Intraoperative Observational Real-time Electrocochleography as a Predictor of Hearing Loss After Cochlear Implantation: 3 and 12 Month Outcomes

Abstract

Objective: A decrease in intracochlear electrocochleographic (ECochG) amplitude during cochlear implantation has been associated with poorer postoperative hearing preservation in several short-term studies. Here, we relate the stability of ECochG during surgery to hearing preservation at 3- and 12-months.

Methods: Patients with hearing ≤80-dB HL at 500 Hz were implanted with a slim-straight electrode array. ECochG responses to short, high-intensity, 500-Hz pure tones of alternating polarity were recorded continuously from the apical-most electrode during implantation. No feedback was provided to the surgeon. ECochG amplitude was derived from the difference response, and implantations classified by the presence ("ECochG drop") or absence ("no drop") of a ≥30% reduction in ECochG amplitude during insertion. Residual hearing (relative and absolute) was reported against the ECochG class.

Results: ECochG was recorded from 109 patients. Of these, interpretable ECochG signals were recorded from 95. Sixty-six of 95 patients had an ECochG drop during implantation. Patients with an ECochG drop had poorer preoperative hearing above 1000 Hz. Hearing preservation (in decibels, relative to preoperative levels and functionally) was significantly poorer at 250-, 500-, and 1000-Hz at 3 months in patients exhibiting an ECochG drop. Twelve-month outcomes were available from 85 patients, with significantly poorer functional hearing, and greater relative and absolute hearing loss from 250 to 1000 Hz, when an ECochG drop had been encountered.

Conclusion: Patients exhibiting ECochG drops during implantation had significantly poorer hearing preservation 12 months later. These observational outcomes support the future development of surgical interventions responsive to real-time intracochlear ECochG. Early intervention to an ECochG drop could potentially lead to prolonged improvements in hearing preservation.

FIG. 1

In the upper panels, ECochG amplitude growth is plotted over a routine cochlear implantation (A) and three examples of ECochG drops (B–D) are presented. The amplitude of “DIF” signal (the difference between responses to rarefaction and condensation 500 Hz tone pips) is a plotted against time from the beginning of the electrode insertion. The lower three panels show the ECochG traces at the times (a, b, c) indicated on the upper panel. ECochG indicates electrocochleographic.

FIG. 2

Preoperative audiometric thresholds. The light gray (left-hand) of each box plot denotes thresholds from patients in whom an ECochG drop was not observed. The black (right-hand) boxes denote data from patients with ECochG drops.

FIG. 3

A to E, Preoperative plotted against 3-month postoperative audiometric thresholds. Data at each frequency is plotted on different rows. Red symbols are from patients who did not experience an ECochG drop, while black symbols are from patients who do exhibit a drop. The right column presents the relative hearing loss (%) at each frequency. These boxplots present median (red line), the interquartile range, with whiskers reflecting the range. Outliers are presented as red crosses. Improved hearing will have a negative value.

FIG. 4

Preoperative plotted against 12-month audiometric thresholds, in the same format as Figure 3.

FIG. 5

Hearing loss between 3 and 12 months after surgery, for those patients in whom audiometric thresholds could still be measured at 3 months.