The Effect of Cochlear Coverage on Auditory and Speech Performance in Cochlear Implant Patients

Objective: To determine the effect of cochlear coverage on audiological and speech parameters in patients with cochlear implants. Previous work has investigated the effect of tailoring electrode size to a cochlear implant recipient's individual cochlear duct length (CDL). However, no clear relationship has been found between speech development and the extent of electrode insertion, and the benefits of apical stimulation are not yet clear. Methodology: In this retrospective study, we assessed the effect of cochlear coverage on audiological and speech performance. Participants were prelingually deaf children who received cochlear implants between June 2013 and December 2014 under the care of a single cochlear implant surgeon. Cochlear coverage was estimated for each ear according to electrode type, depth of insertion, and the number of active electrodes. Electrode type and length were determined by the individual's CDL, measured by computed tomography (CT), and full insertion was documented intraoperatively. The number of active electrodes was recorded using intraoperative audiological response telemetry. Audiological assessments were obtained 6 months and 1 year postoperatively. Results of the categories of auditory performance-II and speech intelligibility rating scales were obtained after 3 years. Patients were divided into two groups based on their cochlear coverage and their audiological and speech outcomes were compared. Results: Of the 97 children recruited, 47 were girls. Temporal bone CT scans showed the right and left mean CDLs among girls were 27.7 and 27.9 mm, respectively, and 29.2 mm for both ears in boys. For each sex, the right and left CDLs did not differ significantly (p = 0.07). Twenty patients were lost to follow-up, leaving 77 patients (120 ears), which were divided into groups according to cochlear coverage (complete vs. incomplete). Significant between-group differences were not found in assessments of audiology, categories of auditory performances, or speech intelligibility ratings after 3 years. Conclusion: Audiological parameters do not differ according to the degree of cochlear coverage, specifically for low-frequency tones. Speech parameters are also comparable. Therefore, complete cochlear coverage does not appear to provide significant benefit over incomplete coverage for prelingually deaf cochlear implant recipients.