Influencing the Auditory Pathway in Patients with Vestibular Schwannoma Treated with Gamma Knife Radiosurgery

Objectives: To evaluate preservation of the auditory pathway with pure-tone audiometry and brainstem evoked audiometry (BERA) in patients with vestibular schwannoma before and after treatment with Leksell gamma knife. Population and method: Twenty seven patients with vestibular schwannoma treated between 1999 and 2009. Pure-tone audiometry applying Gardner-Robertson scale and BERA were recorded. Results: During the 6-year observation, 50% patients had serviceable hearing after treatment. Before treatment, 67% patients had usable hearing level, and 93% patients had pathological BERA. Hearing deterioration was statistically significant in all frequencies (p = 0.05). lpsilateral prolongations of the latency of waves V, Ill, and I were statistically significant at 80/90dB levels (p = 0,001) in 89%, 81%, and 48% patients, respectively. Interaural pathological I-V interval difference was statistically significant in 85% patients (p = 0.001), interaural III-V interval difference reached statistical significance in 74% patients (p = 0.01). After treatment, BERA detected statistically significant difference at 80/90 dB level only for the wave V (p = 0.05). Conclusion: BERA remains reliable screening diagnostic method. Its reliability of 93% exceeds reliability of vestibular tests. Comprehensive assessment of all monitored parameters is fundamental. By incorporating pure-tone audiometry and BERA before radiosurgery, we can reliably detect whether the function of the auditory pathway is affected in patients with vestibular schwannoma of all degrees. Follow-up pure-tone audiometry is statistically significant in patients with vestibular schwannoma after gamma-knife procedure and reliably assesses preservation of the auditory pathway as well as it demonstrates distinct and statistically significant loss of serviceable hearing. Conversely, BERA remains statistically unchanged except for latency of wave V.