Unilateral auditory neuropathy caused by cochlear nerve deficiency

A systematic review on the imaging findings in auditory neuropathy spectrum disorder

Purpose

The present systematic review examined imaging findings in the Auditory Neuropathy Spectrum Disorder (ANSD) population.

Methods

Electronic databases such as Pub Med, Google Scholar, J Gate, and Science Direct were used to conduct a literature search. The articles retrieved through the literature search were assessed in two stages. In the first stage, title and abstract screening were done; in the second stage, a full-length article review was done. From the 379 shortlisted records, 19 articles were chosen for the full-length review.

Results

The selected articles performed imaging using Computerized tomography (CT) and magnetic resonance imaging (MRI). In most studies, cochlear nerve deficiency (CND) was the most prevalent anomaly in the ANSD group. Also, MRI was the imaging modality of choice recommended in most studies. It was also noted that CND was a characteristic feature of unilateral ANSD.

Conclusion

From this systematic review, it is clear that integrating imaging studies into diagnostic protocol would help to understand the underlying pathology better and expedite decision-making and intervention for ANSD patients.

Audiological Features in 63 Patients With Cochlear Nerve Deficiency

OBJECTIVE

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.

STUDY DESIGN

Retrospective observational nonrandomized group study.

SETTING

Academic medical center.

PATIENTS/INTERVENTIONS

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.

MAIN OUTCOME MEASURES

Imaging tests by MRI and CT and audiometric assessments by pure-tone audiometry and distortion product otoacoustic emission were performed.

RESULTS

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.

CONCLUSIONS

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.

Clinical characteristics of patients with unilateral auditory neuropathy

OBJECTIVE

To analyze the clinical characteristics of patients with unilateral auditory neuropathy (UAN), and to provide guidance for future clinical diagnosis and research.

METHODS

Patients who were clinically diagnosed with UAN from 2004 to 2019 were included. Clinical characteristics, audiological features, imaging findings, genetic test results and management effect were summarized and followed.

RESULTS

A total of 44 patients [mean age, 4.35 ± 4.39 years; 22 (50.00%) males and 22 (50.00%) females] were enrolled for analyses. Among the 38 patients who were tested by pure-tone or behavioral audiometry, the degree of hearing loss of the affected ear was characterized as mild in 2 ears (5.26%), moderate in 5 (13.16%), severe in 9 (23.68%) and profound in 22 (57.89%). For the 44 contralateral ears, 33 (75.00%) showed normal hearing and 11 (25.00%) presented with sensorineural hearing loss. Auditory brainstem responses were absent or abnormal in all 44 affected ears, while otoacoustic emissions and/or cochlear microphonics were present. Among the 18 patients who underwent magnetic resonance imaging (MRI), 7 (38.89%) presented cochlear nerve deficiency (CND). Nineteen candidate variants were found in 12 patients among the 15 UAN patients who were conducted targeted gene capture and next generation sequencing. Thirty patients were followed up by telephone to investigate their management effect.

CONCLUSIONS

Our study demonstrates comprehensive audiological features of patients with UAN to improve the clinical understanding and diagnosis. Some patients with UAN could show ipsilateral CND and MRI is essential to evaluate if the nerve is deficient. No pathogenic variants that directly related to the pathogenesis of UAN have been found in this study currently.

Effect of Quiet and Noise on P300 Response in Individuals with Auditory Neuropathy Spectrum Disorder

Introduction  Auditory neuropathy spectrum disorder (ANSD) is a clinical condition in which individuals have normal cochlear responses and abnormal neural responses. There is a lack of evidence in the literature regarding the neural discrimination skill in individuals with ANSD, especially when the signal is presented in the presence of noise. Objectives  The present study was performed with the aim to investigate auditory discrimination skill, in quiet and in the presence of noise, in individuals with ANSD and to compare the findings with normal-hearing individuals. Methods  A total of 30 individuals with normal hearing sensitivity and 30 individuals with ANSD in the age range of 15 to 55 years old, with the mean age of 27.86 years old, were the participants. P300 response was recorded from both groups using syllable pairs /ba/-/da/ in oddball paradigm and the syllable /da/ in repetitive paradigm in quiet and at +10 dB signal-to-noise ratio (SNR). Results  There was significant prolongation in latency and reaction time, and reduction in amplitude of P300 response and sensitivity in both groups with the addition of noise. The topographic pattern analysis showed activation of the central-parietal-occipital region of the brain in individuals with ANSD, whereas activation of the central-parietal region was observed in individuals with normal hearing. The activation was more diffused in individuals with ANSD compared with that of individuals with normal hearing. Conclusion  The individuals with ANSD showed a significantly more adverse effect of noise on the neural discrimination skill than the normal counterpart.

