Effectiveness of Microanatomy-based Low-dose Radiosurgery of Vestibular Schwannomas for Hearing Preservation in Patients with Neurofibromatosis Type 2: A Retrospective Analysis of 16 Cases

INTRODUCTION: The role of stereotactic radiosurgery (SRS) of vestibular schwannomas (VS) in patients with neurofibromatosis type 2 (NF2) is still not established well. The objective of this retrospective study was evaluation of effectiveness of proactive microanatomy-based low-dose SRS for serviceable hearing preservation in such cases. METHODS: Study cohort included 16 NF2-asociated VS in 13 patients, who underwent SRS between January 2002 and March 2022. Median tumor volume was 0.56 cc (range, 0.12 - 2.75 cc). Hearing on the side of treated tumor corresponded to Gardner-Robertson classes I (12 cases) or II (4 cases). Special emphasis was consistently put on creation of the highly conformal and selective radiosurgical treatment plan based on precise evaluation of the local microanatomy with attempted identification of the nerve of origin and chronological trajectory of growth of the tumor, allowing to estimate the direction and magnitude of the facial nerve and other cranial nerves shift and to prevent them from excessive irradiation. The prescription dose of 12 Gy (15 cases) or 11 Gy (1 case) was delivered at 50% (13 cases) or >50% (3 cases) isodose line. Median maximal cochlear dose was 5.8 Gy (range, 2.2 - 8.2 Gy). RESULTS: Median post-treatment follow-up was 88 months (range, 30 - 226 months). Actuarial proportions of cases without hearing deterioration at 3, 5, and 10 years after SRS were, respectively, 0.81 ± 0.10, 0.67 ± 0.12, and 0.56 ± 0.14. Actuarial proportions of cases with serviceable hearing preservation at 3, 5, and 10 years after SRS were, respectively, 0.81 ± 0.10, 0.81 ± 0.10, and 0.67 ± 0.15. Gardner-Robertson class I hearing at the time of treatment and used prescription isodose of 50% showed statistically significant associations with subsequent hearing preservation without deterioration (P = 0.0242 and 0.0024, respectively) and with serviceable hearing preservation (P = 0.0047 and 0.0020, respectively). Specifically, actuarial proportions of cases with serviceable hearing preservation at 5 years after SRS in cases with Gardner-Robertson classes I and II hearing were 1.00 and 0.25 ± 0.22, respectively (P = 0.0009). CONCLUSION: Gardner-Robertson class I hearing at the time of SRS for VS in patients with NF2 is associated with significantly higher chances of serviceable hearing preservation during subsequent long-term follow-up. It may advocate use of early proactive microanatomy-based low-dose SRS in such cases, particularly in young individuals.