Modern Hearing Preservation Outcomes After Vestibular Schwannoma Stereotactic Radiosurgery

Abstract

Background: For patients with vestibular schwannoma (VS), stereotactic radiosurgery (SRS) has proven effective in controlling tumor growth while hearing preservation remains a key goal.

Objective: To evaluate hearing outcomes in the modern era of cochlear dose restriction.

Methods: During the years 2013 to 2018, 353 patients underwent Gamma knife surgery for VS at our institution. We followed 175 patients with pre-SRS serviceable hearing (Gardner-Robertson Score, GR 1 and 2). Volumetric and dosimetry data were collected, including biological effective dose, integral doses of total and intracanalicular tumor components, and hearing outcomes.

Results: The mean age was 56 years, 74 patients (42%) had a baseline GR of 2, and the mean cochlear dose was 3.5 Gy. The time to serviceable hearing loss (GR 3-4) was 38 months (95% CI 26-46), with 77% and 62% hearing preservation in the first and second years, respectively. Patients optimal for best hearing outcomes were younger than 58 years with a baseline GR of 1, free canal space ≥0.041 cc (diameter of 4.5 mm), and mean cochlear dose <3.1 Gy. For such patients, hearing preservation rates were 92% by 12 months and 81% by 2 years, staying stable for >5 years post-SRS, significantly higher than the rest of the population.

Conclusion: Hearing preservation after SRS for patients with VS with serviceable hearing is correlated to the specific baseline GR score (1 or 2), age, cochlear dose, and biological effective dose. Increased tumor-free canal space correlates with better outcomes. The most durable hearing preservation correlates with factors commonly associated with smaller tumors away from the cochlea.

FIGURE 1.

Constructive interference in steady state sequence MRI demonstrating the separation of intracanalicular and extracanalicular tumor segments (red line) of a patient with a large (A: 0.07 cc) and small (B: 0.001 cc) free canal space (yellow outline). Both patient A and B (69 and 58 years) had good serviceable hearing at baseline and exposed to mean cochlear doses of 3.7 and 3.5 Gy with maximal doses of 7.8 and 7.7 Gy, respectively. Over time after radiosurgery, patient A had good and stable hearing while patient B showed significant hearing loss.

FIGURE 2.

Time to serviceable hearing loss from the day of stereotactic radiosurgery by tumor-free canal space, below or above 0.041 cc (n = 92 and n = 70, respectively, Kaplan–Meier, log-rank test).

FIGURE 3.

Time to serviceable hearing loss from the day of stereotactic radiosurgery by cochlear dose, below or above 3.1 Gy (n = 65 and n = 108, respectively, Kaplan–Meier, log-rank test).