Conservation of residual hearing with cochlear implantation

The goals of this work were (a) to review the pre- and postsurgical auditory thresholds in a consecutive sample of cochlear implant recipients to determine the fate of residual hearing, and (b) to obtain preliminary indication of the value of a multicenter longitudinal study of residual hearing in implant patients.

Indications for cochlear implantation have been expanded to include severely hearing impaired (SHI) adults and may someday include SHI children. Implantation of individuals with more residual hearing is a concern owing to the possible development of better devices that may make use of residual hearing within the lifetime of implanted children if not that of adults. Preservation of residual hearing would be a desirable outcome of implant surgery; however, conventional thought is that implantation destroys any remaining hearing. This study was undertaken to assess if and how often conservation of hearing occurred after implantation in a sample of multichannel implant recipients.

Records of 50 profoundly hearing impaired consecutively implanted patients were examined for pre- and post-surgical audiometric results. Standard audiometric techniques were used for all testing procedures. Forty patients were considered to have some hearing conserved based on a response obtained at any one of the three speech frequencies prior to implantation. The most recent postimplantation audiometric results were used providing data from users with 1-41 months of use.

Twenty-one of 40 implanted subjects were found to have responses in at least one of the speech frequencies both pre- and postsurgery, with the majority of those displaying responses at all three frequencies. In this preliminary retrospective study, it did not appear that duration of cochlear implant use, gender, level of preoperative hearing, or length of electrode insertion were related to outcome. There were insufficient data to draw conclusions on individual devices.

Conservation of hearing occurred in approximately half of the subjects reviewed. There is no indication of what factors contributed to the preservation of hearing in those with postsurgical residual hearing or if that hearing is usable. The study does suggest that a larger multicenter longitudinal study would be of value of determine what factors may be related to conserved hearing in implanted patients.