MONITORING THE ELECTRODE POSITION DURING ACOUSTIC NEUROMA SURGERY

Objective: To obtain information about the auditory brain stem respons es during auditory brain stem implantation. Setting: Operating room du ring acoustic neuroma surgery. Methods: Electrical stimulation of the auditory system during acoustic neuroma surgery, by placement of a mon opolar or bipolar electrode on the nerve or nerve entry zone of the br ain stem, and monitoring of the evoked auditory brain stem responses ( EABR) recorded from the scalp. In some patients, a multichannel silico n electrode array was placed at the foramen of Luschka. Biphasic recta ngular 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 inte rpeak interval between the first and second peak was about 0.7 to 1.0 ms, independently of the stimulating electrode position, but the absol ute latency of the first peak increased from a minimum of 0.7 ms stimu lated at the foramen of Luschka to a maximum of 1.3 ms stimulated at t he nerve.