Stereotactic radiosurgery ensures an effective and safe long-term control of Koos grade IV vestibular schwannomas: a single-center, retrospective, cohort study

Purpose Stereotactic radiosurgery (SRS) is a standard treatment modality for vestibular schwannomas (VSs). However, there is a paucity of data on tumor control and neurological preservation for larger VSs. We aimed to investigate the long-term effectiveness of SRS for Koos grade IV compared with I-III VSs. Methods We included 452 patients with VSs (50 Koos grade IV and 402 Koos grade I‒III) who were treated with SRS at our institution from 1990 to 2021. Tumor control and functional preservation were calculated using the Kaplan–Meier method and compared between groups with the log-rank test. Results The median post-SRS follow-up period was 68 months. Progression-free survival rates were 91% at 5 and 10 years for Koos grade IV VSs, and 95% and 92%, respectively, for Koos grade I‒III VSs ( p = 0.278). In Koos grade IV VSs, functional preservation rates of the facial and trigeminal nerves were both 96% at 5 years (both 98% for Koos grade I‒III VSs; facial, p = 0.410; trigeminal, p = 0.107). Hearing preservation rates were 61% at 5 years for Koos grade IV VSs and 78% for Koos grade I–III VSs ( p = 0.645). Symptomatic transient tumor expansion was more common with Koos grade IV VSs (8.0% vs. 2.5%, p = 0.034), although all related symptoms diminished in accordance with tumor shrinkage. Conclusion SRS may contribute to long-term tumor control and adequate neurological preservation in the treatment of Koos grade IV VSs, comparable to those in the treatment of Koos grade I‒III VSs.