Correlation of Electrophysiological Properties and Hearing Preservation in Cochlear Implant Patients

Abstract

OBJECTIVE: To monitor changes in cochlear function during cochlear implantation using electrocochleography (ECoG) and to correlate changes to postoperative hearing preservation. METHODS: ECoG responses to acoustic stimuli of 250, 500, and 1000 Hz were recorded during cochlear implantation. The recording electrode was placed on the promontory and stabilized to fix the position during cochlear implantation. Baseline recordings were obtained after completion of the posterior tympanotomy. Changes of the ongoing ECoG response at suprathreshold intensities were analyzed after full insertion of the cochlear implant electrode array. Audiometric tests were conducted before and 4 weeks after surgery and correlated with electrophysiological findings. RESULTS: Ninety-five percent (18/19) of cochlear implant subjects had measurable ECoG responses. Under unchanged conditions, recordings showed a high repeatability without significant differences between 2 recordings (p 0.01). Ninety-four percent (17/18) of subjects showed no relevant changes in ECoG recordings after insertion of the cochlear implant electrode array. One subject showed decreases in responses at all frequencies indicative of cochlear trauma. This was associated with a complete hearing loss 4 weeks after surgery compared with mean presurgical low-frequency hearing of 78 dB HL. CONCLUSION: Extracochlear ECoG is a reliable tool to assess cochlear function during cochlear implantation. Moderate threshold shifts could be caused by postoperative mechanisms or minor cochlear trauma. Detectable changes in extracochlear ECoG recordings, indicating gross cochlear trauma, are probably predictive of complete loss of residual acoustic hearing.

Assessment of Cochlear Trauma During Cochlear Implantation Using Electrocochleography and Cone Beam Computed Tomography

“…In cochlear implant recipients, findings thus far have suggested that a decrease of low-frequency ECoG signals at suprathreshold intensities during surgery results in hearing loss of >10 dB or complete hearing loss in a majority of patients (9,10). However, the data showed additionally that changes in low-frequency ECoG recordings during cochlear implantation do not directly translate into postoperative results for hearing threshold levels, and unchanged low-frequency ECoG responses during surgery do not exclude postoperative hearing loss (9)(10)(11)25).…”

“…This definition has been used in multiple studies (27,(30)(31)(32)). An ongoing ECoG response was considered valid if the amplitude exceeded the mean noise floor plus 3 standard deviations (9,10,25,(29)(30)(31)(32). This means that less than 1% false-positive results can be expected.…”

“…The underlying reasons are controversial. Besides cochlear trauma during surgery, postoperative mechanisms seem to cause deterioration of cochlear function (8)(9)(10)(11). Therefore, methods to evaluate and monitor cochlear trauma during cochlear implantation could help to better understand the correlation between cochlear trauma and loss of cochlear function.…”

“…This study was conducted as a follow-up to our first study (10), in which we evaluated changes of lowfrequency ECoG signals at suprathreshold intensities during cochlear implantation. The primary aim was to evaluate if the predictability of postoperative hearing changes by intraoperative ECoG recordings could be increased by the addition of ECoG recordings to highfrequency acoustic stimuli and/or threshold determinations.…”

“…Electrocochleography (ECoG) has shown great potential in this regard and has been conducted in animal studies (19)(20)(21)(22)(23)(24) as well as during and after cochlear implantation in humans (9)(10)(11)(25)(26)(27)(28)(29). To our knowledge, four reports have correlated intraoperative ECoG findings with postoperative hearing preservation rates (9)(10)(11)28). One report showed a close relationship between trauma detected by intraoperative ECoG and postoperative hearing preservation rates (28); whereas the other three suggested limited predictive value of low-frequency ECoG recordings regarding postoperative hearing loss.…”