Noise-induced hearing loss in the contralateral ear during otologic and neurotologic surgeries.

OBJECTIVE: Noise-induced hearing loss in the non-surgical ear during otologic/neurotologic surgery has not been well studied. The purpose of this study was to evaluate changes in hearing that may occur in the contralateral (i.e., non-surgical) ear after various otologic/neurotologic surgeries due to noise generated by drills. We hypothesized that otologic/neurotologic surgeries, longer in duration, would suggest longer drilling times and result in decreased hearing in the contralateral ear as evidenced by a change post-operative pure tone air conduction thresholds when compared to pre-operative thresholds. METHODS: A retrospective chart review at a tertiary referral center. Adult patients (18-75 years old) who underwent otologic/neurotologic surgeries from May 1, 2016 through May 1, 2021 were considered for inclusion. Surgeries included vestibular schwannoma resection (translabyrinthine, middle cranial fossa, or retrosigmoid approaches), endolymphatic sac/shunt and labyrinthectomy for Meniere's disease, and tympanomastoid surgery for middle ear pathology (e.g., cholesteatoma). Patient characteristics obtained through record review included age, sex, surgical procedure, pre-operative and post-operative audiometric thresholds and word recognition scores (WRS) for the contralateral ear, and duration of surgery. RESULTS: No significant differences were observed for change in audiometric thresholds in the contralateral ear for any surgery when considering individual frequencies. Additionally, no significant change in WRS was observed for any surgical approach. CONCLUSIONS: The risk of hearing loss in the non-surgical ear during various otologic/neurotologic surgeries appears to be minimal when measured via routine clinical tests.

Post-operative evaluation of computed tomography imaging following cochlear implantation.

PURPOSE: This study utilized an automated segmentation algorithm to assess the cochlear implant electrode array within the cochlea and investigate its impact on audiologic outcomes as measured by post-operative speech perception scores. Furthermore, manual evaluations of electrode placement were compared to automatic segmentation methods to determine their accuracy in predicting post-operative audiologic outcomes. MATERIALS AND METHODS: This retrospective chart review was conducted at a tertiary care referral center involving adult post-lingually deafened cochlear implant recipients implanted from 2015 to 2019. Patients with appropriate postoperative imaging and speech testing were included. Patients were excluded if non-English speaking, had a cognitive deficit, or a labyrinthine malformation. Automated and manual methods were used to analyze computed tomography (CT) scans and correlate the findings with post-operative speech perception scores and detection of electrode translocation. RESULTS: Among the 47 patients who met inclusion criteria, 15 had electrode translocations confirmed by automatic segmentation methods. Controlling for CI usage and pre-operative AzBio scores, patients with translocation exhibited significantly lower consonant-nucleus consonant (CNC) and AzBio scores at 6-months post-implantation compared to patients with ST insertions. Moreover, the number of translocated electrode contacts was significantly associated with post-operative CNC scores. Manual evaluations of electrode location were predictive but less sensitive to electrode translocations when compared with automated 3D segmentation. CONCLUSIONS: Placement of CI electrode contacts within ST without translocation into SV, leads to improved audiologic outcomes. Manual assessment of electrode placement via temporal bone CT, without 3D reconstruction, provides a less sensitive method to determine electrode placement than automated methods. LEVEL OF EVIDENCE: Level 4. LAY SUMMARY: This study investigated the impact of electrode placement on speech outcomes for cochlear implant recipients. Using advanced imaging techniques, the researchers compared automated and manual methods for evaluating electrode position and examined the relationship between electrode translocation and audiologic outcomes. The findings revealed that proper placement within the cochlea without translocation into inappropriate compartments inside the cochlea improves speech understanding. Manual evaluations were somewhat accurate but less sensitive in detecting translocations compared to automated methods, which offer more precise predictions of patient outcomes. These results contribute to our understanding of factors influencing cochlear implant success and highlight the importance of optimizing electrode placement for improved speech outcomes.

Lack of neural contributions to the summating potential in humans with Meniere's disease.

