Multi-Frequency Intraoperative Monitoring of Hearing Preservation during Cochlear Implantation

Abstract

(1) Background: Current indications for cochlear implants (CIs) have expanded to include patients with appreciable low-frequency hearing. However, longitudinal results indicate that only one-third of these recipients retain full hearing preservation. In another words, the remaining two-thirds lose this facility either partially or fully. This points to the need to better understand the impact of cochlear implantation on cochlear integrity. Intracochlear electrocochleography (ECochG) involves the recording of electrical potentials generated in the inner ear in response to acoustic stimuli, and previous studies have shown that these potentials give an indication of residual inner ear function. Aim of the research: The aim is to monitor intracochlear ECochG during CI surgery and gain a better understanding of how the implant impacted inner ear function. A newly developed SPL Chirp was used for stimulation. (2) Methods: Intracochlear ECochG signals were measured in a subject with residual preoperative low-frequency hearing, while an electrode array was introduced into the cochlea and was continued until the round window was sealed. Afterwards, surgical events were reviewed with the surgeon; preoperative and postoperative radiological data and hearing thresholds were also evaluated. (3) Conclusions: Real-time intraoperative monitoring, with multifrequency evaluation and video recording, has the potential to allow surgeons and audiologists to continuously assess cochlear function. ECochG monitoring may be a useful tool during cochlear implantation to gain frequency-specific information on the status of the patient's hearing, assisting surgeons to lower hearing trauma during the operation.

Keywords: cochlear implant; electrocochleography; partial deafness treatment (PDT).

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1

Setup of the intracochlear ECochG measurements. Acoustic simulation is delivered by an insert ear phone; inner ear responses are picked up by the implant electrode and passed to a telemetry and recording system.

Figure 2

Preoperative audiogram (blue) and postoperative audiograms after 1 and 3 months (orange and grey).

Figure 3

Real-time intraoperative ECochG monitoring (μV) during electrode insertion, along with highlighted surgical events from Table 1 (arrows). The main plot shows the amplitudes of each of the harmonics (red: 0.25 kHz; yellow: 0.5 kHz; light green: 1 kHz, dark green: 2 kHz, light blue: 4 kHz). The plot at bottom (red line) depicts the latency of the response. The numbered traces are continuous recordings from the most apical electrode. The top right image depicts the shows the estimated insertion angle of each of the 12 electrodes, up to 490° according to Otoplan v3.1.

Figure 4

Preoperative and postoperative evaluation from Otoplan v.3.1.