We aimed to investigate the clinical features of cochlear nerve deficiency (CND), and in particular, the long-term course of hearing disability and audiogram shapes.
Retrospective observational ...nonrandomized group study.
Academic medical center.
The subjects were 63 children with congenital hearing loss who visited our hospital between 2009 and 2019 and underwent MRI, based on which they were diagnosed with CND. There were 61 cases of unilateral CND and two cases of bilateral CND.
Imaging tests by MRI and CT and audiometric assessments by pure-tone audiometry and distortion product otoacoustic emission were performed.
Among the cases of CND diagnosed by assessing the cochlear nerve on MRI, approximately 20% of the bony cochlear nerve canals that could be assessed on CT were normal. Of the 61 cases diagnosed with unilateral CND, 55 cases had cochlear nerve aplasia (90.2%), and six had cochlear nerve hypoplasia (9.8%), with a mean hearing ability of 92.2 and 94.6 dB HL, respectively. Thus, the majority of cases had severe-to-profound hearing loss. The overall audiometric patterns were 78.7% flat, 9.8% cookie-bite, and 9.8% high-frequency. Six of 61 cases (9.8%) had a distortion product otoacoustic emission (DPOAE) response based on the affected side, and none of the cases lost the response during follow-up.
Herein, we report the largest study on CND and performed CND image and audiometric assessments. Accurately in diagnosing CND requires not only CT but also MRI assessment. Hearing loss is often severe to profound; however, various audiometric patterns have been observed. CND includes a small number of cases that respond to DPOAE, indicating that some CND cases are clinically diagnosed with auditory neuropathy spectrum disorder (ANSD). A sustained DPOAE response might help in differentiating CND from other ANSDs. Children with congenital deafness who have passed the newborn hearing screening by DPOAE should be examined by MRI to rule out CND.
Objective To identify factors predicting performance outcomes following cochlear implantation in patients with cochlear nerve aplasia or hypoplasia. Data Sources Individual patient data extracted ...from published case series and reports. Review Methods The MEDLINE database, Cochrane Library, Embase, Web of Science, and Google Scholar were queried for "cochlear implant" in conjunction with "aplasia" or "hypoplasia" between 1985 and 2015. Eighteen studies were included describing 97 subjects with individual postimplant auditory data. Postimplant performance was categorized as follows: level 1, nonstimulation/minimal detection; level 2, improved detection; level 3, closed-set speech perception; or level 4, open-set speech perception. The subjects achieving speech perception (levels 3 and 4) were descriptively compared with those who did not. Results Subjects with a hypoplastic cochlear nerve on magnetic resonance imaging had higher reported rates of achieving speech perception than those with an aplastic nerve. Subjects with syndromic medical comorbidities had higher reported rates of nonstimulation than nonsyndromic subjects. The data showed that some children with an aplastic cochlear nerve or those with partial electrode insertion could obtain levels of speech discrimination. Reporting of patient characteristics and auditory outcomes was extremely variable across studies. Conclusion As previously shown, cochlear implant in patients with cochlear nerve aplasia or hypoplasia can provide meaningful hearing for select patients. The current study suggests that presence of a cochlear nerve on magnetic resonance imaging and lack of comorbid medical syndrome are associated with better auditory outcomes in such patients. Future efforts to report individual data in a consistent manner may allow better determination of predictive factors.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Common causes of hearing loss in humans - exposure to loud noise or ototoxic drugs and aging - often damage sensory hair cells, reflected as elevated thresholds on the clinical audiogram. Recent ...studies in animal models suggest, however, that well before this overt hearing loss can be seen, a more insidious, but likely more common, process is taking place that permanently interrupts synaptic communication between sensory inner hair cells and subsets of cochlear nerve fibers. The silencing of affected neurons alters auditory information processing, whether accompanied by threshold elevations or not, and is a likely contributor to a variety of perceptual abnormalities, including speech-in-noise difficulties, tinnitus and hyperacusis. Work described here will review structural and functional manifestations of this cochlear synaptopathy and will consider possible mechanisms underlying its appearance and progression in ears with and without traditional ‘hearing loss’ arising from several common causes in humans.
