Hearing loss and changes in transient evoked otoacoustic emissions after gamma knife radiosurgery for acoustic neurinomas

Objective: To evaluate the neuro-otological effects of gamma knife radiosurgery in patients with acoustic neurinoma. Design: Prospective study. Setting: University hospital in Milan, Italy. Patients: Thirty consecutive patients with acoustic neurinoma who underwent gamma knife radiosurgery. Intervention: Gamma knife radiosurgery. Main Outcome Measures: Results of neurootological tests, including pure-tone audiometry, auditory brainstem responses, and transient evoked otoacoustic emissions, during a 2-year follow-up. Results: Three patients showed slight tumor growth, 1 complained of a transient facial disturbance, and 5 complained of mild trigeminal disturbances. Seven of the 26 patients with a measurable threshold before radiosurgery experienced a 2-year decrease of more than 20 dB in at least 1 hearing level, and 2 of these became deaf in the affected ear. The analysis of auditory brainstem responses showed no significant increase in mean wave V latency after radiosurgery, but intensity of transient evoked otoacoustic emissions worsened in 9 of the 12 patients who had them before treatment. A statistically significant correlation was found between the 2-year decrease in lowtone average, pure-tone average, and high-tone average hearing levels and the 2-year decrease in transient evoked oacoustic emissions (P<.001, P=.008, and P<.001, respectively), and between the 2-year decrease in high-tone average hearing and the maximal cochlear dose (P=.03). Conclusions: Although most patients had only a slight fluctuation of their hearing threshold after gamma knife radiosurgery, several experienced a remarkable hearing worsening. Hearing impairment was found to be mainly due to cochlear irradiation and maximal cochlear dose, which was correlated to hearing loss.