Objective: To investigate the electrophysiology of the cochlear summating potential (SP) in patients with Meniere's disease (MD). Although long considered a purely hair cell potential, recent studies show a neural contribution to the SP. Patients with MD have an enhanced SP compared to those without the disease. Consequently, this study was to determine if the enhancement of the SP was in whole or part due to neural dysfunction. Design: Study participants included 41 adults with MD and 53 subjects with auditory neuropathy spectrum disorder (ANSD), undergoing surgery where the round window was accessible. ANSD is a condition with known neural dysfunction, and thus represents a control group for the study. The ANSD subjects and 17 of the MD subjects were undergoing cochlear implantation (CI) surgery; the remaining MD subjects were undergoing either endolymphatic sac decompression or labyrinthectomy to alleviate the symptoms of MD. Electrocochleography was recorded from the round window using high intensity (90 dB nHL) tone bursts. The SP and compound action potential (CAP) were measured to high frequencies (> = 2 kHz) and the SP, cochlear microphonic (CM) and auditory nerve neurophonic (ANN) to low frequencies. Linear mixed models were used to assess differences between MD and ANSD subjects. Results: Across frequencies, the MD subjects had smaller alternating current (AC) response than the ANSD subjects (F = 31.61,534, p < 0.001), but the SP magnitudes were larger (F = 94.31,534, p < 0.001). For frequencies less than 4 kHz the SP magnitude in the MD group was significantly correlated with the magnitude of the CM (p's < 0.001) but not in the ANSD group (p's > 0.05). Finally, the relative proportions of both ANN and CAP were greater in MD compared to ANSD subjects. The shapes of the waveforms in the MD subjects showed the presence of multiple components contributing to the SP, including outer and inner hair cells and neural activity. Conclusion: The results support the view that the increased negative polarity SP in MD subjects is due to a change in the operating point of hair cells rather than a loss of neural contribution. The steady-state SP to tones in human subjects is a mixture of different sources with different polarities.

Characterizing Electrophysiological Response Properties of the Peripheral Auditory System Evoked by Phonemes in Normal and Hearing Impaired Ears.

OBJECTIVE: This study aimed to characterize time and spectral domain characteristics of the phoneme-evoked electrocochleography (ECochG) response and explore potential associations between the ECochG spectral content, word recognition scores (WRSs), residual hearing, and aging in normal and hearing-impaired listeners. DESIGN: This was a prospective study with 25 adult participants. All participants underwent intraoperative ECochG testing and responses were recorded from the round window niche. Participants were divided into two groups based on their preoperative pure tone average: normal/mild sensorineural hearing loss and moderate/moderately-severe sensorineural hearing loss. Target stimuli were a 40 ms /da/ and an 80 ms /ba/ presented in alternating polarity (rarefaction/condensation). Waveform response patterns were analyzed including amplitude, latency, and spectra. Structural similarity index measure (SSIM) was used to determine similarity between the stimulus spectrum and that of the ECochG differential waveform. Correlation analyses were carried out among pure tone average, SSIM, age, and WRS. RESULTS: ECochG alternating waveform morphology evoked by the /da/ stimulus consisted of five prominent peaks labeled N 1 -N 5 . Its spectrum was dominated by the fundamental (F 0 ) frequency. The ECochG alternating response evoked by /ba/ consisted of nine prominent peaks labeled N 1 -N 9 and was also dominated by F 0 . Amplitudes and latencies were not statistically different between groups for both stimuli. Significant positive correlations were found between SSIM and WRS for responses evoked by /da/ (r = 0.56) and responses evoked by /ba/ (r = 0.67). High frequency pure tone average and the /ba/ SSIM were found to have a significant negative correlation (r = -0.58). CONCLUSIONS: Speech-like stimuli have become increasingly utilized in the assessment of auditory function. Here, we provided the groundwork for understanding how commonly employed syllable stimuli are encoded by the peripheral auditory system in regard to temporal and spectral characteristics. Expanding this work to include measurements of central auditory processing in conjunction with cochlear physiology is warranted to further understand the relationship between peripheral and central encoding of speech-like stimuli.

Intraoperative Electrocochleography in Subjects Affected by Vestibular Schwannoma and Ménière's Disease: Comparison of Results.

