Influence of cochlear coverage on speech perception in single sided deafness, bimodal, and bilateral implanted cochlear implant patients.

Purpose: Individualized cochlear implantation (CI) is essential to facilitate optimal hearing results for patients. Influence of cochlear coverage (CC) has been studied, however without consideration of different CI-categories, like single sided deafness (SSD), bimodal, and bilateral separately.

Methods: Retrospective analysis of preoperative CT scans was performed at a tertiary center. For each patient their individual CC with the selected electrode array was calculated off the complete CDL. Patients were categorized into SSD (n = 30), bimodal (n = 72), and bilateral CI patients (n = 29). Speech perception within the first 12 months post-implantation was compared between patient groups with shorter and longer CC. For subgroup analysis the cutoff between a shorter or longer CC was identified by the median.

Results: Cutoff between a shorter or longer CC was identified at 65% off the complete CDL for SSD and bimodal patients, and at 70% for bilateral patients. In SSD-patients longer CC was associated with better performance at activation (CC^shorter 20.0 ± 28.9% vs. CC^longer 31.5 ± 24.7%; p = 0.04) and no benefit was found with deeper insertion at 12 months. No significant benefit was found for deeper insertion in bimodal and bilateral patients.

Conclusions: Capacities of hearing performance seem to differ between SSD, bimodal and bilateral patients within the first year after implantation with regards to cochlear coverage. SSD-patients appear to benefit from deeper insertion than 65% up to 12 months after implantation. However, these results should be interpreted with caution, hence development of speech perception with CI is influenced by a whole range of factors, and bimodal and bilateral treated patients are extremely heterogenous patient groups.