Preservation of Residual Hearing in Cochlear Implantation

Objectives: Many cochlear implant candidates have measurable hearing prior to implantation. Recent reports indicate that residual hearing can be preserved. By comparing pre- and postimplantation auditory thresholds, this study examines the Texas Children’s Hospital experience with conservation of residual hearing. Methods: Children with bilateral profound sensorineural hearing, implanted at least 6 months prior to this study, were eligible for enrollment. A multi-channel device was implanted by the same surgeon in each patient using a round window approach. Preimplantation auditory steady-state responses (ASSR) were available for each patient. Postoperative ASSR were obtained and compared to preimplant thresholds. The nonimplanted ear served as control. Results: Twelve patients (mean age, 4.9 years; 42% male) were studied. Paired t tests indicated no statistically significant differences (P < 0.05) between the pre- and postimplant ASSR thresholds at 250, 500, 1k, 2k, 4k, and 8k Hz in the implanted ear. There was no difference (P < 0.05) over the same time period for ASSR thresholds in the nonimplanted control ears at the same frequencies. Conclusion: With the use of a round window approach, by 6 months postimplantation, there is no statistically significant change in auditory function in the implanted ear. Furthermore, by using the nonimplanted ear as a control, this study demonstrates the ASSR to be a stable measure over time. Preservation of residual hearing requires serious consideration as technological advances in electrode development and changing selection criteria for implantation occur.