Clinical Applications of Intracochlear Electrocochleography in Cochlear Implant Users With Residual Acoustic Hearing

Abstract

We herein review the use of electrocochleography (ECoG) to assess peripheral auditory system responsiveness in a growing population of cochlear implant (CI) users with preserved hearing in ears with implants. Twenty-eight recently published intracochlear ECoG articles were thoroughly reviewed to investigate the prognostic utility of intraoperative ECoG monitoring to assess hearing preservation, and the clinical applicability of postoperative ECoG for estimating audiometric thresholds and monitoring longitudinal changes in residual acoustic hearing in patients with EAS. Intraoperative ECoG studies have focused on monitoring the changes in the cochlear microphonics (CM) amplitudes during and after electrode insertion. Mixed results have been reported regarding the relationship between changes in CM amplitude in the operating room and changes in hearing thresholds after surgery. Postoperative ECoG studies have shown that CM and auditory nerve neurophonics thresholds correlate significantly with behavioral thresholds. ECoG thresholds sensitively detect changes as residual acoustic hearing decreases over time in some CI users. This indicates its potential clinical value for monitoring the post-implantation status of the peripheral auditory system. Intracochlear ECoG can provide real-time intraoperative feedback and monitor postoperative hearing preservation in a growing population of CI users.

Keywords: Cochlear implant; Electro-acoustic stimulation; Electrocochleography.

Fig. 1.

An example of electrocochleography responses (electrogram) recorded using a 500 Hz tone burst. CM, cochlear microphonic; ANN, auditory nerve neurophonic; CAP, compound action potential; SP, summating potential.

Fig. 2.

An example of CM and ANN recordings from a single CI user. CM, cochlear microphonic; CI, cochlear implant; DIF, difference response; ANN, auditory nerve neurophonic; SUM, summed response; CAP, compound action potential. Data excerpted from Kim et al. Hear Res 2018;370:304-15 [17].

Fig. 3.

Correlations between electrocochleography thresholds and postoperative audiometric thresholds. CM, cochlear microphonic; DIF, difference response; ANN, auditory nerve neurophonic; SUM, summed response. Data excerpted from Kim et al. Hear Res 2018;370:304- 15 [17].