Hearing preservation after stereotactic radiosurgery for sporadic intracanalicular vestibular schwannomas: Definite hearing preservation in “petit vestibular schwannoma”

Introduction: The mechanism of hearing loss following stereotactic radiosurgery (SRS) for vestibular schwannomas (VSs) remains unclear. There is conflicting evidence regarding cochlear nerve damage by transient volume expansion of VSs after radiosurgery and radiation-induced cochlear damage. This study aimed to investigate whether there is a specific patient population that can achieve definite hearing preservation after SRS for VSs.

Methods: A total of 40 consecutive patients with sporadic unilateral intracanalicular VSs and serviceable hearing (Gardner-Roberson [G-R] class I or II) were treated with SRS from 2009 to 2022. Survival analysis with Cox regression for hearing deterioration was performed.

Results: The median age was 54 years old. The median tumor volume was 0.093 cm3 and the median marginal dose was 12.0 Gy. Nonserviceable hearing deterioration occurred in 11 patients (27.5%), with a median onset of 17.1 months after SRS. The actuarial rates of serviceable hearing preservation were 86%, 82%, and 76% at 1, 2, and 5 years after SRS, respectively. A marginal dose >12 Gy and tumor volume >0.1 cm3 significantly increased the risk of nonserviceable hearing deterioration in the multivariate analysis. There were 13 patients with petit VSs whose tumor volume was smaller than 0.05 cm3, and 11 of them were treated by a 4-mm single shot with a marginal dose of 12 Gy. None of the 13 patients had nonserviceable hearing deterioration.

Conclusion : Petit VSs treated with a 4-mm single shot with a marginal dose of 12 Gy may achieve definite hearing preservation after SRS. The results suggests that the cause of hearing loss after radiosurgery is more due to transient volume expansion rather than cochlear radiation and also supports the treatment strategy of proactive radiosurgery for small intracanalicular VSs.