Abstract
BACKGROUND: Hearing success in bimodally hearing patients with a cochlear implant (CI) and a hearing aid (HA) exhibits different results: while some benefit from bimodal CI and HA, others do not. OBJECTIVE: The aim of this study was to investigate hearing success in terms of speech perception in bimodally fitted patients in relation to the cochlear coverage (CC) of the CI electrodes. MATERIALS AND METHODS: Using the OTOPLAN software (CAScination AG, Bern, Switzerland), CC was retrospectively measured from CT scans of the temporal bone of 39 patients, who were then categorized into two groups: CC ≤ 65% (CC(500)) and CC > 65% (CC(600)). Monaural speech intelligibility for monosyllables at a sound pressure level (SPL) of 65 dB in open field was assessed at various timepoints, preoperatively with HA and postoperatively with CI, and compared between the groups. In addition, speech intelligibility was correlated with CC in the entire cohort before surgery and during follow-up (FU). RESULTS: Overall, no significant differences in speech intelligibility were found between CC(500) and CC(600) patients at any of the FU timepoints. However, both CC(500) and CC(600) patients showed a steady improvement in speech intelligibility after implantation. While CC(600) patients tended to show an earlier improvement in speech intelligibility, CC(500) patients tended to show a slower improvement during the first 3 months and a steeper learning curve thereafter. The two patient groups converged during FU, with no significant differences in speech intelligibility. There was no significant relationship between unimodal/unilateral free-field speech intelligibility and CC. However, patients with a CC of 70-75% achieved maximum speech intelligibility. CONCLUSION: Despite a nonsignificant correlation between CC and speech discrimination, patients seem to reach their maximum in unimodal/unilateral speech understanding mainly at 70-75% coverage. However, there is room for further investigation, as CC(500) was associated with a shorter cochlear duct length (CDL), and long and very long electrodes were used in both groups.