Monitoring the electrode position during acoustic neuroma surgery.

OBJECTIVE

To obtain information about the auditory brain stem responses during auditory brain stem implantation.

SETTING

Operating room during acoustic neuroma surgery.

METHODS

Electrical stimulation of the auditory system during acoustic neuroma surgery, by placement of a monopolar or bipolar electrode on the nerve or nerve entry zone of the brain stem, and monitoring of the evoked auditory brain stem responses (EABR) recorded from the scalp. In some patients, a multichannel silicon electrode array was placed at the foramen of Luschka. Biphasic rectangular current pulses were applied, and EABRs were recorded.

RESULTS

Usually the derived potentials consisted of three peaks with a latency below 4 ms. Sometimes we got a complex of two or more peaks. The interpeak interval between the first and second peak was about 0.7 to 1.0 ms, independently of the stimulating electrode position, but the absolute latency of the first peak increased from a minimum of 0.7 ms stimulated at the foramen of Luschka to a maximum of 1.3 ms stimulated at the nerve.