Longitudinal Analysis of Intracochlear Electrocochleographic Amplitude Patterns in Cochlear Implant Recipients

Area of Science:

• Otoacoustic Emissions and Electrophysiology
• Auditory Neurophysiology
• Cochlear Implant Technology

Background:

• Intracochlear electrocochleography (ECochG) shows promise for monitoring cochlear function in cochlear implant (CI) recipients.
• The relationship between ECochG amplitude variations, tonotopic location, and hearing preservation (HP) after electrode array (EA) insertion requires further investigation.

Purpose of the Study:

• To longitudinally monitor maximum ECochG amplitude and its tonotopic location from EA insertion to 1 year postimplantation.
• To investigate the hypothesis that changes in ECochG amplitude or location reflect intracochlear alterations impacting residual hearing.

Main Methods:

• ECochG recordings were performed in 80 adult CI recipients with measurable residual hearing at four timepoints: intraoperatively (during and immediately after EA insertion), and postoperatively (7 weeks and 1 year).
• Measurements utilized 500 Hz tone bursts, analyzing the difference between alternating-polarity responses.
• Tonotopic locations were determined via CT scans, and hearing preservation was assessed using the HEARRING group formula.

Main Results:

• Maximum ECochG amplitudes were stable intraoperatively but significantly decreased between the immediate post-insertion and early postoperative periods.
• A >30% amplitude reduction in the early postoperative period was significantly associated with lower hearing preservation (p = 0.028).
• Nonapical peak locations intraoperatively and tonotopic shifts postoperatively were not significantly associated with hearing preservation.

Conclusions:

• Early postoperative reductions in ECochG amplitude are common and correlate with reduced hearing preservation, suggesting a need for strategies to mitigate early intracochlear reactions.
• ECochG is valuable for monitoring intracochlear processes over time, with intraoperative amplitude and location remaining stable.
• Nonapical peak patterns may indicate cochlear integrity variations rather than insertion trauma.