Electrically evoked auditory brainstem responses in adults and children: effects of lateral to medial placement of the nucleus 24 contour electrode array.

Objective: Previous electrophysiologic studies of electrode placement within the scala tympani in both animals and humans have shown effects on neural responses to electrical stimulation. The specific effects, however, may be dependent on electrode design, the location of an electrode along the array, and the method of perimodiolar positioning. The present study compares the effects of lateral and medial positioning of the Nucleus Contour electrode array on electrophysiologic responses in adult and pediatric subjects. Study Design: Prospective clinical study. Setting: Comprehensive Cochlear Implant Program/Tertiary Referral Center. Patients: Subjects were adults (n = 15) and children (n = 20) who were consecutively implanted at our center with the Nucleus 24 Contour device. Intervention: Rehabilitative. Main Outcome Measures: Intraoperative electrically evoked auditory brainstem responses (EABRs) were recorded within subjects for lateral and medial placement of the electrode array. Effects of electrode placement on EABR Wave V threshold and suprathreshold amplitude were measured. Results: Group analyses showed significant decreases in EABR threshold and significant increases in EABR amplitude across all electrodes with medial electrode placement. The effects differed across electrode locations for the adult and pediatric subjects. No significant changes in Wave V input/output function slope were found. Conclusion: Medial electrode placement from stylet removal with the Nucleus 24 Contour array results in an increased neural response compared with the lateral condition as demonstrated by lower threshold and larger suprathreshold amplitude of the EABR. Possible clinical implications of these findings are lower psychophysical threshold and comfortable levels with medial cochlear electrode position.