Intra- and Postoperative Electrocochleography May Be Predictive of Final Electrode Position and Postoperative Hearing Preservation

Abstract

Introduction: The objectives of the current study were to (1) determine the relationship between electrocochleography (ECochG), measured from the cochlear implant (CI) electrode array during and after implantation, and postoperative audiometric thresholds, (2) determine the relationship between ECochG amplitude and electrode scalar location determined by computerized tomography (CT); and (3) determine whether changes in cochlear microphonic (CM) amplitude during electrode insertion were associated with postoperative hearing.Materials and Methods: Eighteen subjects undergoing CI with an Advanced Bionics Mid-Scala device were prospectively studied. ECochG responses were recorded using the implant coupled to a custom signal recording unit. ECochG amplitude collected intraoperatively concurrent with CI insertion and at activation was compared with audiometric thresholds postoperatively. Sixteen patients also underwent postoperative CT to determine scalar location and the relationship to ECochG measures and residual hearing.Results: Mean low-frequency pure tone average (LFPTA) increased following surgery by an average of 28 dB (range 8–50). Threshold elevation was significantly greater for electrodes with scalar dislocation. No correlation was found between intraoperative ECochG and postoperative behavioral thresholds collapsed across frequency; however, mean differences in thresholds measured by intraoperative ECochG and postoperative audiometry were significantly smaller for electrodes inserted completely within scala tympani (ST) vs. those translocating from ST to scala vestibuli. A significant correlation was observed between postoperative ECochG thresholds and behavioral thresholds obtained at activation.Discussion: Postoperative audiometry currently serves as a marker for intracochlear trauma though thresholds are not obtained until device activation or later. When measured at the same time-point postoperatively, low-frequency ECochG thresholds correlated with behavioral thresholds. Intraoperative ECochG thresholds, however, did not correlate significantly with postoperative behavioral thresholds suggesting that changes in cochlear physiology occur between electrode insertion and activation. ECochG may hold clinical utility providing surgeons with feedback regarding insertion trauma due to scalar translocation, which may be predictive of postoperative hearing preservation.Conclusion: CI insertion trauma is generally not evident until postoperative audiometry when loss of residual hearing is confirmed. ECochG has potential to provide estimates of trauma during insertion as well as reliable information regarding degree of hearing preservation.

Patterns Seen During Electrode Insertion Using Intracochlear Electrocochleography Obtained Directly Through a Cochlear Implant

“…Having identified the patterns witnessed during electrode insertion, the next step is to identify what structural and/or physiological changes may be associated with them. Confirmation of electrode scalar position (i.e., scala tympani versus scala vestibule) using postoperative high-resolution computed tomography is one method of achieving this goal, toward which preliminary work is underway (20). Additionally, there is the need to identify preoperative demographic and audiological factors that may predict these patterns.…”

“…Existing work utilizing intracochlear ECochG has demonstrated its general feasibility and ease of application during CI electrode insertion (5,9,10), its relationship to preoperative hearing levels (19), and its potential to predict postoperative hearing levels and electrode position (20). The purpose of the present study was to characterize the ECochG patterns that the audiologist-surgeon team observes in the “insertion track”—the “live feed” received directly from the CI electrode during its advancement into the cochlea.…”

Electrocochleography in Cochlear Implant Users with Residual Acoustic Hearing: A Systematic Review

“…This bidirectional telemetry system is available for all three major CI devices, as referred to as the Neural Response Telemetry (NRT, Cochlear Ltd.), Neural Response Imaging (NRI, Advanced Bionics), and Auditory Nerve Response Telemetry (ART, MED-EL). The intracochlear ECoG recording via the reverse telemetry system was feasible to offer the real-time feedback of cochlear responses during electrode insertion [ 23 , 24 , 25 , 27 , 41 , 42 , 47 , 48 ]. The prognostic value of intracochlear ECoG obtained in the operating room to assess insertion trauma and predict early postoperative hearing preservation is yet unclear.…”

“…Subjects with preserved CM at the end of insertion had on average 15 dB better low-frequency acoustic hearing compared to subjects with transient or permanent reduction in the CM amplitudes during the insertion process [ 28 ]. However, in subjects who had an average 3 dB drop in CM amplitude during electrode insertion, neither CM amplitude drop from the beginning of insertion to peak amplitude nor drop from peak amplitude to the end of insertion were significantly correlated with postoperative audiometric threshold shift at low frequencies (125–500 Hz) [ 23 ].…”

“…Once hearing preservation became possible for CI users with the development of thinner, flexible electrode arrays and the use of the soft surgical techniques, there were surging interests in using ECoG to measure cochlear function in this expanded CI population. The ECoG has been increasingly used to monitor the status of hearing to mitigate possible intracochlear damage while inserting an electrode and optimize electrode placement during cochlear implant surgery [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Recently, noninvasive recording methods have been developed that allow ECoG responses to be measured from an intracochlear electrode [ 26 , 27 , 28 , 29 , 30 ].…”