High-frequency hearing impairment assessed with cochlear microphonics

Digital live imaging of intraoperative electrocochleography during cochlear implantation: the first 50 patients

INTRODUCTION

Real-time visualization of intraoperative electrocochleography (ECochG) potentials via a digital microscope during cochlear implantation can provide direct feedback during electrode insertion. The aim of this prospective, randomized study of 50 patients was to obtain long-term data with a focus on residual hearing preservation and speech understanding.

MATERIAL AND METHODS

Cochlear implantations were performed in 50 patients (26 female, 24 male) with residual hearing using a digital microscope. Patients were randomized into two groups. Intraoperative ECochG potentials were either displayed directly in the surgeon's field of view (picture-in-picture display, PiP) or not directly in the field of view (without picture-in-picture display, without PiP). Residual hearing preservation and speech comprehension were recorded within a 1-year follow-up period, compared between groups (PiP versus without PiP) and to a control group of 26 patients implanted without ECochG.

RESULTS

Mean insertion time was significantly longer in the picture-in-picture group (p = 0.025). Residual hearing preservation after 6 weeks at 250 Hz was significantly better in the picture-in-picture group (p = 0.017). After one year, 76% of patients showed residual hearing in the picture-in-picture group (62% without picture-in-picture technique, p = n.s.). Use of the picture-in-picture technique resulted in better long-term pure tone residual hearing preservation at 250, 500, and 1000 Hz. Speech intelligibility improved by 46% in the picture-in-picture group (38% without picture-in-picture).

DISCUSSION

This study is the first to describe long-term results in a large cohort of cochlear implant patients in whom digital visualization of intraoperative ECochG was used. Our results show that visualization of intraoperative ECochG has a positive effect on residual hearing preservation.

Intracochlear electrocochleography findings in cochlear implant recipients with auditory neuropathy spectrum disorder

OBJECTIVES

This study aimed to compare intracochlear electrocochleography (ECochG) findings in a group of cochlear implant (CI) recipients with auditory neuropathy spectrum disorder (ANSD) with a group of CI recipients with sensorineural hearing loss (SNHL). Auditory outcome and spectral resolution findings were also compared among CI recipients with and without cochlear microphonic (CM) responses.

METHODS

This single-center, prospective cohort study was undertaken at a tertiary referral center. CM responses by the intracochlear ECochG test were recorded in CI recipients at 0.25-2 kHz. Speech, spatial, and hearing quality (SSQ) outcomes and spectral resolution measured with the spectral-temporally modulated ripple test were obtained for each recipient. The study included 62 implanted ears in 46 recipients, of which 59% (n = 27) were male and 41% (n = 19) were female. Twenty-nine ears with ANSD and 33 ears with SNHL were included. The mean age of the participants was 11 years. The results compared the intracochlear ECochG findings of the ANSD group with those of the SNHL group.

RESULTS

Participants were divided into two groups with and without obtainable CM responses. CM responses were obtained in 13 of 29 ears in the ANSD group and 14 of 33 ears in the SNHL group. CM thresholds obtained were better according to behavioral audiometric responses in some frequencies in the ANSD group. No significant difference was found in the auditory outcome and spectral resolution among CI recipients with and without CM responses.

CONCLUSIONS

Intracochlear ECochG has a limited potential clinical value for monitoring ANSD. CM thresholds obtained using ECochG may not reflect behavioral hearing thresholds.

The relationship between round window and ear canal Cochlear microphonic

Hypothesis

Cochlear microphonic recorded at ear canal (CM-EC) can be a substitute for the one recorded at round window (CM-RW).

Background

Almost all clinics do not measure tone-burst evoked CM due to technical difficulty although it can provide more information than click evoked CM. Moreover, clinicians like the CM-EC more than that measured at CM-RW because CM-EC is non-invasive. There is difference between CM-RW and CM-EC, for example, CM-EC is less prominent than CM-RW, therefore, studying tone-burst evoked CM-EC and its relationship with CM-RW are highly significant and can promote the clinical application of CM-EC.

Method

Nine guinea pigs were randomly allocated into three groups, group 1 was not exposed to noise, called normal control. group 2 and group 3 were exposed to the low- (0.5-2 kHz) and high-frequency band-noise (6-8 kHz) at 120 dB SPL for 1 h, respectively. It was difficulty to record low-frequency CM due to severe environmental interruption, in current study the recording technology of tone-burst evoked CM was optimized so that tone-burst evoked CM was measured across full speech frequency (0.5-8 kHz) in the presence of normal hearing and noise induced hearing loss (NIHL).

Results

CM-RW and CM-EC were successfully recorded across speech frequency. Significant reduction in CM amplitude was observed at 0.5 and 2 kHz in group 2, at 6 and 8 kHz in group 3 as compared to group 1, p < .05, indicating that CM amplitude was sensitive to band-noise exposure. Significant correlation between CM-RW and CM-EC was also verified, p < .05.

Conclusion

CM-EC is a useful objective test for evaluation of hearing function; the result of current study supports the clinical application of non-invasive CM-EC.

Can auditory brain stem response accurately reflect the cochlear function?