Effect of acoustic features on discrimination ability in individuals with auditory neuropathy spectrum disorder: an electrophysiological and behavioral study

PURPOSE

The present study aimed to investigate the discrimination ability for acoustic cues in individuals with auditory neuropathy spectrum disorder (ANSD) using both behavioral and neural measures and to compare the result with normal hearing individuals.

METHODS

Four naturally produced syllables /ba/, /da/, /ma/ and /pa/ were used to study discrimination skills. They were combined in pairs such that the two syllables differ in acoustic features, that is place (/ba/-/da/), manner (/ba/-/ma/) and voicing (/ba/-/pa/) cues. Thirty individuals with ANSD and 30 individuals with normal hearing sensitivity were the participants. Syllable discrimination skill was assessed using behavioral (reaction time, sensitivity and D-prime) and neural (P300) measures.

RESULTS

There was prolongation in latency and reduction in amplitude of P300 in individuals with ANSD compared to individuals with normal hearing sensitivity. Individuals with ANSD showed better discrimination skill for stimulus pairs differing in the manner followed by place and the least perceived was voicing information.

CONCLUSION

Discrimination ability of individuals with ANSD is found to be affected as evident on behavioral and neural measures. The discrimination ability varies with acoustic features of speech.

Extremely common radiographic finding of cochlear nerve deficiency among infants with prelingual single-sided deafness and its clinical implications

OBJECTIVES

To clarify the common radiographic findings of audiologically documented prelingual single-sided deafness (SSD) and identify the prevalence of cochlear nerve deficiency (CND) in SSD infants referred from the newborn hearing screening program.

METHODS

Between March 2012 and March 2017, the records of all infants referred to our otology clinic after undergoing newborn hearing screening program were retrospectively reviewed. Twenty-four consecutive well infants without risk factors who had a confirmed diagnosis of prelingual SSD under the age of 1 year and who underwent internal auditory canal (IAC) magnetic resonance imaging (MRI) were included. The sizes of cochlear nerve (CN), IAC, and cochlear nerve canal (CNC) were measured on MRI. The presence of CND was visually determined by comparing the CN size to the ipsilateral facial nerve (FN) in the affected side via an oblique sagittal view of IAC MRI and defined when CN was absent or smaller than FN.

RESULTS

CND was seen in all 24 deaf ears (100%) on MRI. There was one with incomplete partition type I, and another with combined cochleovestibular nerve absence. Twenty-four subjects demonstrated either an absent (20/24, 83.3%) or small (4/24, 16.7%) CN. When the absent and small CN groups were compared, the former group had a higher prevalence of narrow CNC and narrow IAC. Of the 20 infants without identifiable CN on the affected side, 17 (85%) had narrow IAC and 17 (85%) had narrow CNC. In the 20 ears with absent CN, only one had both normal-sized IAC and CNC.

CONCLUSION

The contribution of CND to prelingual SSD in Korean infants reached 100%, according to IAC MRI alone.

Visualizing the 3D cytoarchitecture of the human cochlea in an intact temporal bone using synchrotron radiation phase contrast imaging

The gold standard method for visualizing the pathologies underlying human sensorineural hearing loss has remained post-mortem histology for over 125 years, despite awareness that histological preparation induces severe artifacts in biological tissue. Historically, the transition from post-mortem assessment to non-invasive clinical biomedical imaging in living humans has revolutionized diagnosis and treatment of disease; however, innovation in non-invasive techniques for cellular-level intracochlear imaging in humans has been difficult due to the cochlea's small size, complex 3D configuration, fragility, and deep encasement within bone. Here we investigate the ability of synchrotron radiation-facilitated X-ray absorption and phase contrast imaging to enable visualization of sensory cells and nerve fibers in the cochlea's sensory epithelium in situ in 3D intact, non-decalcified, unstained human temporal bones. Our findings show that this imaging technique resolves the bone-encased sensory epithelium's cytoarchitecture with unprecedented levels of cellular detail for an intact, unstained specimen, and is capable of distinguishing between healthy and damaged epithelium. All analyses were performed using commercially available software that quickly reconstructs and facilitates 3D manipulation of massive data sets. Results suggest that synchrotron radiation phase contrast imaging has the future potential to replace histology as a gold standard for evaluating intracochlear structural integrity in human specimens, and motivate further optimization for translation to the clinic.

