Effects of bilateral cochlear implants in children: Timing of second surgery and the significance of wearing bilateral cochlear implants in Japan

Objective: This study aims to evaluate the speech perception with first, second, or bilateral cochlear implants (CI) and to reveal the effects of wearing bilateral CI in children. Methods: After reviewing the medical records, a total of 19 children who underwent bilateral cochlear implantation serially between 2012 and 2015 at Kyoto University Hospital (tertiary referral center) were included in this study. All patients had no delay in language development. The study group comprised nine boys and ten girls, and their age ranged from 3 years 8 months to 12 years 5 months when they underwent the tests in this study. The mean and median ages were 8 years 6 months and 9 years 2 months, respectively. We measured the appropriate signal/noise ratio (SNR) to test speech perception of Japanese language in noise by testing the hearing ability of unilateral CI patients with or without noise and by surveying the sound environment in a classroom of a mainstream elementary school. Speech perception in quiet and noise and the left-right localization ability were examined using first, second, or bilateral cochlear implants in all patients. Results: Considering the results of hearing ability tests with noise and the SNR of the elementary school classrooms, we decided to use SNR of +10 dB to evaluate the speech perception ability in noise. The speech perception ability using the second CI was significantly worse in patients undergoing second cochlear implantation after 7 years old than in those who underwent surgery before 3.5 years old. Moreover, patients undergoing second cochlear implantation before 7 years old showed significantly better left–right localization of high-frequency sound. Conclusions: Second cochlear implantation before 7 years old is a critical factor in acquiring beneficial speech perception ability with the second CI and sound localization ability with the bilateral CI.