Intraoperative test of auditory nerve function.

OBJECTIVE

To develop a preoperative objective test of auditory nerve function for the assessment of cochlear implant candidacy, especially in children.

PATIENTS AND METHODS

We stimulated electrically with a ball electrode before insertion of the implant. First the stimulus was applied bipolar between the promontory and the round window. To record auditory brain stem responses (EABRs) very high stimulus intensities were needed, which was not possible in all patients.

RESULTS

By stimulation in the basal turn of the cochlea, evoked potentials could be derived. Although in some patients the facial nerve was stimulated as a side effect, auditory evoked potentials could be recorded. A facial muscle artifact can be differentiated from the EABRs by latency and the slope of the input-output function.

CONCLUSION

For the present, the only reliable test seems to be the EABR recording stimulated within the cochlea.