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Traditional approaches to the human cochlear nerve have been impeded by its bony encasement deep inside the skull base. We present an innovative, minimally invasive, therapeutic pathway for direct access to the nerve to deliver novel regenerative therapies. Neuroanatomical studies on 10 cadaveric human temporal bones were undertaken to identify a potentially safe therapeutic pathway to the cochlear nerve. Simulations based on three-dimensional delineation of anatomical structures obtained from synchrotron phase-contrast imaging were analyzed. This enabled the identification of an approach to the nerve in the fundus of the internal auditory meatus by trephining the medial modiolar wall of the cochlea via the round window for a median depth of 1.48 mm (range 1.21–1.91 mm). The anatomical access was validated on 9 additional human temporal bones using radio-opaque markers and contrast injection with micro-computed tomography surveillance. We thus created an effective conduit for the delivery of therapeutic agents to the cochlear nerve. [ABSTRACT FROM AUTHOR]

Abstract Traditional approaches to the human cochlear nerve have been impeded by its bony encasement deep inside the skull base. We present an innovative, minimally invasive, therapeutic pathway for direct access to the nerve to deliver novel regenerative therapies. Neuroanatomical studies on 10 cadaveric human temporal bones were undertaken to identify a potentially safe therapeutic pathway to the cochlear nerve. Simulations based on three-dimensional delineation of anatomical structures obtained from synchrotron phase-contrast imaging were analyzed. This enabled the identification of an approach to the nerve in the fundus of the internal auditory meatus by trephining the medial modiolar wall of the cochlea via the round window for a median depth of 1.48 mm (range 1.21–1.91 mm). The anatomical access was validated on 9 additional human temporal bones using radio-opaque markers and contrast injection with micro-computed tomography surveillance. We thus created an effective conduit for the delivery of therapeutic agents to the cochlear nerve.

Background: Quick and appropriate diagnostics and the use of intraoperative monitoring (IM) of hearing during vestibular schwannoma (VS) resection increase the likelihood of hearing preservation. During surgery, various methods of IM can be used, i.e., auditory brainstem responses (ABRs), transtympanic electrocochleography (TT-ECochG), and direct cochlear nerve action potentials. The aim of the study was to evaluate the prognostic values of IM of hearing using ABR and TT-ECochG in predicting postoperative hearing preservation and to evaluate relationships between them during various stages of surgery. Methods: This retrospective study presents the pre- and postoperative audiological test results and IM of hearing records (TT-ECochG and ABR) in 75 (43 women, 32 men, aged 18–69) patients with diagnosed VS. Results: The preoperative pure tone average hearing threshold was 25.02 dB HL, while after VS resection, it worsened on average by 30.03 dB HL. According to the American Academy of Otolaryngology–Head and Neck Surgery (AAO—HNS) Hearing Classification, before and after (pre/post) surgery, there were 47/24 patients in hearing class A, 9/8 in B, 2/1 in C, and 17/42 in D. In speech audiometry, the average preoperative speech discrimination score at an intensity of 60 dB SPL was 70.93%, and after VS resection, it worsened to 38.93%. The analysis of electrophysiological tests showed that before the tumor removal the I–V ABR interlatencies was 5.06 ms, and after VS resection, it was 6.43 ms. Conclusions: The study revealed correlations between worse postoperative hearing and changes in intraoperatively measured ABR and TT-ECochG. IM of hearing is very useful in predicting postoperative hearing in VS patients and increases the chance of postoperative hearing preservation in these patients. [ABSTRACT FROM AUTHOR]

Background and Objectives: Idiopathic sudden sensorineural hearing loss (ISSHL) is a rapid loss of hearing, exceeding 30 dB in at least 3 consecutive frequencies within 3 days, without any identifiable cause despite thorough investigations. Currently, the etiology and pathogenesis of ISSHL have not been fully elucidated. This study aimed to assess the size of the cochlear nerve in patients with ISSHL and explore its relationship with pretreatment audiograms and treatment response. Subjects and Methods: A total of 125 patients (59 [47.2%] women; mean age 47.7±13.8 years [minimum-maximum: 21-76]) and 60 healthy participants (27 [45%] women; mean age 45.7±16.8 years [minimum-maximum: 20-76]) as a control group were included in this study. The size of the cochlear nerve was assessed on the affected side, compared to the control group, as well as on the unaffected side. Pretreatment and posttreatment audiological values were also analyzed. Results: The cross-sectional area (CSA), vertical diameter (VD), and horizontal diameter (HD) of the CN were found to be smaller on the affected side of ISSHL patients compared to the control group (p<0.01; p=0.04; p=0.02, respectively). In the study group (affected side of ISSHL patients), there were no significant differences in VD, HD, and CSA values between pretreatment audiogram types (p=0.23; p=0.53; p=0.39, respectively), and initial hearing levels (p=0.16; p=0.22; p=0.23, respectively). Furthermore, there were no significant differences in VD, HD, and CSA values between the recovery groups according to Furuhashi criteria (p=0.18; p=0.37; p=0.27, respectively). Conclusions: The size of the CN may be a risk factor for ISSHL, but it does not affect the type of audiogram curves and was not prognostic in terms of treatment response. [ABSTRACT FROM AUTHOR]