OBJECTIVES: Histologic reports of temporal bones of ears with vestibular schwannomas (VSs) have indicated findings of endolymphatic hydrops (ELH) in some cases. The main goal of this investigation was to test ears with VSs to determine if they exhibit electrophysiological characteristics similar to those of ears expected to experience ELH. DESIGN: Fifty-three subjects with surgically confirmed VS aged ≥18 and with normal middle ear status were included in this study. In addition, a second group of adult subjects (n = 24) undergoing labyrinthectomy (n = 6) or endolymphatic sac decompression and shunt (ELS) placement (n = 18) for poorly controlled vestibular symptoms associated with Meniere's disease (MD) participated in this research. Intraoperative electrocochleography (ECochG) from the round window was performed using tone burst stimuli. Audiometric testing and word recognition scores (WRS) were performed preoperatively. ECochG amplitudes, cochlear microphonic/auditory nerve neurophonic (ANN) in the form of the "ongoing" response and summation potential, were analyzed and compared between the two groups of subjects. In addition, to evaluate any effect of auditory nerve function, the auditory nerve score was calculated for each subject. Pure-tone averages were obtained using the average air conduction thresholds at 0.5, 1, and 2 kHz while WRS was assessed using Northwestern University Auditory Test No. 6 word lists. RESULTS: In the VS group the average pure-tone averages and WRS were 59.6 dB HL and 44.8%, respectively, while in the MD group they were 52.3 dB HL and 73.8%. ECochG findings in both groups revealed a reduced trend in amplitude of the ongoing response with increased stimulus frequency. The summation potential amplitudes of subjects with VS were found to be less negative than the MD subjects for nearly all test frequencies. Finally, the VS group exhibited poorer amounts of auditory nerve function compared to the MD group. CONCLUSIONS: The current findings suggest cochlear pathology (e.g., hair cell loss) in both groups but do not support the hypothesis that VSs cause ELH.

Electrocochleography Observations in a Series of Cochlear Implant Electrode Tip Fold-Overs.

OBJECTIVE: Tip fold-over is a rare but serious complication of cochlear implant (CI) surgery. The purpose of this study was to present intraoperative electrocochleography (ECochG) observations in a series of CI electrode tip fold-overs. PATIENTS: Five pediatric subjects undergoing CI surgery through a round window (RW) approach with a perimodiolar electrode array, who were diagnosed with either auditory neuropathy spectrum disorder or enlarged vestibular aqueduct. INTERVENTIONS: Intraoperative RW ECochG during CI surgery: tone burst stimuli were presented from 95 to 110 dB SPL. MAIN OUTCOME MEASURES: Magnitude and phase characteristics of ECochG responses obtained intraoperatively before and immediately after electrode insertion were examined for patients with and without tip fold-over. RESULTS: Three subjects presented with tip fold-over and two formed the control group. Among fold-over cases, one participant exhibited an inversion in the starting phase of the cochlear microphonic response and a decrease in spectral magnitude from pre- to postinsertion. Both subjects who did not exhibit a change in phase had an increase in the ECochG-total response (ECochG-TR) magnitude. No case in the control group exhibited a change in starting phase. In regard to the ECochG-TR, all controls showed a decrease in the magnitude. CONCLUSIONS: Despite the small number of patients, heterogeneous ECochG response patterns were observed within the fold-over group. Though these results are not conclusive, they can serve as a framework to begin to understand ECochG's utility in detecting intraoperative tip fold-over.

Intraoperative Electrocochleography of Posterior Fossa Tumors Producing Menière's Syndrome.

