Intraoperative Real-time Cochlear Response Telemetry Predicts Hearing Preservation in Cochlear Implantation

To monitor cochlear function during cochlear implantation and determine correlations with postoperative acoustic hearing.

Cochlear response telemetry measures cochlear function directly from cochlear implant electrodes. We have adapted this system to provide real-time cochlear response telemetry (RT-CRT) monitoring of a patient's acoustic hearing as the cochlear implant electrode array is inserted.

Eighteen subjects (1 child and 17 adults) with sloping high frequency hearing loss were implanted with Cochlear Ltd slim straight arrays (CI422/CI522). Tone bursts (500 Hz, 100-110 dB) were presented at 14 Hz continuously during the array insertion. RT-CRT amplitudes were correlated with surgical manoeuvres recorded on the video from the operating microscope and with postoperative pure tone audiograms.

Despite an excellent overall rate of complete or partial hearing preservation (79%), RT-CRT identified that in 47% of these implantations there was transient or permanent reduction in the amplitude of the cochlear microphonic (CM). Patients with a preserved CM at the end of insertion had on average 15 dB better low-frequency hearing preservation. The CM amplitude was most vulnerable during the last few millimeters of insertion or when inadvertent movement of the array occurred after full insertion. Physical contact/elevation of the basilar membrane is hypothesized as a likely mechanism of hearing loss rather than overt physical trauma.

RT-CRT can be used to predict early postoperative hearing loss and to potentially refine surgical technique. In the future, feedback of RT-CRT may prove to be a valuable tool for maximizing preservation of residual hearing or providing feedback on electrode contact with the basilar membrane.