Intracochlear Recording of Electrocochleography During and After Cochlear Implant Insertion Dependent on the Location in the Cochlea

The potential of electrocochleography in explaining the variability in cochlear implant outcomes: a scoping review

OBJECTIVE

This review aimed to catalogue the literature exploring electrocochleography (ECochG) as a potential tool to improve pre-implantation counselling for cochlear implant (CI) recipients. Specifically, it examined the correlation between ECochG responses and speech perception to assess whether these measurements could explain some of the variability in CI outcomes.

DESIGN

Scoping review.

STUDY SAMPLE

Sixteen studies were included in this review, 14 of which investigated the correlation between ECochG total response (ECochG-TR) and speech perception outcomes. Additionally, four studies focused on specific components of ECochG-TR in relation to speech perception outcomes.

RESULTS

Despite several limitations, most studies found that ECochG-TR significantly contributed to the variability in speech perception outcomes, explaining between 16-59% of the variance. The few studies correlating specific ECochG responses, such as cochlear microphonics, summating potential, auditory nerve neurophonics, and compound action potential, with CI outcomes, reported inconsistent results.

CONCLUSION

This review demonstrated that ECochG-TR can explain a significant portion of the variance in CI outcomes. However, due to the numerous limitations, further research is needed on the correlation between specific ECochG responses and CI outcomes. While ECochG measurements hold value in a research context, they have limited utility in clinical practice for pre-implantation counselling.

Does the audiogram shape influence the intracochlear recording of Electrocochleography during and after cochlear implantation?

During cochlear implant (CI) surgery, it is desirable to perform intraoperative measurements such as Electrocochleography (ECochG) to monitor the inner ear function and thereby to support the preservation of residual hearing. However, a significant challenge arises as the recording location of intracochlear ECochG via the CI electrode changes during electrode insertion. This study aimed to investigate the relationships between intracochlear ECochG recordings, the position of the recording contact within the cochlea relative to its anatomy, and the implications for frequency and residual hearing preservation. Intraoperative ECochG recordings were conducted using the CI electrode (MED-EL) during the insertion of hearing preservation electrodes and after the insertion process. Recordings were continuously conducted using the most apical electrode (contact 1) during insertion. After insertion, the recordings were performed on all different electrode contacts. The electrode location in the cochlea during insertion was estimated using mathematical models and preoperative clinical imaging, while the postoperative electrode position was determined using postoperative clinical imaging. The study involved 10 adult CI recipients. In those with good low-frequency hearing, an increase in signal amplitude was observed, with the highest amplitudes closest to the stimulation frequency generators, and no phase change was observed. Conversely, patients with flat hearing loss exhibited a second peak with an opposite phase in the medial area of the cochlea. This study is the first to suggest that the pattern of the preoperative audiogram may influence the ECochG outcomes measured intraoperatively. Specifically, the ECochG responses during insertion appeared to behave as expected with good low-frequency hearing, while with flat hearing loss there appear to be further effects. These findings indicate that this approach can provide valuable information for the interpretation of intracochlearly recorded ECochG signals.

Does Intraoperative Extracochlear Electrocochleography Correlate With Postoperative Audiometric Hearing Thresholds in Cochlear Implant Surgery? A Retrospective Analysis of Cochlear Monitoring

In recent years, tools for early detection of irreversible trauma to the basilar membrane during hearing preservation cochlear implant (CI) surgery were established in several clinics. A link with the degree of postoperative hearing preservation in patients was investigated, but patient populations were usually small. Therefore, this study's aim was to analyze data from intraoperative extracochlear electrocochleography (ECochG) recordings for a larger group.During hearing preservation CI surgery, extracochlear recordings were made before, during, and after CI electrode insertion using a cotton wick electrode placed at the promontory. Before and after insertion, amplitudes and stimulus response thresholds were recorded at 250, 500, and 1000 Hz. During insertion, response amplitudes were recorded at one frequency and one stimulus level. Data from 121 patient ears were analyzed.The key benefit of extracochlear recordings is that they can be performed before, during, and after CI electrode insertion. However, extracochlear ECochG threshold changes before and after CI insertion were relatively small and did not independently correlate well with hearing preservation, although at 250 Hz they added some significant information. Some tendencies-although no significant relationships-were detected between amplitude behavior and hearing preservation. Rising amplitudes seem favorable and falling amplitudes disadvantageous, but constant amplitudes do not appear to allow stringent predictions.Extracochlear ECochG measurements seem to only partially realize expected benefits. The questions now are: do gains justify the effort, and do other procedures or possible combinations lead to greater benefits for patients?