Hearing Preservation After Cochlear Reimplantation Using Electrocochleography: A Case Report

INTRODUCTION:

As more patients are undergoing cochlear implantation (CI), the incidence of reimplantation has increased. Prior reports have discussed reimplantation in ~ 5% of CIs for device failure, electrode migration, facial nerve stimulation (FNS), or receiver/stimulator migration.¹ Although the goal of reimplantation is to resolve the underlying issue while preserving or improving CI speech-perception performance, the ideal approach for achieving this goal, particularly for patients with residual hearing, is unclear.

Prior case studies have discussed feasibility of hearing preservation (HP) after reimplantation in the context of lateral wall or short/hybrid electrodes.² In these cases, HP could not be predicted after reimplantation as there was no intraoperative monitoring of cochlear health. A critical question remains whether surgical monitoring with objective intraoperative electrophysiologic measures (ie, electrocochleography [ECochG]) can assist with HP during reimplantation. Here, we describe a patient who was implanted with a slim lateral wall electrode (CI624) and developed severe FNS refractory to electrode reprogramming. She then underwent reimplantation with a perimodiolar electrode (CI612) using real-time ECochG to guide reimplantation for preservation of low-frequency hearing. We report the first case in the literature of successful HP using ECochG during reimplantation. This study was approved by the IRB of Washington University.

CASE REPORT:

A 27-year-old female presented for CI evaluation with a 25-year history of left-sided hearing loss of unknown etiology. Audiometric testing revealed normal hearing sensitivity through 250 Hz with steeply sloping to severe-to-profound hearing loss beginning at 500 Hz. The patient scored a 4% on AzBio in quiet and 10% on consonant-nucleus-consonant (CNC) words in the ear to be implanted. She met criteria for CI and was implanted with the CI624 using a round window (RW) approach. This array is 20 mm in length with 22 electrode contacts, designed for basal support and assists in preservation of the apical portion of the cochlea. Intraoperative electric compound action potentials using neural response telemetry met expected thresholds and abnormal facial nerve activity was not observed.

Audiologic testing 1-month post-implantation was consistent with HP at low frequencies, with 125 Hz and 250 Hz within the range of normal hearing (Figure 1). However, she first noted significant facial stimulation (Kelsall Grade III³) 1 week after activation, which was refractory to changing the programming strategy and stimulation mode, turning off certain electrodes, and reducing C-levels under FNS thresholds. CT was performed which revealed a concerning region for cochlear-facial dehiscence at the basal turn of the cochlea (Figure 2). Because she was unable to use her processor, the decision was made to explant the CI624 and reimplant the CI612 as perimodiolar electrodes generally have a lower incidence of FNS. Preoperatively, intracochlear ECochG potentials were measured from the most apical electrode of the implant using the Cochlear Research Platform Ver 1.1. An ER3-14A (Etymotic) earphone was placed into the external auditory canal, and tone burst stimuli at 0.25, 0.5, 1, and 2 kHz were presented (Table 1). Processing of ECochG total response has previously been described (Figure 3).⁴

Figure 1:

Audiometric testing showing preservation of low-frequency thresholds before explantation of lateral wall electrode (CI624) and three months after reimplantation of the perimodiolar electrode (CI612).

Figure 2:

Cochlear-facial dehiscence in a 27-year-old female patient with facial nerve stimulation after cochlear implantation. (A) Coronal computed tomography (CT) view of the left inner ear showing lack of osseous separation between the labyrinthine facial nerve and cochlea, consistent with cochlear-facial dehiscence. (B) Axial CT view showing an osseous defect between the superolateral aspect of the cochlea and the labyrinthine segment of the facial nerve.

Table 1:

Frequency-specific electrocochleography (ECochG) response prior to explantation of lateral wall electrode (CI624) and after reimplantation of the perimodiolar electrode (CI612). Tone bursts (0.25, 0.5, 1, 2 kHz) were presented to at 108 dB HL for 100 repetitions and alternating polarity waveforms were extracted into MATLAB for fast Fourier transformation. Significant responses, relative to the noise floor, were calculated from the first, second, and third harmonics across all stimulus frequencies to determine the ECochG total response (TR).