•Noise can cause rapid synaptic loss and slow degeneration of cochlear nerve fibers, even if hair cells survive.•Diffuse cochlear synaptopathy does not raise audiometric or ABR thresholds, but does decrease ABR amplitudes.•Ears exposed to ‘synaptopathic’ noise show exaggerated synaptic and neural losses as they age after exposure.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Recent animal work has suggested that cochlear synapses are more vulnerable than hair cells in both noise-induced and age-related hearing loss. This synaptopathy is invisible in conventional ...histopathological analysis, because cochlear nerve cell bodies in the spiral ganglion survive for years, and synaptic analysis requires special immunostaining or serial-section electron microscopy. Here, we show that the same quadruple-immunostaining protocols that allow synaptic counts, hair cell counts, neuronal counts and differentiation of afferent and efferent fibers in mouse can be applied to human temporal bones, when harvested within 9 h post-mortem and prepared as dissected whole mounts of the sensory epithelium and osseous spiral lamina. Quantitative analysis of five “normal” ears, aged 54–89 yrs, without any history of otologic disease, suggests that cochlear synaptopathy and the degeneration of cochlear nerve peripheral axons, despite a near-normal hair cell population, may be an important component of human presbycusis. Although primary cochlear nerve degeneration is not expected to affect audiometric thresholds, it may be key to problems with hearing in noise that are characteristic of declining hearing abilities in the aging ear.
•Human temporal bones were immunostained and examined by confocal microscopy.•“Normal” ears from 54 to 89 yrs with no history of otologic disease were selected.•Hair cells, synaptic ribbons, cochlear nerve axons and efferent axons were counted.•Results showed cochlear neurodegeneration without hair cell loss in the oldest ears.•Results suggest that primary neural degeneration is important in human presbycusis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Sound-evoked compound action potential (CAP), which captures the synchronous activation of the auditory nerve fibers (ANFs), is commonly used to probe deafness in experimental and clinical settings. ...All ANFs are believed to contribute to CAP threshold and amplitude: low sound pressure levels activate the high-spontaneous rate (SR) fibers, and increasing levels gradually recruit medium- and then low-SR fibers. In this study, we quantitatively analyze the contribution of the ANFs to CAP 6 days after 30-min infusion of ouabain into the round window niche. Anatomic examination showed a progressive ablation of ANFs following increasing concentration of ouabain. CAP amplitude and threshold plotted against loss of ANFs revealed three ANF pools: 1) a highly ouabain-sensitive pool, which does not participate in either CAP threshold or amplitude, 2) a less sensitive pool, which only encoded CAP amplitude, and 3) a ouabain-resistant pool, required for CAP threshold and amplitude. Remarkably, distribution of the three pools was similar to the SR-based ANF distribution (low-, medium-, and high-SR fibers), suggesting that the low-SR fiber loss leaves the CAP unaffected. Single-unit recordings from the auditory nerve confirmed this hypothesis and further showed that it is due to the delayed and broad first spike latency distribution of low-SR fibers. In addition to unraveling the neural mechanisms that encode CAP, our computational simulation of an assembly of guinea pig ANFs generalizes and extends our experimental findings to different species of mammals. Altogether, our data demonstrate that substantial ANF loss can coexist with normal hearing threshold and even unchanged CAP amplitude.
Overexposure to intense sound can cause temporary or permanent hearing loss. Postexposure recovery of threshold sensitivity has been assumed to indicate reversal of damage to delicate mechano-sensory ...and neural structures of the inner ear and no persistent or delayed consequences for auditory function. Here, we show, using cochlear functional assays and confocal imaging of the inner ear in mouse, that acoustic overexposures causing moderate, but completely reversible, threshold elevation leave cochlear sensory cells intact, but cause acute loss of afferent nerve terminals and delayed degeneration of the cochlear nerve. Results suggest that noise-induced damage to the ear has progressive consequences that are considerably more widespread than are revealed by conventional threshold testing. This primary neurodegeneration should add to difficulties hearing in noisy environments, and could contribute to tinnitus, hyperacusis, and other perceptual anomalies commonly associated with inner ear damage.
Objectives/Hypothesis
To identify the imaging characteristics associated with better hearing outcomes found in cochleovestibular nerve (CVN) abnormalities treated with hearing aids and/or cochlear ...implantation (CI).
Study Design
Retrospective review.
Methods
A retrospective review was undertaken of 69 ears with CVN abnormalities seen on magnetic resonance imaging (MRI) treated at a tertiary referral academic center analyzing the clinical features, imaging characteristics, and hearing data. We searched for associations among the hearing and imaging data, hypothesizing that the imaging data was not a good indicator of hearing function.
