Intraoperative cochlear monitoring by use of an extracochlear electrode: correlation between hearing threshold in tone audiogram and intraoperative course of the ECochG

Introduction:

The topic of residual hearing in patients with cochlear implantation plays an increasingly important role in current research approaches.

In the present study, it was investigated whether a correlation between the course of intraoperatively measured ECochG and the change in the threshold of hearing can be detected pre- and postoperatively and whether it is thus suitable for the intraoperative monitoring of residual hearing.

Methods:

The study included patients with pre-operative residual hearing. The derivation was carried out by an extracochlear Cotton Wick electrode placed on the promontorium. Measurements were made before, during and after the insertion of the electrode.

In addition, an evaluation of the pre- and postoperative audio audiograms was performed.

Results:

Initial analyzes show amplitudes up to 1µV. In 50% of the cases a constant amplitude progression is observed intraoperatively (-0.1µV ≤ Δ ≤0.1µV). In 30% of the cases a decrease of the amplitude progression, as well as in 10% an increase, could be observed. In another 10%, no stimulus responses were detected. Compared to the course of the audiometric auditory threshold pre- and postoperatively, in spite of constant intraoperative amplitude progression, a decrease by more than 30 dB was noticed in 60% of the cases. In 20% of the cases a decrease of 15 – 30 dB could be detected, and in 20% a low level drop up to max. 15 dB.

In the case of a decrease in the amplitude, a drop in the threshold between 15 and 30 dB could also be observed.

Conclusions:

In summary, there was an initial correlation between the drop in response during insertion and a later decline in hearing threshold. For validation as a predictive measurement tool for residual hearing, however, further analysis is needed.

Publication History

Publication Date:
23 April 2019 (online)