Insight Obtained Through Use of ECochG During and After Electrode Array Insertion

Electrode array insertion is essentially a blind process for the surgeon. By recording electrocochleography (ECochG) during insertion it may be possible to adjust insertion to minimize trauma to the cochlea. Recording after insertion may help establish electrode scala location.

Intra-and post-operative EcochG recordings were made for 20 adult Advanced Bionics recipients. All had at least one pre-operative threshold of or better than 80 dBHL. A 50 ms, 500 Hz acoustic tone burst stimulus was used intra-operatively, with 125, 250 and 500 Hz tones used post-operatively. Subtraction of recordings made for alternate phase stimulation extracted the cochlear microphonic (CM) signal. The time course of CM during insertion was compared to the surgical report. An extrapolated CM threshold was estimated.

ECochG could be recorded in all cases for at least one stimulus frequency. Average electrode insertion time was approximately 30 seconds. A significant correlation was found between ECochG and behavioral estimates of low-frequency hearing threshold (R^2 = 0.71). Changes in CM amplitude during electrode array insertion were in line with surgical report and video review. Correlations between ECochG and post-implant hearing thresholds are currently being accumulated.

ECochG recording has been demonstrated via the standard Advanced Bionics CI hardware. Recording speed increased with insertion depth and was fast enough to give real time surgical feedback. Existing data show a reasonable correlation between CM predicted and behavioral estimates of low-frequency hearing thresholds. These data suggest that ECochG provides a means of assessing and maintaining cochlear health.