Natural course of residual hearing preservation with a slim, modiolar cochlear implant electrode array

Understanding residual hearing preservation and its natural course following cochlear implantation is important for developing rehabilitation strategies for hearing loss. However, non-uniform evaluation criteria and varying surgical skills pose challenges in fair comparison of the effect of different electrodes on residual hearing preservation. We compared the effect of a slim modiolar electrode (SME) and a slim straight electrode (SSE), implanted by a single surgeon, on progression of residual hearing using different parameters, based on cross-sectional and longitudinal audiological analyses.

Patients with preoperative low-frequency pure-tone average (LFPTA) ≤85 dB at 250 and 500 Hz and who underwent minimally traumatic surgical techniques were included. The progression of residual hearing using threshold shifts, hearing preservation rate according to the HEARRING classification, and maintenance of functional low-frequency hearing potentially qualifying for a hybrid stimulation was analyzed up to five time points throughout the 1-year follow-up period.

Threshold shifts and hearing preservation rates according to the HEARRING classification of the electrodes were comparable from 3 months through 12 months postoperatively. Maintenance of functional low-frequency hearing, required for the usage of a hybrid stimulation, was similar for both electrodes. A substantial proportion of implantees with SME use a hybrid stimulation, resulting in long-term use. However, a difference in the pattern of postoperative residual hearing preservation between the two electrodes is possible, probably due to differences in their physical characteristics and location. Specifically, correlation analysis exhibited that significantly less tight modiolar proximity negatively affect the residual hearing preservation, albeit only at 3 months postoperatively, among patients with the SME.

Collectively, both SME and SSE implantation showed favorable residual hearing preservation. Our findings further refine the recently proposed hearing preservation with the SME and suggest that the physical characteristics and location of electrodes, in terms of electrode-to-modiolus distance, could affect loss of acoustic hearing in various ways.