Critical Factors for Binaural Hearing in Children with Bilateral Sequential Cochlear Implantation: First Implant Performance and Inter-Implant Interval

Objectives: This study evaluated the influence of the performance of the first cochlear implant (CI-1) on the second implant (CI-2) and the significance of inter-implant intervals in children with sequential cochlear implantation. Method: Thirty-four patients were included for speech perception outcome and 38 patients were included for subjective hearing satisfaction in daily life in this study. The patients were classified into 3 groups according to inter-implant interval: group I, <4 years; group II, 4–7 years; group III, >7 years. Open-set speech perception scores before and at 3, 6, 12, and 24 months after the second implantation was compared among the CI-1, CI-2, and bilateral CI conditions. Subjective hearing benefits in daily life were measured using a questionnaire of Speech, Spatial, and Qualities of Hearing Scale (SSQ) for parents of children with impaired hearing, and device use and preference were evaluated (by phone interview.) Results: The speech perception of children using the CI-2 only improved quickly within 3 months postoperatively and were similar to those using the CI-1 only. The results of monosyllabic and disyllabic word tests using CI-2 at 3 months after second implantation were not significantly different from those in patients using the CI-1 only. In the sentence test, the scores using the CI-2 only were not significantly different from those using the first implant only at 6 months after second implantation. SSQ scores were similar among groups and the worst score in each section was shown from the questions about performance under noisy conditions in each section. Device usage habits showed that 17 (44.7%) and 16 (42.1%) patients preferred bilateral and the CI-1, respectively. Only 5 (13.2%) patients wanted the CI-2 rather than the CI-1. While group I and II showed a prominent positive attitude to bilateral use, group III, for which the inter-implant interval was 7 years or more, showed a definite preference for the CI-1 (p < 0.01). Conclusions: Functional binaural benefits were achieved in patients who were good performers with the CI-1 after the second implantation irrespective of the inter-implant interval. Sequential CI should be strongly recommended for patients with unilateral CI showing a good performance.