OBJECTIVES: Intraoperative electrocochleography (ECochG) has provided insight regarding inner ear pathophysiology during neurotologic procedures. In this study, intraoperative ECochG findings are reported in patients who presented with episodic aural and vestibular symptoms during resection of posterior fossa neoplasms. PATIENTS: Three patients with episodic vertigo who underwent resection of posterior fossa tumors. INTERVENTION: Intraoperative ECochG was performed before and after tumor resection with the active electrode at the round window. Acoustic stimuli consisted of click and tone bursts presented in alternating polarity. MAIN OUTCOME MEASURE: ECochG responses including summation potential (SP), action potential (AP), and SP:AP ratio values to evaluate for endolymphatic hydrops. RESULTS: All subjects presented with asymmetric sensorineural hearing loss (SNHL), episodic vertigo, and tinnitus. Subject 1 was a 63-year-old woman who underwent left translabyrinthine excision of an endolymphatic sac (ELS) tumor and demonstrated no measurable responses until fenestration of the lateral semicircular canal, suggesting severe hydrops relieved by labyrinthotomy. Subject 2 was a 44-year-old woman who underwent right ELS tumor resection and exhibited an elevated SP:AP ratio. Subject 3 was a 55-year-old woman who underwent right retrolabyrinthine resection of a meningioma and exhibited robust responses without hydrops. CONCLUSIONS: Endolymphatic hydrops secondary to mechanical obstruction by a posterior fossa neoplasm may be demonstrated using intraoperative ECochG. Immediate improvement of hydrops may not be demonstrated after tumor resection.

Enlarged vestibular aqueduct: Intraoperative electrocochleography findings during cochlear implantation.

Enlarged vestibular aqueduct (EVA) is the most frequent inner ear abnormality found on computed tomography in children with sensorineural hearing loss. The effects EVA abnormalities have on electrocochleography (ECochG) are unknown. Positive deflections in summation potential evoked by tone bursts were observed in 3/5 subjects, while a large negative deflection, similar to endolymphatic hydrops (EH), was observed for 2/5 subjects. The presence of an enlarged summation potential, with and without a compound action potential, was observed in response to a broadband click stimulus. Results suggest likely effects of a third window on ECochG responses and presence of EH in EVA.

Electrocochleography and Cochlear Implantation: A Systematic Review.

OBJECTIVE: Given the heterogeneity of papers about electrocochleography (ECochG) and cochlear implantation (CI) and the absence of a systematic review in the current literature, the aim of this work was to analyze the uses of ECochG in the different stages of CI. DATA SOURCES: A search of PubMed from inception to December 8, 2019, with cross-references, was executed. Keywords were: "Cochlear Implant" OR "Cochlear Implantation" AND "Electrocochleography" OR "ECochG." The main eligibility criteria were English-language articles, investigating the use of ECochG in the different phases of CI. STUDY SELECTION: Literature reviews, editorials, case reports, conference papers were excluded, as were papers in which ECochG was just sporadically executed. DATA EXTRACTION: The quality of the included studies was assessed using "The Strengthening the Reporting of Observational Studies in Epidemiology" (STROBE) Statement. DATA SYNTHESIS: A total of 95 articles were identified and 60 papers were included. The included articles covered a timeframe from 2003 to 2019. Of the 60 papers, 46 were human studies, 12 animal studies, and two involved more data sets. Eleven related to the diagnostic phase, 43 described intraoperative monitoring, and 10 were regarding follow-up testing. Hearing preservation was the most discussed topic with 25 included articles. CONCLUSIONS AND RELEVANCE: ECochG measurements appeared to be useful in many aspects of CI, such as hearing preservation. Our review is the first that shows the evolution of the technique and how much has been achieved from the earliest experiments to the most recent signal process refinements and device implementation in CI.

Utilizing Electrocochleography as a Microphone for Fully Implantable Cochlear Implants.

Current cochlear implants (CIs) are semi-implantable devices with an externally worn sound processor that hosts the microphone and sound processor. A fully implantable device, however, would ultimately be desirable as it would be of great benefit to recipients. While some prototypes have been designed and used in a few select cases, one main stumbling block is the sound input. Specifically, subdermal implantable microphone technology has been poised with physiologic issues such as sound distortion and signal attenuation under the skin. Here we propose an alternative method that utilizes a physiologic response composed of an electrical field generated by the sensory cells of the inner ear to serve as a sound source microphone for fully implantable hearing technology such as CIs. Electrophysiological results obtained from 14 participants (adult and pediatric) document the feasibility of capturing speech properties within the electrocochleography (ECochG) response. Degradation of formant properties of the stimuli /da/ and /ba/ are evaluated across various degrees of hearing loss. Preliminary results suggest proof-of-concept of using the ECochG response as a microphone is feasible to capture vital properties of speech. However, further signal processing refinement is needed in addition to utilization of an intracochlear recording location to likely improve signal fidelity.

