Intraoperative cochlear monitoring by use of an extracochlear electrode for the prediction of residual hearing loss

Introduction Obtaining the residual hearing in patients with cochlear implantation and monitoring it as accurately as possible during the operation is a current, central goal in CI implantation. In the present study it was investigated whether a correlation between the course of the intraoperatively carried out ECochG and the change in the threshold of hearing can be established postoperatively and whether it is thus suitable for the intraoperative monitoring of residual hearing.

Method 50 patients with pre-operative residual hearing were enrolled. The lead was carried out by an extracochlear Cotton Wick electrode at the Promontorium. Measurements were performed before, during and after the insertion of the electrode. Tone audiometry was measured preoperatively, on the first postop day and at the time of first fitting.

Results The Cochlear Microphonics were measurable up to 1 μV. In 54% of the cases, a constant or increasing amplitude could be detected during the insertion. 19% of the subjects then had only a hearing loss of 15 dB, 38% lost 15-30 dB. Almost 46% still lost more than 30 dB of their residual hearing. 7 patients (14% of all case) showed a drop in the amplitude curve. In 6% of the cases, no stimulus responses were measurable before or during the insertion.

Conclusion In summary, a decrease in CM amplitude during insertion correlates with a later loss of residual hearing. However, no correlation could be observed between positive or constant progression and retention of residual hearing. The ECochG is thus suitable as a predictive measuring instrument. For further verification, however, further analyses with larger case numbers are necessary.

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Publication History

Article published online:
10 June 2020