Results
In univariable analysis of all those who underwent aided testing (hearing aid and CI), health status (P = .016), internal auditory canal (IAC) midpoint diameter (P < .001), and number of nerves in the IAC (P < .001) were predictors of positive hearing outcome. Modiolar abnormalities, cochlear aperture diameter, cochlear malformations, vestibular malformations, and nerves in the cerebellar cistern did not predict hearing outcome (P = .79, .18, .59, .09, .17, respectively). For patients who received CI, health status (P = .018), IAC midpoint (P = .024), and number of nerves in the IAC (P = .038) were significant. When controlling for health status, IAC midpoint diameter (P < .001) and number of nerves in the IAC (P < .001) remained significant. In our cohort, one out of the eight ears (13%) with Birman class 0 or 1 exhibited responses to sound compared to nine out of 13 ears (70%) with Birman class 2–4.
Conclusions
Current imaging modalities cannot accurately depict the status of the cochleovestibular nerve or predict a child's benefit with a CI. Cochlear implantation should be considered in children with abnormal cochleovestibular nerves.
Level of Evidence
3 Laryngoscope, 132:S1–S15, 2022
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Pediatric data regarding treatment via an auditory brainstem implant (ABI) remains sparse. The authors aimed to describe their experience at their institution and to delineate associated demographic ...data, audiometric outcomes, and surgical parameters.
An IRB-approved, retrospective chart review was conducted among the authors' pediatric patients who had undergone auditory brainstem implantation between 2012 and 2021. Demographic information including sex, age, race, coexisting syndrome(s), history of cochlear implant placement, average duration of implant use, and follow-up outcomes were collected. Surgical parameters collected included approach, intraoperative findings, number of electrodes activated, and complications.
A total of 19 pediatric patients had an ABI placed at the authors' institution, with a mean age at surgery of 4.7 years (range 1.5-17.8 years). A total of 17 patients (89.5%) had bilateral cochlear nerve aplasia/dysplasia, 1 (5.3%) had unilateral cochlear nerve aplasia/dysplasia, and 1 (5.3%) had a hypoplastic cochlea with ossification. A total of 11 patients (57.9%) had a history of cochlear implants that were ineffective and required removal. The mean length of implant use was 5.31 years (0.25-10 years). Two patients (10.5%) experienced CSF-related complications requiring further surgical intervention. The most recent audiometric outcomes demonstrated that 15 patients (78.9%) showed improvement in their hearing ability: 5 with sound/speech awareness, 5 able to discriminate among speech and environmental sounds, and 5 able to understand common phrases/conversation without lip reading. Nine patients (47.4%) are in a school for the deaf and 7 (36.8%) are in a mainstream school with support.
The authors' surgical experience with a multidisciplinary team demonstrates that the retrosigmoid approach for ABI placement in children with inner ear pathologies and severe sensorineural hearing loss is a safe and effective treatment modality. Audiometric outcome data showed that nearly 79% of these patients had an improvement in their environmental and speech awareness. Further multicenter collaborations are necessary to improve these outcomes and potentially standardize/enhance electrode placement.
Sensorineural hearing impairment is the most common form of hearing loss, and encompasses pathologies of the cochlea and the auditory nerve. Hearing impairment caused by abnormal neural encoding of ...sound stimuli despite preservation of sensory transduction and amplification by outer hair cells is known as 'auditory neuropathy'. This term was originally coined for a specific type of hearing impairment affecting speech comprehension beyond changes in audibility: patients with this condition report that they "can hear but cannot understand". This type of hearing impairment can be caused by damage to the sensory inner hair cells (IHCs), IHC ribbon synapses or spiral ganglion neurons. Human genetic and physiological studies, as well as research on animal models, have recently shown that disrupted IHC ribbon synapse function--resulting from genetic alterations that affect presynaptic glutamate loading of synaptic vesicles, Ca(2+) influx, or synaptic vesicle exocytosis--leads to hearing impairment termed 'auditory synaptopathy'. Moreover, animal studies have demonstrated that sound overexposure causes excitotoxic loss of IHC ribbon synapses. This mechanism probably contributes to hearing disorders caused by noise exposure or age-related hearing loss. This Review provides an update on recently elucidated sensory, synaptic and neural mechanisms of hearing impairment, their corresponding clinical findings, and discusses current rehabilitation strategies as well as future therapies.
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