Electrocochleography During Translabyrinthine Approach for Vestibular Schwannoma Removal.

HYPOTHESIS: Intraoperative electrocochleography (ECochG) can differentiate hair cell and neural dysfunction caused by a vestibular schwannoma (VS) and help define the site of lesion as peripheral or central to the spiral ganglion. BACKGROUND: Hearing loss in patients with a VS can be caused by both sensory (cochlear) and neural dysfunction. METHODS: Round-window ECochG using low and high-frequency tone bursts was performed in 49 subjects with a VS. Responses were analyzed for magnitude, spectrum, and shape of the time waveform. Components examined included the cochlear microphonic, auditory nerve neurophonic, compound action potential (CAP), and summating potential (SP). RESULTS: Variability in the summed response magnitudes across frequency, or "total response" (ECochG-TR), varied from 0.1 to 100 µV. Responses were larger for lower frequencies. Subjective estimates revealed a wide range of neural contributions from the auditory nerve neurophonic to low frequencies and the CAP to high frequencies. Cases with larger CAPs had smaller SPs. The correlation of ECochG-TR, with word recognition score (WRS), was moderate (r = 0.67), as well as the correlation between pure-tone averages and ECochG (r = 0.63). The cochlea remained functional in two cases of sudden sensorineural hearing loss with 0% WRS. CONCLUSION: Reduced ECochG-TR and neural activity in many cases indicates both sensory and neural deficits. Smaller SPs when CAPs are present indicate a neural contribution to the SP. Good cochlear function with 0% WRS, and cases of sudden sensorineural hearing loss with retained cochlear function, indicate retrocochlear effects, typically proximal to the spiral ganglion cells.

Intraoperative Monitoring of Auditory Function During Lateral Skull Base Surgery.

OBJECTIVE: We present a unique case of a patient with a jugular foramen tumor with serviceable hearing. This study discusses the audiometric results and intraoperative electrocochleographic (ECochG) findings recorded during tumor removal to illustrate the potential utility of this technique in skull base surgery. PATIENTS: A 22-year-old female patient presented with a jugular foramen schwannoma and associated symptoms of right-sided otalgia, mild hearing loss, and blurry vision. INTERVENTIONS: Intraoperative ECochG responses during an infratemporal fossa approach: click and tone burst (1, 2, 4 kHz) stimuli were used and presented at 90 dB nHL. MAIN OUTCOME MEASURES: Intraoperative ECochG testing using frequency-specific tone bursts and clicks before and after tumor resection. RESULTS: The compound action potential magnitudes, cochlear microphonic, and summation potential were recorded pre- and post-tumor removal. For statistical analysis, a paired t test with significance set at p < 0.05 was used. The compound action potential magnitudes increased at all test frequencies (p < 0.01) while the summation potential and cochlear microphonic remained relatively stable (p > 0.05). Audiometric testing demonstrated an improvement of the preoperative mild right-sided hearing loss after tumor resection (pure-tone average for 0.5, 1, 2, and 4 kHz of 30 dB HL preoperation and 7.5 dB HL after tumor resection). CONCLUSIONS: Intraoperative ECochG may allow for real-time monitoring during complex skull base surgery.

Intraoperative Electrocochleography in Patients With Menière's Disease Undergoing Endolymphatic Sac Decompression and Shunt Surgery.