Background: Cochlear implantation (CI) outcomes in patients with auditory neuropathy (AN) are variable, which hampers patients' decisions on CI. Objective: This study aims to assess the outcomes of CI in individuals diagnosed with AN and to examine the various factors that may influence the effectiveness of this intervention. Methods: A total of 75 patients diagnosed with AN were included in the study. The hearing threshold, the score of categories of auditory performance (CAP), speech intelligibility rating (SIR), and speech audiometry were tested. Genetic testing was conducted by medical exome sequencing in 46 patients. Results: After CI, the average aided hearing threshold for patients with prelingual and post-lingual onset was 38.25 ± 6.63 dB and 32.58 ± 9.26 dB, respectively; CAP score improved to 5.52 ± 1.64 (p < 0.001) and 6.00 ± 0.96 (p < 0.001), respectively; SIR score increased to 3.57 ± 1.22 (p < 0.001) and 4.15 ± 0.95 (p < 0.001), respectively. Maximum speech recognition ranged from 58 to 93% for prelingual onset patients and 43 to 98% for those with post-lingual onset. Speech outcomes of CI in cases with cochlear nerve (CN) deficiency were significantly poorer (p = 0.008). Molecular etiologies, including TWIST1, ACTG1, m.A7445G, and a copy-number variant (CNV) carrying ACTB, were related to AN here. Conclusion: CI is a viable therapy option for patients with AN; CN deficiency might impact outcomes of CI. [ABSTRACT FROM AUTHOR]

The diagnosis of large vestibular schwannomas (VS) with retained useful hearing has become increasingly common. Preservation of facial nerve (FN) function has improved using intraoperative EMG monitoring, hearing preservation remains challenging, with the recent use of cochlear nerve action potential (CNAP) monitoring. This prospective longitudinal series of VS with useful hearing operated on using a retrosigmoid approach included 37 patients with a mean largest extrameatal VS. diameter of 25 ± 8.7 mm (81% of Koos stage 4). CNAP was detected in 51% of patients, while auditory brainstem responses (ABR) were present in 22%. Patients were divided into two groups based on the initial intraoperative CNAP status, whether it was present or absent. FN function was preserved (grade I–II) in 95% of cases at 6 months. Serviceable hearing (class A + B) was preserved in 16% of the cases, while 27% retained hearing with intelligibility (class A–C). Hearing with intelligibility (class A–C) was preserved in 42% of cases when CNAP could be monitored in the early stages of VS resection versus 11% when it was initially absent. Changes in both the approach to the cochlear nerve and VS resection are mandatory in preserving CNAP and improve the rate of hearing preservation. [ABSTRACT FROM AUTHOR]

Objective: The aim of this study is to evaluate the relationship between the cochlear nerve and the anatomical structures of the cochlea and internal acoustic canal in patients with congenital hearing loss. Materials and Methods: Temporal tomography and magnetic resonance images of 44 patients (88 ears) with non-syndromic congenital hearing loss were retrospectively analyzed between 2018 and 2021. Patients were divided into 2 groups according to cochlear nerve hypoplasia. Cochlear nerve canal width, cochlear basal/ middle turn widths, and internal auditory canal widths were examined. Results: Cochlear nerve hypoplasia was detected in 18.2% (n = 16) of the patients and all of the patients with cochlear nerve hypoplasia had severe hearing loss. A statistically significant difference was found between the structures' widths in patients with and without cochlear nerve hypoplasia, in cochlear nerve canal and coronal width of the internal auditory canal. When stenosis is accepted as <1.4 mm for cochlear nerve canal and <3.80 mm for coronal width of the internal auditory canal, cochlear nerve hypoplasia differs statistically between the groups in measurements (respectively; P < .001, P = .018). Conclusions: In patients with sensorineural hearing loss, cochlear nerve hypoplasia may accompany. Anatomical structures are important in predicting cochlear nerve hypoplasia from temporal computed tomography. Cochlear nerve hypoplasia should be suspected if the cochlear nerve canal and coronal width of the internal auditory canal are less than 1.4 mm and 3.8 mm, respectively, on temporal computed tomography. [ABSTRACT FROM AUTHOR]

Introduction:Incomplete partition (IP) type and accompanying cochlear nerve (CN) anomalies affect the patient’s management. We revealed the cochlear nerve area (CNA), cochlear nerve canal width (CNCW), and inner auditory canal width (IACW) of IP types.Methods:We retrospectively scanned patients with IP. There were 88 IP ears (26 IP type 1, 54 IP type 2, 8 IP type 3) and 54 controls. The CNCW and IACW were measured in axial temporal computed tomography sections. The CNA and facial nerve area (FNA) were measured in the distal IAC on the sagittal-oblique plane of 3D constructive interference steady-state T2-weighted magnetic resonance images.Results:CNA and CNA/FNA values for each IP type differed significantly compared with the control group. However, the CNCW and IACW values did not differ significantly. The CNA was the least in IP 1 cases. Five CN aplasia were detected, and all were associated with IP type 1 anomaly (3.5% of all, 5.6% of IP types, and 19.2% of IP type 1 cases). CN hypoplasia was observed in 10 IP type 1 (38.5% of IP 1), 6 IP type 2 (6.8% of IP type 2), and 1 IP type 3 (12.5% of IP type 3) ears. None of the CN hypoplasia had a CNC hypoplasia.Conclusion:CN aplasia and hypoplasia most frequently accompanied with IP type 1 in our study. Therefore, they need an extra interest in CN evaluation. CNCW and IACW are not very useful in predicting CN dysplasia in IP cases.

