were recorded. Control rates, toxicities, and post-treatment volumetric changes were analyzed. Aggregate impairment scores (AIs) were defined by the sum of relevant Common Terminology Criteria for Adverse Events grades to categorize symptomatic burdens. Baseline and post-treatment AIs were tested for association with definitive versus adjuvant strategies.In total, 34 patients with Koos grade 3-4 VS were identified, 19 treated with definitive GKRS (GKRS-D) and 15 with adjuvant GKRS (GKRS-A). Median follow-up was 34.2 months for GKRS-D and 48.8 months for GKRS-A. Patients who received GKRS-A had greater AIs at presentation (3.73 vs. 2.11, P = 0.017). Irrespective of treatment approach, tumor control rates were 100% without instances of brainstem necrosis or shunt placement. Six of 19 patients who received GKRS-D had improved post-treatment AI, and 63% of patients who received GKRS-D and 66% of patients who received GKRS-A had tumor shrinkage >20%.In well-selected patients with Koos grade 3-4 VS, definitive stereotactic radiosurgery may be an appropriate strategy with excellent control and minimal toxicity. Our data suggest that the need for surgical decompression should be considered based on pretreatment symptom burden rather than tumor size.