HYPOTHESIS: Objective physiologic changes measured using electrocochleography at the round window (ECOG) are observable during endolymphatic sac decompression and shunt surgery (ELS). BACKGROUND: Limited effective treatment options are available to patients with Menière's disease (MD) who have failed conservative management, experience persistent vertigo symptoms, and have substantial residual hearing. ELS is a feasible therapeutic option for these patients. However, the efficacy of this procedure has been questioned, and objective measures assessing inner ear physiologic alterations are lacking. METHODS: ECOG was measured in patients with MD undergoing ELS. Stimuli consisted of tone bursts (250, 500, 1000, 2000, 4000 Hz) and 100 µs broadband clicks at various intensities (60-90 dB nHL). Cochlear microphonic (CM), summation potential (SP), compound action potential (AP), SP:AP ratio, and CM harmonic distortions were measured. RESULTS: ECOG was completed in 18 patients. The mean SP magnitude at 500 Hz changed significantly from -7.1 µV before to -5.1 µV after ELS (p < 0.05). However, the mean SP:AP ratio in those tested (n = 13) did not significantly change after ELS. CM harmonic magnitudes remained unchanged from pre- to post-ELS (n = 12) across all frequencies. CONCLUSION: ECOG allows detection of acute electrophysiological changes in the cochlea. However, our results indicate only small objective changes in the low-frequency SP magnitude (500 Hz) immediately after ELS, but not in other frequencies or measures tested (CM, SP:AP, CM harmonic distortions). These results suggest minimal electrophysiological changes occur in the cochlea as a result of ELS.

Vestibular perception and the vestibulo-ocular reflex in young and older adults.

OBJECTIVES: Quantification of the perceptual thresholds to vestibular stimuli may offer valuable complementary information to that provided by measures of the vestibulo-ocular reflex (VOR). Perceptual thresholds could be particularly important in evaluating some subjects, such as the elderly, who might have a greater potential of central as well as peripheral vestibular dysfunction. The authors hypothesized that perceptual detection and discrimination thresholds would worsen with aging, and that there would be a poor relation between thresholds and traditional measures of the angular VOR represented by gain and phase on rotational chair testing. DESIGN: The authors compared the detection and discrimination thresholds of 19 younger and 16 older adults in response to earth-vertical, 0.5 Hz rotations. Perceptual results of the older subjects were then compared with the gain and phase of their VOR in response to earth-vertical rotations over the frequency range from 0.025 to 0.5 Hz. RESULTS: Detection thresholds were found to be 0.69 ± 0.29 degree/sec (mean ± standard deviation) for the younger participants and 0.81 ± 0.42 degree/sec for older participants. Discrimination thresholds in younger and older adults were 4.83 ± 1.80 degree/sec and 4.33 ± 1.57 degree/sec, respectively. There was no difference in either measure between age groups. Perceptual thresholds were independent of the gain and phase of the VOR. CONCLUSIONS: These results indicate that there is no inevitable loss of vestibular perception with aging. Elevated thresholds among the elderly are therefore suggestive of pathology rather than normal consequences of aging. Furthermore, perceptual thresholds offer additional insight, beyond that supplied by the VOR alone, into vestibular function.

Temporal binding of auditory and rotational stimuli.

Integration of cues from multiple sensory channels improves our ability to sense and respond to stimuli. Cues arising from a single event may arrive at the brain asynchronously, requiring them to be "bound" in time. The perceptual asynchrony between vestibular and auditory stimuli has been reported to be several times greater than other stimulus pairs. However, these data were collected using electrically evoked vestibular stimuli, which may not provide similar results to those obtained using actual head rotations. Here, we tested whether auditory stimuli and vestibular stimuli consisting of physiologically relevant mechanical rotations are perceived with asynchronies consistent with other sensory systems. We rotated 14 normal subjects about the earth-vertical axis over a raised-cosine trajectory (0.5 Hz, peak velocity 10 deg/s) while isolated from external noise and light. This trajectory minimized any input from extravestibular sources such as proprioception. An 800-Hz, 10-ms auditory tone was presented at stimulus onset asynchronies ranging from 200 ms before to 700 ms after the onset of motion. After each trial, subjects reported whether the stimuli were "simultaneous" or "not simultaneous." The experiment was repeated, with subjects reporting whether the tone or rotation came first. After correction for the time the rotational stimulus took to reach vestibular perceptual threshold, asynchronies spanned from -41 ms (auditory stimulus leading vestibular) to 91 ms (vestibular stimulus leading auditory). These values are significantly lower than those previously reported for stimulus pairs involving electrically evoked vestibular stimuli and are more consistent with timing relationships between pairs of non-vestibular stimuli.