BACKGROUND: Idiopathic sudden sensorineural hearing loss is a disabling condition that lowers the quality of life specifically in older adults living alone. It is crucial to determine the outcome of the disease and to offer early treatment to prevent isolation caused by hearing impairment in this population. The objective of our study was to investigate whether the initial cochlear nerve thickness may predict the outcome of hearing recovery in older adults with idiopathic sudden sensorineural hearing loss. METHODS: The study population was composed of older adults that were referred with idiopathic sudden sensorineural hearing loss in 1 ear. Long-term audiological data of the cohort were analyzed according to Siegel's criteria on hearing recovery and were grouped according to complete recovery or treatment failure. Cochlear nerve diameters of the diseased and safe ears of each group, measured on reformatted images on magnetic resonance imaging, at the fundus, in the mid-internal acoustic canal, and at the entry point into the Pons were compared in each group and between groups. RESULTS: Mean cochlear nerve diameter was significantly larger in the recovered older adults (1.11 ± 0.27 mm) than in the non-recovered adults (0.94 ± 0.21 mm) at the mid-internal acoustic canal (Student's t-test, P < .05). Cochlear nerve thickness at mid-internal acoustic canal (≤0.8 mm) sensitivity for recovery failure was 89% and displayed an odds ratio 5.333, 95% CI (1.000-28.435). CONCLUSION: Cochlear nerve thickness in mid-internal acoustic canal in non-recovered older adults with idiopathic sudden sensorineural hearing loss is significantly thinner than the completely recovered group. Older adults with mid-internal acoustic canal cochlear nerve greatest diameter cutoff level of ≤0.8 mm are 5.33 times more exposed to recovery failure. [ABSTRACT FROM AUTHOR]

With the recent scientific and technical developments, hearing preservation surgery is becoming a growing objective in inner ear pathologies, especially for vestibular schwannomas. In this review, we aim to describe the pros and cons of the following cochlear nerve monitoring techniques: ABRs (auditory brainstem responses), DENM (direct eighth cranial nerve monitoring), EcochG (electrocochleography), CNAP (cochlear compound nerve action potentials), DPOAE (distortion product otoacoustic emissions), PAMRs (postauricular muscle responses). The Cochrane library, Scopus, DynaMed, and PubMed databases were screened to obtain any relevant papers from October 2009 to the present day. Due to the heterogeneity of the existing studies in the literature, there is no way to tell whether a technique is better than another. All authors reported satisfactory outcomes with the cochlear nerve monitoring techniques tested, either alone or in combination.

Objective To explore the application of membranous concept in vestibular schwannoma surgery. Methods A total of 39 patients with vestibular schwannoma who received membranous surgical treatment in The First Affiliated Hospital of Anhui Medical University from May 2020 to June 2021 were enrolled. Through the retrosigmoid approach, the intraoperative electrophysiological monitoring was performed, and the membranous concept was used to separate the brain stem of the tumor and the interface between the tumor and the facial nerve and the cochlear nerve. Facial nerve function was evaluated by the House⁃Brackmann (H⁃B) grade and hearing was evaluated by the American Academy of Otolaryngology⁃Head and Neck Surgery（AAO⁃HNS）scale at one day, one week and one year after surgery. Results Total resection was performed in 31 cases (79.49%) and nearly total resection in 8 cases (20.51%). Facial nerve anatomical preservation was achieved in all patients, and facial nerve function returned to normal or nearly normal (H⁃B grade Ⅰ-Ⅱ) 84.62% (33/39), moderate facial paralysis (H⁃B grade Ⅲ) 10.27% (4/39), moderate and severe facial paralysis (H⁃B grade Ⅳ) 5.13% (2/39) on the first day after surgery. One week after surgery, 71.79% (28/39) of patients with normal or nearly normal facial nerve function, 15.38% (6/39) of moderate facial paralysis, 10.27% (4/39) of moderate and severe facial paralysis, and 2.56% (1/39) of severe facial paralysis (H⁃B grade Ⅴ). One year after surgery, 92.31% (36/39) of patients with facial nerve function returned to normal or nearly normal, 5.13% (2/39) of patients with moderate facial paralysis, and 2.56% (1/39) of patients with moderate and severe facial paralysis. Among the 10 patients (25.64%) who retained effective hearing before surgery (AAO⁃HNS grade≥C), there were 4, 3 and 6 cases at one day, one week and one year after surgery, respectively. Those who did not retain effective hearing before surgery did not recover effective hearing after surgery. According to the comparison of tumor volume and nature, the proportion of patients with normal facial nerve function (H⁃B grade Ⅰ) in the tumor volume≤3 cm group was higher than that in＞3 cm group [12/18 vs. 19.05% (4/21); Fisher's exact probability: P=0.006], the proportion of patients with normal facial nerve function in the solid tumor group was higher than that in cystic group [71.43% (15/21) vs. 1/10; Fisher's exact probability: P=0.010] at one year after surgery. Conclusions The membranous concept in vestibular schwannoma surgery can protect facial nerve function well, and has a positive effect on the protection of cochlear nerve and brain stem.

