Asymmetric Insertion Depth May Hinder Academic Aptitude in Prelingual Cochlear Implant Children

OBJECTIVES: Patients with bilateral cochlear implants (CI) receive better sound localization and speech understanding in noise than unilateral CI users, but not as good as normal-hearing individuals. Recent studies found that binaural signal processing is affected by the position of the electrode and that there is often a degree of asymmetry between the CI angular depth of insertion (aDOI). Our goal was to assess the long-term effects of asymmetric (aDOI) on auditory performance, speech development, and academic aptitude in children who received bilateral CI prelingually. STUDY DESIGN: Retrospective longitudinal cohort. SETTINGS: Tertiary pediatric referral center. METHODS: Subjects included 34 prelingual deaf children who underwent bilateral simultaneous CI surgery. Depth of electrode insertion and level of asymmetry (angles) were assessed intraoperatively using x-ray analysis. Primary outcomes were the Categories of Auditory Performance (CAP) score, Speech Intelligibility Rating (SIR) score, and overall academic aptitude according to second-grade educational placement in a general education classroom versus placement in a special-needs or assisted program for hearing-impaired. RESULTS: Children with deeper insertion depths achieved better CAP scores. Children in special-needs and assisted educational programs for the hearing-impaired showed a greater degree of asymmetry (55.7±3 degrees) compared with children in general programs (29.5±2 degrees). Children with aDOI differences >40 degrees were 6 times more likely to require these assisted educational programs. No statistical difference was found between the depth of insertions and SIR results. CONCLUSIONS: An asymmetry of 40 degrees or greater is associated with a higher probability of placement in a special-needs program and/or assisted educational programs for the hearing-impaired. These data underscore the importance of carefully planning and executing electrode insertions to reduce interaural discrepancies, which may help optimize binaural hearing outcomes and support better educational prospects. Moreover, deeper insertions (aDOI ≥400 degrees) are associated with better functional audiological results (a CAP score ≥6).