Auditory brain stem response (ABR) and compound action potential (CAP) recordings have been used in animal research to determine hearing sensitivity. Because of the relative ease of testing, the ABR test has been more commonly used in assessing cochlear lesions than the CAP test. The purpose of this experiment is to examine the difference between these two methods in monitoring the dynamic changes in auditory function after cochlear damage and in detecting asymmetric hearing loss due to unilateral cochlear damage. ABR and CAP were measured in two models of cochlear damage: acoustic trauma induced by exposure to a narrowband noise centered at 4 kHz (2,800-5,600 Hz) at 105 dB sound pressure level for 5 h in chinchillas and unilateral cochlear damage induced by surgical destruction of one cochlea in guinea pigs. Cochlear hair cells were quantified after completing the evoked potential testing. In the noise-damaged model, we found different recovery patterns between ABR and CAP. At 1 day after noise exposure, the ABR and CAP assessment revealed a similar level of threshold shifts. However, at 30 days after noise exposure, ABR thresholds displayed an average of 20-dB recovery, whereas CAP thresholds showed no recovery. Notably, the CAP threshold signifies the actual condition of sensory cell pathogenesis in the cochlea because sensory cell death is known to be irreversible in mammals. After unilateral cochlear damage, we found that both CAP and ABR were affected by cross-hearing when testing the damaged ear with the testing stimuli delivered directly into the canal of the damaged ear. When cross-hearing occurred, ABR testing was not able to reveal the presence of cross-hearing because the ABR waveform generated by cross-stimulation was indistinguishable from that generated by the test ear (damaged ear), should the test ear be intact. However, CAP testing can provide a warning sign, since the typical CAP waveform became an ABR-like waveform when cross-hearing occurred. Our study demonstrates two advantages of the CAP test over the ABR test in assessing cochlear lesions: contributing evidence for the occurrence of cross-hearing when subjects have asymmetric hearing loss and providing a better assessment of the progression of cochlear pathogenesis.NEW & NOTEWORTHY Auditory brain stem response (ABR) is more commonly used to evaluate cochlear lesions than cochlear compound action potential (CAP). In a noise-induced cochlear damage model, we found that the reduced CAP and enhanced ABR caused the threshold difference. In a unilateral cochlear destruction model, a shadow curve of the ABR from the contralateral healthy ear masked the hearing loss in the destroyed ear.

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

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.

Social skills and developmental delay: importance in predicting the auditory and speech outcomes after cochlear implantation in children

CONCLUSION

Preoperative evaluation of social interaction and global development levels using the Vineland Social Maturity Scale (VSMS) and Bayley Scales of Infant Development-2nd edition (BSID-II) may be beneficial in predicting the postoperative outcome in pediatric cochlear implant recipients. In particular, cautious preoperative counseling regarding the poor postoperative prognosis may be necessary in children with low social skills and developmental status.

OBJECTIVE

To determine the clinical benefit of preoperative evaluation of social interaction and global development levels using VSMS and BSID-II in predicting the postoperative outcome in pediatric cochlear implant recipients.

PATIENTS

A total of 65 deaf children who underwent cochlear implantation (CI) were included in this study. Age at the time of implantation ranged from 12 to 76 months. All of the children underwent a comprehensive preimplant psychological assessment by a clinical psychologist. The VSMS and BSID-II were used for evaluating social skills and a child's development preoperatively. A social quotient (SQ) was calculated by using the VSMS for each subject using the following formula: (social age/chronological age) × 100. The auditory perception and speech production abilities were evaluated using the Categories of Auditory Performance (CAP) scale and the Korean version of the Ling's stage (K-Ling), respectively, at 1 year after CI. The associations between the preoperative SQ/developmental levels and the postoperative auditory/speech outcomes were evaluated.

RESULTS

The mean SQ was significantly decreased in the enrolled children (90.6 ± 26.1). The improvement in CAP score at 1 year after CI was correlated with preoperative SQ. The improvements in phonemic and phonologic levels of K-Ling were correlated with preoperative VSMS and BSID-II scores.

Effects of Stimulus Intensity on Low-Frequency Toneburst Cochlear Microphonic Waveforms

This study investigates changes in amplitude and delays in low-frequency toneburst cochlear microphonic (CM) waveforms recorded at the ear canal in response to different stimulus intensities. Ten volunteers aged 20-30 were recruited. Low-frequency CM waveforms at 500 Hz in response to a 14-ms toneburst were recorded from an ear canal electrode using electrocochleography techniques. The data was statistically analyzed in order to confirm whether the differences were significant in the effects of stimulus intensity on the amplitudes and delays of the low-frequency CM waveforms. Electromagnetic interference artifacts can jeopardize CM measurements but such artifacts can be avoided. The CM waveforms can be recorded at the ear canal in response to a toneburst which is longer than that used in ABR measurements. The CM waveforms thus recorded are robust, and the amplitude of CM waveforms is intensity-dependent. In contrast, the delay of CM waveforms is intensity-independent, which is different from neural responses as their delay or latency is intensity-dependent. These findings may be useful for development of the application of CM measurement as a supplementary approach to otoacoustic emission (OAE) measurement in the clinic which is severely affected by background acoustic noise. The development of the application in the assessment of low-frequency cochlear function may become possible if a further series of studies can verify the feasibility, but it is not meant to be a substitute for audiometry or OAE measurements. The measurement of detection threshold of CM waveform responses using growth function approach may become possible in the clinic. The intensity-independent nature of CMs with regards to delay measurements may also become an impacting factor for differential diagnoses and for designing new research studies.