The Trans-labrynthine approach, through Otic capsule gives direct approach to the cerebellopontine angle (CPA) and internal auditory meatus (IAM) with preservation of the facial nerve. Mastering the approach to IAM in a cadaver with anatomical landmarks is important to the budding Otologist & Neurotologist to approach the CPA with functional preservation of the Facial nerve in patients with Vestibular Schwannoma & other procedures. Transitioning surgical skills and anatomic knowledge from surgical anatomy textbooks and laboratory training to the operative room is challenging. 30 adult wet human cadaveric temporal bones were studied by performing Trans-labrynthine approach to the IAM by using ZEISS microscope in a temporal bone dissection lab. Photographs were taken by HD phone camera, imported into computer & labeled the anatomical landmarks. Wide exposure & 3D visualization of complex anatomical landmarks were noted in each step by step approach from basic to advanced procedure of Trans-labrynthine approach to IAM. The step by step approach to the IAM from basic to advanced procedure in a cadaveric temporal bone offers great orientation & opportunity to become a master of the complex surgical anatomy of IAM and in acquiring a 3D orientation of the critical structures. [ABSTRACT FROM AUTHOR]

Local and privileged expression of dendritic proteins allows segregation of distinct functions in a single neuron but may represent one of the underlying mechanisms for early and insidious presentation of sensory neuropathy. Tangible characteristics of early hearing loss (HL) are defined in correlation with nascent hidden hearing loss (HHL) in humans and animal models. Despite the plethora of causes of HL, only two prevailing mechanisms for HHL have been identified, and in both cases, common structural deficits are implicated in inner hair cell synapses, and demyelination of the auditory nerve (AN). We uncovered that Na+-activated K+ (KNa) mRNA and channel proteins are distinctly and locally expressed in dendritic projections of primary ANs and genetic deletion of KNa channels (Kcnt1 and Kcnt2) results in the loss of proper AN synaptic function, characterized as HHL, without structural synaptic alterations. We further demonstrate that the local functional synaptic alterations transition from HHL to increased hearing-threshold, which entails changes in global Ca2+ homeostasis, activation of caspases 3/9, impaired regulation of inositol triphosphate receptor 1 (IP3R1), and apoptosis-mediated neurodegeneration. Thus, the present study demonstrates how local synaptic dysfunction results in an apparent latent pathological phenotype (HHL) and, if undetected, can lead to overt HL. It also highlights, for the first time, that HHL can precede structural synaptic dysfunction and AN demyelination. The stepwise cellular mechanisms from HHL to canonical HL are revealed, providing a platform for intervention to prevent lasting and irreversible age-related hearing loss (ARHL).

Noninvasive transcranial electric stimulation is increasingly being used as an advantageous therapy alternative that may activate deep tissues while avoiding drug side-effects. However, not only is there limited evidence for activation of deep tissues by transcranial electric stimulation, its evoked human sensation is understudied and often dismissed as a placebo or secondary effect. By systematically characterizing the human sensation evoked by transcranial alternating-current stimulation, we observed not only stimulus frequency and electrode position dependencies specific for auditory and visual sensation but also a broader presence of somatic sensation ranging from touch and vibration to pain and pressure. We found generally monotonic input-output functions at suprathreshold levels, and often multiple types of sensation occurring simultaneously in response to the same electric stimulation. We further used a recording circuit embedded in a cochlear implant to directly and objectively measure the amount of transcranial electric stimulation reaching the auditory nerve, a deep intercranial target located in the densest bone of the skull. We found an optimal configuration using an ear canal electrode and low-frequency (

Objective:To reveal the correlation between implantation age, the internal acoustic canal (IAC) width, bony cochlear nerve canal (BCNC) width, and auditory performance in primary school children with bilateral cochlear implantation (CI).Methods:Preoperative IAC and BCNC widths of 57 pre-lingually deaf children aged 7–11 years who had previously undergone bilateral CI in our institution were reviewed and cut-off values were calculated. Twenty-four patients who had additional problems and could not attend school and those who refused to participate in the study were excluded. The remaining 33 were invited to the hospital, and their speech perception tests, and language development scores were analyzed (16 of 33 patients had been operated on before the age of 24 months).Results:The cut-off values calculated from the 114 ears of 57 patients were 3.86 mm for IAC width and 1.56 mm for BCNC width. The auditory performances of the 33 patients after CI were not significantly different in the narrow and normal width groups. However, speech perception test results, and language development scores of patients implanted before the age of 24 months were significantly higher.Conclusion:There are some studies showing that children with bilateral sensorineural hearing loss have narrower IAC and BCNC widths. However, we concluded that the widths of the IAC and the bone cochlear nerve canal did not affect auditory performance. We found that implantation age is the single most important determinant of speech-language development after CI.

