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 neuro-otological 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 low-tone 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.