Visualizing the 3D cytoarchitecture of the human cochlea in an intact temporal bone using synchrotron radiation phase contrast imaging

The gold standard method for visualizing the pathologies underlying human sensorineural hearing loss has remained post-mortem histology for over 125 years, despite awareness that histological preparation induces severe artifacts in biological tissue. Historically, the transition from post-mortem assessment to non-invasive clinical biomedical imaging in living humans has revolutionized diagnosis and treatment of disease; however, innovation in non-invasive techniques for cellular-level intracochlear imaging in humans has been difficult due to the cochlea's small size, complex 3D configuration, fragility, and deep encasement within bone. Here we investigate the ability of synchrotron radiation-facilitated X-ray absorption and phase contrast imaging to enable visualization of sensory cells and nerve fibers in the cochlea's sensory epithelium in situ in 3D intact, non-decalcified, unstained human temporal bones. Our findings show that this imaging technique resolves the bone-encased sensory epithelium's cytoarchitecture with unprecedented levels of cellular detail for an intact, unstained specimen, and is capable of distinguishing between healthy and damaged epithelium. All analyses were performed using commercially available software that quickly reconstructs and facilitates 3D manipulation of massive data sets. Results suggest that synchrotron radiation phase contrast imaging has the future potential to replace histology as a gold standard for evaluating intracochlear structural integrity in human specimens, and motivate further optimization for translation to the clinic.

Diverse etiologies manifesting auditory neuropathy characteristics from infants with profound hearing loss and clinical implications

OBJECTIVE

Auditory neuropathy spectrum disorder (ANSD) is a hearing disorder with impaired signal transmission from the inner ear to the brain. The electrophysiological characteristics of auditory neuropathy (AN characteristics) are marked with presence of otoacoustic emissions (OAE) or cochlear microphonics (CM) in the absence of auditory brainstem response (ABR). This study aimed to review etiologies related to AN characteristics from infants with profound hearing loss (HL), either unilaterally or bilaterally.

STUDY DESIGN

Prospective cohort study for thirty infants with prelingual profound HL.

METHODS

ABR, OAE, and/or CM were analyzed to identify electrophysiological characteristics. Temporal bone computed tomography and/or internal acoustic canal magnetic resonance imaging were reviewed to identify anatomical abnormalities. The electrophysiological characteristics and cochlear nerve status were analyzed according to the laterality of deafness (unilateral vs bilateral).

RESULTS

Among the total 41 ears (from 30 infants) with profound HL, 13 ears (7 (36.8%) of 19 ears with unilateral HL and 6 (27.3%) of 22 ears associated with bilateral HL) showed AN characteristics (37.1%), and 21 ears showed cochlear nerve deficiency (CND) (51.2%). AN characteristics was detected about two times more frequently in cases with CND (38.1%) than with anatomically normal cochlear nerve (20.0%), the difference not reaching a statistical significance probably due to a small sample size. Detection of AN characteristics did not differ between unilateral and bilateral profound HL, even though presence of CND was more frequently detected in cases with unilateral profound HL than with bilateral cases. There were at least five types of etiologies related to AN characteristics in 13 ears (from 10 infants) in our series depending on the laterality of deafness and presence of CND.

CONCLUSIONS

This study demonstrates that there were diverse etiologies related to AN characteristics from infants with unilateral or bilateral profound HL. Association between CND and AN characteristics is suggestive but not solid at this moment and AN characteristics is not a fully penetrant feature of CND.

Auditory neuropathy spectrum disorder: a review

PURPOSE

Auditory neuropathy spectrum disorder, or ANSD, can be a confusing diagnosis to physicians, clinicians, those diagnosed, and parents of children diagnosed with the condition. The purpose of this review is to provide the reader with an understanding of the disorder, the limitations in current tools to determine site(s) of lesion, and management techniques.

METHOD

This article is a review of what is known about ANSD. It includes descriptions of assessment tools, causes of ANSD, and patient management techniques.

CONCLUSIONS

This review is a guide to audiologists, speech-language pathologists, and early interventionists who work with individuals diagnosed with ANSD and/or their families. It highlights the need for more precise tools to describe the disorder in order to facilitate decisions about interventions and lead to better predictions of outcome.

Speech processing disorder in neural hearing loss

Deficits in central auditory processing may occur in a variety of clinical conditions including traumatic brain injury, neurodegenerative disease, auditory neuropathy/dyssynchrony syndrome, neurological disorders associated with aging, and aphasia. Deficits in central auditory processing of a more subtle nature have also been studied extensively in neurodevelopmental disorders in children with learning disabilities, ADD, and developmental language disorders. Illustrative cases are reviewed demonstrating the use of an audiological test battery in patients with auditory neuropathy/dyssynchrony syndrome, bilateral lesions to the inferior colliculi, and bilateral lesions to the temporal lobes. Electrophysiological tests of auditory function were utilized to define the locus of dysfunction at neural levels ranging from the auditory nerve, midbrain, and cortical levels.