Electrical stimulation of the auditory nerve with a penetrating intraneural (IN) electrode in acutely deafened cats produces much more restricted spread of excitation than is obtained in that preparation with a conventional cochlear implant (CI) as reported by Middlebrooks and Snyder (J Assoc Res Otolaryngol 8:258-279, 2007). That suggests that a future auditory prosthesis employing IN stimulation might offer human patients greater frequency selectivity than is available with a present-day CI. Nevertheless, it is a concern that the electrical field produced by an IN electrode might be too restricted to produce adequate stimulation of the partially depopulated auditory nerve of a deaf patient. We evaluated this by testing responses to IN and CI stimulation in adult-deafened cats. Activation of the auditory pathway was monitored by recording from the central nucleus of the inferior colliculus (ICC). Cats deaf for 153-277 days exhibited a ~ 30 % loss of auditory nerve fibers compared to cats deaf for

With the recent scientific and technical developments, hearing preservation surgery is becoming a growing objective in inner ear pathologies, especially for vestibular schwannomas. In this review, we aim to describe the pros and cons of the following cochlear nerve monitoring techniques: ABRs (auditory brainstem responses), DENM (direct eighth cranial nerve monitoring), EcochG (electrocochleography), CNAP (cochlear compound nerve action potentials), DPOAE (distortion product otoacoustic emissions), PAMRs (postauricular muscle responses). The Cochrane library, Scopus, DynaMed, and PubMed databases were screened to obtain any relevant papers from October 2009 to the present day. Due to the heterogeneity of the existing studies in the literature, there is no way to tell whether a technique is better than another. All authors reported satisfactory outcomes with the cochlear nerve monitoring techniques tested, either alone or in combination. [ABSTRACT FROM AUTHOR]

Introduction: Electrically evoked auditory brainstem responses provide reliable clinical information to assist professionals in the auditory rehabilitation of cochlear implant users. Objective: This study aimed to investigate intraoperative evoked auditory brainstem response recordings in Evo®-cochlear implant electrode array recipients and its correlation with their behavioral levels and auditory performance. Methods: : This is a retrospectivey study. Intraoperative evoked auditory brainstem responses were recorded in adult Evo®-cochlear implant electrode array recipients. Wave V latencies, amplitudes and interpeak III–V intervals were recorded in three different electrode locations and compared to the sentence recognition scores obtained from subjects after six months of device use. Evoked auditory brainstem responses thresholds were also recorded and compared to the behaviorally determined levels of the subjects in the sound processor activation. Results: Evoked auditory brainstem responses thresholds were significantly correlated with both, behavioral T- and C-levels and they were recorded at audible electrical stimulation levels in all subjects. There was a significant correlation between interpeak III–V interval recorded in the apical electrode and sentence recognition scores of the subjects. Conclusions: Intraoperative evoked auditory brainstem responses can be used to establish audible levels for fitting the sound processor in Evo®-cochlear implant recipients and it could help professionals to plan further actions aiming to improve their auditory performance.

Artificial cochlea or cochlear implant is the name for neurosensory prosthesis, which is a current surgical treatment for severe hearing loss or deafness.The surgical procedure is cochlear implantation During the cochlear implantation one of the methods of neural response measuring of the auditory nerve to electrical stimulation is telemetry. It is an integral part of the cochlear implantation procedure. Telemetry determines audibility thresholds, stimulus discomfort thresholds, and dynamic range. With objective parameters, in telemetry we also estimate psychoacoustic parameters, which are the basis of simulation maps for the future hearing rehabilitation.

Introduction:To investigate the relationship between morphometric variants of the cochlear nerve (CN) and the hearing level. To investigate the confounding effects of age, sex, and audiometric variables on the relationship between CN morphometrics and hearing loss, if present.Methods:Audiological data and magnetic resonance imaging findings of 127 patients with asymmetrical sensorineural hearing loss (ASNHL) were reviewed retrospectively. According to pure tone average (PTA) frequencies of each ear, difference above 25 dB were accepted as ASNHL. The vertical (Vd) and horizontal diameters (Hd) and the cross-sectional area (CSA) of the CN were measured.Results:The difference in CSA and Vd between ears showed a negative correlation with age. The mean CSA was 1.57 in AE and 1.60 in NE. Mean Hd was 1.00 in AE and 1.00 NE. Mean Vd was 1.40 in AE and 1.50 in NE. There was no correlation between the difference ratios of thresholds and CN diameter parameters. There was no significant correlation of CSA, Vd, and Hd with PTA thresholds at each frequency.Conclusion:Aging is associated with losses in Vd diameter and CSA. The degree of hearing loss was not correlated with the morphometric features of the CN. The morphometry of the CN should be interpreted together with the etiology of hearing loss.

Vestibular schwannoma is the most common intracranial schwannoma. The treatment concept is changing from simple surgical resection to the integrated strategy of observation and follow⁃up, stereotactic radiotherapy (SRT) and surgical resection. Higher requirements are put forward for the function perservation of the facial nerve and the cochlear nerve. Neurosurgeons should pay attention to the protection of nerve function and actively develop modern vestibular schwannoma surgery.

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.

With the development of medicine, surgery has also experienced the development and evolution from traditional surgery to minimally invasive surgery, and then to super minimally invasive surgery (SMIS). Meanwhile, reducing surgical trauma and preserving and reconstructing nerve function have gradually become new goals of modern vestibular schwannoma (VS) resection surgery. The surgery of VS can be divided into hearing-preserving surgery (retrosigmoid approach and middle fossa approach) and non-hearing-preserving surgery (traditional translabyrinthine approach), according to whether the patient has practical hearing before operation. Improving the hearing preservation rate of hearing-preserving surgery and reconstructing the hearing of patients with non-hearing-preserving surgery are major challenges and hotspots. The traditional translabyrinthine approach has the highest proportion in the Department of Otolaryngology-Head and Neck Surgery, with the advantages of high facial nerve preservation rate and few intracranial complications. However, due to the resection of the cochlear nerve and labyrinth, the cochlea develops fibrosis, and patients lose the opportunity to reconstruct hearing through cochlear implantation. The new modified translabyrinthine approach can preserve the cochlear nerve and effectively reduce cochlear fibrosis, providing an opportunity for cochlear implantation to reconstruct the hearing. This is another important breakthrough in vestibular schwannoma surgery.

