Neuro-otological findings after radiosurgery for acoustic neurinomas

To evaluate the neuro-otological complications in patients after radiosurgery for acoustic neurinomas.

Inception cohort, retrospective study.

University hospital.

A consecutive sample of 46 patients with acoustic neurinomas who underwent unilateral gamma knife radiosurgery at the University of Tokyo, Japan, between June 1990 and June 1994 were followed up by otolaryngologists for more than 3 months.

Gamma knife stereotactic radiosurgery.

Neuro-otological examinations including pure tone audiometry, auditory brain stem response, and caloric test.

Tumor growth occurred in 2 patients (4.3%). Seven (18%) of the 38 patients with preserved hearing of any extent became deaf within 1 year. In cases of gradual hearing loss, the average deterioration rate was approximately 8 dB per year. Abnormalities of auditory brain stem response preceded deafness in 2 patients. Caloric response, preserved before treatment in 13 patients, disappeared 4 to 13 months after treatment (median, 8 months) in 9 (69%) of them, whereas their hearing was preserved. Delayed facial palsy and persistent trigeminal neuropathy occurred in 10 (22%) and 7 (15%) of the 46 patients, respectively. Severe facial palsy tended to persist.

The rates of neuro-otological complications of radiosurgery are almost comparable with those previously reported from other institutions. The deafness within 1 year after treatment might be attributed to a lesion in the cochlear nerve. Hearing loss did not parallel vestibular function loss. The persistent severe facial palsy contrasts with previously reported findings. Considering the serious facial nerve complications that occurred in some of our patients, further study to disclose the risk factors for neurological dysfunction would be needed for radiosurgery to become a true, safe alternative to microsurgery.