Cochlear Implant Recipients With Electrodes in the Acoustic Region: Long-Term Hearing Preservation

It is unknown how electrode array position in the cochlea influences long-term hearing preservation for cochlear implant (CI) recipients with preserved low-frequency hearing after surgery. The aim of this study was to evaluate the influence of electrode insertion depth relative to regions of post-operative acoustic hearing and hearing preservation ≥ 1 year after CI activation.

A retrospective review of adult CI recipients of a straight electrode array from 2017 to 2022 with functional acoustic hearing preservation (≤ 80 dB HL at 250 Hz) at device activation was performed. Proximity was quantified as the angular insertion depth (AID) of the most apical contact relative to the region of preserved functional acoustic hearing. Positive values indicate placement within the functional acoustic region; negative values indicate placement basal to the functional acoustic region. Low-frequency pure tone average (LFPTA) was queried from the preoperative, device activation, and annual post-activation visits. Stepwise regression analyzed whether proximity, AID, age, biological sex, and pre-operative LFPTA were significant predictors for change in unaided hearing thresholds.

One hundred and six CI recipients met inclusion criteria. AID ranged from 330° to 717° (mean 513°, SD 79°). Proximity values ranged from -183° to 442° (mean 35°, SD 110°). None of the reviewed independent variables, including proximity, significantly predicted unaided hearing threshold shifts at the 1-year or the ≥ 3-year visits (p ≥ 0.128).

Deeper insertion depths and electrode array placement within the functional acoustic hearing region did not predispose CI recipients to delayed loss of residual hearing.