Background: Magnetic resonance imaging (MRI) is used to determine whether cochlear nerve development is normal in infants and adults, but it has not yet been used to evaluate cochlear nerve development or measure cochlear nerve-related structures in the fetus. This study sought to provide imaging data for clinical evaluations concerning cochlear nerve development in the fetus using MRI., Methods: Postmortem 3.0-Tesla MRI of inner ear was performed in 51 fetuses with normal temporal bones at 25 to 40 weeks of gestation. The continuous scanning protocol incorporated axial three-dimensional (3D) sampling perfection with application-specific contrasts using different flip angle evolution sequences. The images were evaluated to measure the structures of the cochlear aperture (CA), internal auditory canal (IAC), and vestibulocochlear and facial nerves in the cerebellopontine angle (CPA), which have been reported to be associated with cochlear nerve development. We also calculated the ratio between the diameters of the vestibulocochlear and facial nerves. The measurable parameters were compared between the right and left sides. The threshold for statistical significance was set at P<0.05., Results: The inner ear anatomy was discernible on MRI in all the fetal specimens, and growth of the CA, IAC, vestibulocochlear nerve, and facial nerve in the CPA was observed as fetal age increased. There was no significant difference in the measurements of these structures between the right and left sides (all P>0.05)., Conclusions: MRI can be used to help evaluate the anatomy and development of the cochlear nerve in the fetus. These normative measurements could be valuable for clinical evaluations of the cochlear nerve., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-626/coif). C.A.M. serves as an unpaid editorial board member of Quantitative Imaging in Medicine and Surgery. The other authors have no conflicts of interest to declare., (2024 Quantitative Imaging in Medicine and Surgery. All rights reserved.)

Introduction Good hearing in pilots, including central auditory skills, is critical for flight safety and the prevention of aircraft accidents. Pure tone audiometry alone may not be enough to assess hearing in the members of this population who, in addition to high noise levels, routinely face speech recognition tasks in non-ideal conditions. Objective To characterize the frequency-following response (FFR) of a group of military pilots compared with a control group. Methods Twenty military pilots in the Study Group and 20 non-pilot military personnel, not exposed to noise in their work, in the Control Group, all with normal hearing, aged between 30 and 40 years old, completed a questionnaire to assess their hearing habits, and their FFRs were measured with a /da/ syllable (duration 40 milliseconds, speed 10.9/s), at 80 dB NA in the right ear. All procedures were approved by the ethical committee of the institution. Statistical analysis was performed using the t-Student or Mann-Whitney tests for quantitative variables, and the Fisher or chi- squared tests for qualitative variables, and a value of p<0.05 was considered to be statistically significant. Results There was no significant difference between the groups regarding auditory habits. In the FFR, wave amplitudes A (p=0.01) and C (p=0.04) were significantly lower in the Study Group. Conclusion Working as a military pilot can be a crucial factor in determining an individual’s typical FFR pattern, demonstrated in the present study by statistically significant reductions in the amplitudes of the A and C waves. [ABSTRACT FROM AUTHOR]

Mutations in the OTOF gene encoding otoferlin result in a disrupted function of the ribbon synapses with impairment of the multivesicular glutamate release. Most affected subjects present with congenital hearing loss and abnormal auditory brainstem potentials associated with preserved cochlear hair cell activities (otoacoustic emissions, cochlear microphonics [CMs]). Transtympanic electrocochleography (ECochG) has recently been proposed for defining the details of potentials arising in both the cochlea and auditory nerve in this disorder, and with a view to shedding light on the pathophysiological mechanisms underlying auditory dysfunction. We review the audiological and electrophysiological findings in children with congenital profound deafness carrying two mutant alleles of the OTOF gene. We show that cochlear microphonic (CM) amplitude and summating potential (SP) amplitude and latency are normal, consistently with a preserved outer and inner hair cell function. In the majority of OTOF children, the SP component is followed by a markedly prolonged low-amplitude negative potential replacing the compound action potential (CAP) recorded in normally-hearing children. This potential is identified at intensities as low as 90 dB below the behavioral threshold. In some ears, a synchronized CAP is superimposed on the prolonged responses at high intensity. Stimulation at high rates reduces the amplitude and duration of the prolonged potentials, consistently with their neural generation. In some children, however, the ECochG response only consists of the SP, with no prolonged potential. Cochlear implants restore hearing sensitivity, speech perception and neural CAP by electrically stimulating the auditory nerve fibers. These findings indicate that an impaired multivesicular glutamate release in OTOF-related disorders leads to abnormal auditory nerve fiber activation and a consequent impairment of spike generation. The magnitude of these effects seems to vary, ranging from no auditory nerve fiber activation to an abnormal generation of EPSPs that occasionally trigger a synchronized electrical activity, resulting in high-threshold CAPs.

