Electrocochleography as an Objective Measure of the Hearing Threshold

Background: In clinical routine electrocochleography (ECochG) is a well-established tool for evaluation of the inner ear and auditory nerve status.

Objective: With the expansion of cochlear implant (CI) indication criteria towards more residual hearing, implementation of ECochG into the CI system is becoming interesting. In CI users with significant low frequency residual hearing, the inner ear and auditory nerve response to an acoustically presented stimulus can be registered via the implant`s amplifier and transferred telemetrically to the controlling computer.

Methods: In a clinical study on ECochG, 30 subjects with residual hearing to be implanted with an Advanced Bionics CI system have been recruited. During the electrode insertion as well as at the end of the surgery, ECochG shall be recorded from intracochlear electrode contacts. During the first 4 months after implantation ECochG and pure tone thresholds will be measured on each visit. To investigate the relation of the ECochG threshold to hearing thresholds or changes in hearing thresholds, the ECochG results shall be compared to pure tone thresholds.

Results: So far, in 30 subjects ECochG has been registered telemetrically via the implant intra- as well as postoperatively. A good correlation between post-surgical pure tone thresholds and ECochG thresholds could be observed.

Conclusion: In conclusion, postoperative ECochG recordings may serve as an objective indicator of the hearing threshold, e.g. for fitting in case of limited user feedback. Intraoperatively, ECochG might be used for an instantaneous estimation of changes in hearing threshold and with it supporting atraumatic insertion of the electrode array.