Simultaneous Intra- and Extracochlear Electrocochleography During Electrode Insertion

Abstract

Objectives: (1) To correlate simultaneously recorded intra-and extracochlear electrocochleography (ECochG) signals during electrode insertion into the cochlea, (2) to track changes in the ECochG signal during insertion and removal of an electrode, and (3) to correlate the findings with the preoperative residual hearing. We hypothesized that intracochlear ECochG recordings show signal changes not reflected in simultaneous extracochlear ECochG recordings. Design: During cochlear implantation in human cochlear implant recipients, a short, slim, custom-made electrode was inserted and removed in a stepwise manner. At each step, ECochG recordings were simultaneously recorded by an extracochlear electrode near the round window and via the inserted electrode. The acoustic stimulus was a 500 Hz tone burst at 110 to 130 dB SPL. Results: The mean amplitude difference between intra-and extracochlear ongoing ECochG responses was 14 dB (range 9 to 24 dB; n = 10) at the beginning of insertion. Intracochlear ECochG responses were larger in all cases. Extracochlear ECochG responses remained stable while intracochlear recordings showed large variations regarding amplitude and phase during the electrode array insertion. Intracochlear signal changes during insertion were reversible with retraction of the electrode. There were only weak to moderate (rs = 0.006 to 0.4), nonsignificant correlations of residual preoperative hearing with maximum amplitudes and amplitude changes during electrode insertion and removal in intracochlear recordings. Conclusions: Signals in intracochlear ECochG recordings are reliably larger than ECochG signals recorded simultaneously from an extracochlear location. Intracochlear ECochG recordings show reversible amplitude and phase changes during insertion, not reflected in simultaneous extracochlear ECochG recordings. Such changes are most likely due to the movement of the recording electrode in relation to the signal generators. Residual high-frequency hearing is associated with larger ECochG signal amplitudes. Modeling of expected intracochlear ECochG changes during electrode insertions may allow detection of cochlear trauma in the future.

Simultaneous Intra- and Extracochlear Electrocochleography During Cochlear Implantation to Enhance Response Interpretation

“…For the sum curves, this was true in three of the six cases. In a recent study ( Dalbert, Sijgers, et al., 2020 ) in which we investigated simultaneous recordings in atraumatic insertions with a different recording setup for intracochlear recordings, we found intracochlear difference curves to be larger in all cases. Therefore, we assume that intracochlear difference curves should be larger in all simultaneous recordings and that there may have been a problem with the connection between the CI’s most apical electrode and the reference ring electrode in S126, causing the smaller intracochlear responses.…”

“…A better understanding of the generators contributing to the intracochlear ECochG response is needed for distinguishing response decreases related to cochlear damage and response decreases solely resulting from a change in intracochlear recording location during electrode array insertion. Recently, our group conducted a study comparing simultaneous intra- and extracochlear ECochG recordings in atraumatic electrode insertions with a short, custom-made electrode ( Dalbert, Sijgers, et al., 2020 ). The aim was to characterize ECochG signal changes solely occurring due to electrode movements.…”

Objectification of intracochlear electrocochleography using machine learning

“…In addition, there are large inter-individual differences. While some patients show very prominent potentials, in others the signal amplitude is small ( 1 , 3 , 10 , 12 , 52 ). If ECochG is to be used routinely in the operating room and postoperative setting, however, all patients (including those with small signals) must be analyzed.…”

Implications of Phase Changes in Extracochlear Electrocochleographic Recordings During Cochlear Implantation

“…Still, amplitude changes alone seem not to be able to sufficiently detect changes of cochlear function, allowing a reliable prediction of postoperative structure preservation. As a result, phase changes have come into focus and were analyzed in addition to amplitude changes in inE-CochG recordings (37,54).…”