PURPOSE OF REVIEW: Electric stimulation is a potent means of neuromodulation that has been used to restore hearing and minimize tremor, but its application on tinnitus symptoms has been limited. We examine recent evidence to identify the knowledge gaps in the use of electric stimulation for tinnitus treatment. RECENT FINDINGS: Recent studies using electric stimulation to suppress tinnitus in humans are categorized according to their points of attacks. First, noninvasive, direct current stimulation uses an active electrode in the ear canal, tympanic membrane, or temporal scalp. Second, inner ear stimulation uses charge-balanced biphasic stimulation by placing an active electrode on the promontory or round window, or a cochlear implant array in the cochlea. Third, intraneural implants can provide targeted stimulation of specific sites along the auditory pathway. Although these studies demonstrated some success in tinnitus suppression, none established a link between tinnitus suppression efficacy and tinnitus-generating mechanisms. SUMMARY: Electric stimulation provides a unique opportunity to suppress tinnitus. Challenges include matching electric stimulation sites and patterns to tinnitus locus and type, meeting the oftentimes-contradictory demands between tinnitus suppression and other indications, such as speech understanding, and justifying the costs and risks of electric stimulation for tinnitus symptoms.

Introduction Good hearing in pilots, including central auditory skills, is critical for flight safety and the prevention of aircraft accidents. Pure tone audiometry alone may not be enough to assess hearing in the members of this population who, in addition to high noise levels, routinely face speech recognition tasks in non-ideal conditions. Objective To characterize the frequency-following response (FFR) of a group of military pilots compared with a control group. Methods Twenty military pilots in the Study Group and 20 non-pilot military personnel, not exposed to noise in their work, in the Control Group, all with normal hearing, aged between 30 and 40 years old, completed a questionnaire to assess their hearing habits, and their FFRs were measured with a /da/ syllable (duration 40 milliseconds, speed 10.9/s), at 80 dB NA in the right ear. All procedures were approved by the ethical committee of the institution. Statistical analysis was performed using the t-Student or Mann-Whitney tests for quantitative variables, and the Fisher or chi-squared tests for qualitative variables, and a value of p

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Objective: The aim of this study was to evaluate the cochlear nerve diameter in patients with unilateral sensorineural hearing loss and to compare the diameter of the normal side with the hearing loss side. Materials and Methods: A total of 36 patients with idiopathic unilateral sensorineural hearing loss were included in the study. Magnetic resonance imaging (MRI) and audiogram were performed on all the patients. Both cochlear nerve diameters were measured on axial thin-section constructive interference in steady state (CISS) sequences. Results: The patients comprised 16 males and 20 females with a mean age of 52.3±13.7 years. Hearing loss was in the right ear in 11 patients, and in the left ear in 25. The average cochlear nerve diameter on the side with hearing loss was 0.13 cm while it was 0.19 cm on the normal side. There was a statistically significant difference between the two sides (p lt; 0.001). Conclusion: In patients with unilateral sensorineural hearing loss, MRI allows the assessment of the cochlear nerve with anatomic detail, and enables the exclusion of possible organic pathologies. Demonstration of decreased cochlear nerve diameter in idiopathic sensorineural hearing loss will contribute to elucidating the etiology of this disease in the future.

Abnormal auditory adaptation is a standard clinical tool for diagnosing auditory nerve disorders due to acoustic neuromas. In the present study we investigated auditory adaptation in auditory neuropathy owing to disordered function of inner hair cell ribbon synapses (temperature-sensitive auditory neuropathy) or auditory nerve fibres. Subjects were tested when afebrile for (i) psychophysical loudness adaptation to comfortably-loud sustained tones; and (ii) physiological adaptation of auditory brainstem responses to clicks as a function of their position in brief 20-click stimulus trains (#1, 2, 3 … 20). Results were compared with normal hearing listeners and other forms of hearing impairment. Subjects with ribbon synapse disorder had abnormally increased magnitude of loudness adaptation to both low (250 Hz) and high (8000 Hz) frequency tones. Subjects with auditory nerve disorders had normal loudness adaptation to low frequency tones; all but one had abnormal adaptation to high frequency tones. Adaptation was both more rapid and of greater magnitude in ribbon synapse than in auditory nerve disorders. Auditory brainstem response measures of adaptation in ribbon synapse disorder showed Wave V to the first click in the train to be abnormal both in latency and amplitude, and these abnormalities increased in magnitude or Wave V was absent to subsequent clicks. In contrast, auditory brainstem responses in four of the five subjects with neural disorders were absent to every click in the train. The fifth subject had normal latency and abnormally reduced amplitude of Wave V to the first click and abnormal or absent responses to subsequent clicks. Thus, dysfunction of both synaptic transmission and auditory neural function can be associated with abnormal loudness adaptation and the magnitude of the adaptation is significantly greater with ribbon synapse than neural disorders.

Objectives/hypothesisTo evaluate a transcanal approach for placement of a stimulating electrode array in the cochlear nerve.Study designProspective cadaveric temporal bone study.MethodsTen human cadaveric temporal bones were dissected. Both a facial recess approach with mastoidectomy and a transcanal approach using the novel technique were performed in each bone. A middle fossa dissection of the internal auditory canal was performed to confirm the position of the electrode in the cochlear nerve.ResultsThe transcanal approach offered a direct approach to the cochlear nerve in all 10 bones. The procedure was quicker than the facial recess approach and did not endanger the facial or chorda tympani nerves. Inspection of the medial end of the internal auditory canal confirmed correct placement of the electrode in the cochlear nerve. In contrast, anatomical constraints, specifically the position of the facial nerve, blocked access to the cochlear nerve by the facial recess approach in three of the specimens to achieve the exposure to place the electrode at a perpendicular angle to the cochlear nerve. Sacrifice of the chorda tympani was necessary in five of the seven bones in which the cochlear nerve could be accessed.ConclusionsThe transcanal approach offers a simpler, safer approach for cochlear nerve implantation compared to the facial recess approach. This approach can be accomplished in less time and avoids the hazards of dissection around the facial nerve. Use of the proposed approach will facilitate development of intraneural stimulation for an improved auditory prosthesis.