	ECochG Response (μV)
	Prior to Explantation	Post-Reimplantation
250 Hz	20.58	23.53
500 Hz	1.47	11.92
1000 Hz	1.76	No response
2000 Hz	0.17	1.36
ECochG Total Response (dB re: 1 μV)	27.60	31.32

Figure 3:

Electrocochleography recording from the most apical electrode after full insertion of the perimodiolar array (CI612). (A) Response to 250 Hz at 108 dB HL. The top panel shows the time series from summation (Sum, blue line) and difference (Diff, orange line) waveforms. The lower panel shows the spectrum of the response. Only the first harmonic was statistically significant for 250 Hz relative to the noise floor. (B) Response (time series and spectrum) to 500 Hz at 108 dB HL. (C) Response to 1000 Hz at 108 dB HL. Prominent compound action potential (CAP) is noted along the summation time series plot.

There was no difficulty with explantation of the CI624 as there was no connective tissue sleeve around the electrode. After explantation, Decadron (10 mg/mL; Somerset Therapeutics, Mendham, NJ) was applied into the RW to serve as a lubricant for reimplantation. Additionally, 10 mg of Decadron was intravenously administered. Continuous intracochlear ECochG recording was used to assist with the reimplantation (Figure 4). As the CI612 was advanced on stylet into the RW, two drops in amplitude occurred during the insertion, suggesting impending trauma. Insertion was paused for 1-2 seconds and the electrode was withdrawn 1 mm to allow recovery of ECochG response and then reinserted. The electrode was inserted up to the second stiffening ring with no resistance. ECochG added 5 minutes to the operative time for conditioning of electrode and baseline response measurements. Intraoperative x-ray confirmed no tip fold-over. Patient was discharged with a Medrol Dosepak.

Figure 4:

Active insertion plot using electrocochleography (ECochG) at a tone burst stimulus of 250 Hz (duration 20 ms, rate 14/sec with alternating polarity, 1 ms rise/fall, 108 dB HL) for the CI612 perimodiolar electrode. A fast Fourier transformation was performed on the continuous signal as measured from the most apical electrode. There was an increase in the ECochG response with no irrecoverable responses throughout the slow insertion that suggested limited trauma throughout the insertion. There were two time points (red arrows) where there was a drop in response, concerning for impending trauma. The surgeon responded to feedback with pausing the insertion and withdrawing the electrode 1 mm to allow for recovery of the ECochG response and then proceeding with insertion.

HP was confirmed postoperatively where low-frequency pure tone average prior to explantation was 35.0 dB HL and 3 months after reimplantation was 36.7 dB HL (Supplementary Figure 1). FNS and otalgia had resolved. As the patient has normal hearing at 125 and 250 Hz, she has decided to not use electro-acoustic stimulation and leaves her ear canal unoccluded for natural acoustic input.

DISCUSSION:

No studies to date have examined the role of reimplantation in patients with FNS refractory to electrode reprogramming or the utility of ECochG to assist with HP during reimplantation. This case study confirms that low-frequency hearing can be preserved using a perimodiolar electrode for reimplantation with the assistance of ECochG for real-time monitoring.

The approach for this patient is unique when compared to previous HP reimplantation reports. Since the patient had a history of severe FNS with the lateral wall array and concern for cochlear-facial nerve dehiscence on imaging, a perimodiolar array was selected for reimplantation due to its low incidence of FNS. This is based on the theory that the intracochlear electrodes of the perimodiolar arrays are half-banded and are closer to and face the modiolus; thus, minimizing the current traveled towards the outer wall of the cochlea.⁵ In retrospect, the CI622 (slim straight electrode) may have been a better choice for the initial surgery as this electrode is half-banded and could be used for HP.

This case study also shows that HP is possible with a standard length perimodiolar array (CI612), which is generally not considered a HP array. Prior studies have used shorter, HP electrodes for initial implantation and then used standard length electrodes for reimplantation after device failure resulting in loss of residual hearing.² One potential explanation for achieving HP may be the utility of active insertion feedback via intracochlear ECochG.

CONCLUSION:

As a result of the increasing incidence of reimplantation, it is imperative to understand the variables that may affect HP and speech outcomes after reimplantation. Intracochlear ECochG may have an important role in minimizing trauma during reimplantation. Examining case studies like this and others discussing reimplantation in the context of HP may provide insight on the best approaches to preserve residual hearing.

Supplementary Material

fS1

Supplementary Figure 1: Audiometric data prior to explantation of CI624 (A) and 3 months after reimplantation of CI612 (B).