Moderate-to-profound sensorineural hearing loss in humans is treatable by electrically stimulating the auditory nerve (AN) with a cochlear implant (CI). In the cochlea, the modiolus presents a porous bony interface between the CI electrode and the AN. New bone growth caused by the presence of the CI electrode or neural degeneration inflicted by ageing or otological diseases might change the effective porosity of the modiolus and, thereby, alter its electrical material properties. Using a volume conductor description of the cochlea, with the aid of a 'mapped conductivity' method and an ad-hoc 'regionally kinetic' equation system, we show that even a slight variation in modiolus porosity or pore distribution can disproportionately affect AN stimulation. Hence, because of porosity changes, an inconsistent CI performance might occur if neural degeneration or new bone growth progress after implantation. Appropriate electrical material properties in accordance with modiolar morphology and pathology should be considered in patient-specific studies. The present first-of-its-kind in-silico study advocates for contextual experimental studies to further explore the utility of modiolus porous morphology in optimising the CI outcome., (© 2024. The Author(s).)

To explore the correlation between the width of the bony cochlear nerve canal (CNC) and long-term auditory rehabilitation after unilateral cochlear implantation (CI) in pediatric patients with congenital deafness and bilateral cochlear nerve canal stenosis (CNCS). A retrospective review was performed on 10 patients with bilateral CNCS and bilateral congenital profound hearing loss who each underwent unilateral cochlear implantation. The width of the CNC was determined on computed tomography (CT) imaging and following CI, auditory and speech performance following CI were graded using categories of auditory performance (CAP), speech intelligibility rating (SIR), and the meaningful auditory integration scale (MAIS) at 24 months following implantation. No correlation was noted between CAP score and CNCS at 24 months post CI ( P > .05). A positive correlation was noted between SIR score and CNC width (ρ = .81, P < .05). Similarly, a positive correlation was noted between MAIS and CNC width (ρ = .71, P < .05). The width of the CNC in patients with CNCS is positively correlated with some long-term auditory and speech outcomes after CI., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Universal Newborn Hearing Screening (NHS) has been a mainstay of immediate post-partum care in the United States since the National Institutes of Health (NIH) released its recommendation for screening in the 1993 Consensus Conference Report.We present the case of a four-year-old female who had passed in-hospital NHS with transient evoked otoacoustic emission (TEOAE) bilaterally, yet presented four years later to the otolaryngology clinic with parental complaints of hearing dysfunction. Audiology evaluation demonstrated profound unilateral sensorineural hearing loss (SNHL) with absent TEOAE. Magnetic resonance imaging (MRI) revealed either absent or severely hypoplastic vestibulocochlear nerve (VCN) on the affected side.This case raises the possibility of initial preservation of outer hair cell function despite cochlear nerve aplasia or deficiency, as evidenced by the presence of TEOAE on NHS. The finding of reduced TEOAE 4 years after initially passing NHS suggests a progression from isolated VCN abnormality to dysfunction of the outer hair cells.

ObjectivesAuditory cortical N100s were examined in ten auditory neuropathy (AN) subjects as objective measures of impaired hearing.MethodsLatencies and amplitudes of N100 in AN to increases of frequency (4-50%) or intensity (4-8 dB) of low (250 Hz) or high (4000 Hz) frequency tones were compared with results from normal-hearing controls. The sites of auditory nerve dysfunction were pre-synaptic (n=3) due to otoferlin mutations causing temperature sensitive deafness, post-synaptic (n=4) affecting other cranial and/or peripheral neuropathies, and undefined (n=3).ResultsAN consistently had N100s only to the largest changes of frequency or intensity whereas controls consistently had N100s to all but the smallest frequency and intensity changes. N100 latency in AN was significantly delayed compared to controls, more so for 250 than for 4000 Hz and more so for changes of intensity compared to frequency. N100 amplitudes to frequency change were significantly reduced in ANs compared to controls, except for pre-synaptic AN in whom amplitudes were greater than controls. N100 latency to frequency change of 250 but not of 4000 Hz was significantly related to speech perception scores.ConclusionsAs a group, AN subjects' N100 potentials were abnormally delayed and smaller, particularly for low frequency. The extent of these abnormalities differed between pre- and post-synaptic forms of the disorder.SignificanceAbnormalities of auditory cortical N100 in AN reflect disorders of both temporal processing (low frequency) and neural adaptation (high frequency). Auditory N100 latency to the low frequency provides an objective measure of the degree of impaired speech perception in AN.

To establish outcomes following cochlear implantation (CI) in patients with postsynaptic auditory neuropathy (AN). Systematic review and narrative synthesis. Databases searched: MEDLINE, PubMed, EMBASE, Web of Science, Cochrane Collection and ClinicalTrials.gov. No limits placed on language or year of publication. Review conducted in accordance with the PRISMA statement. Searches identified 98 studies in total, of which 14 met the inclusion criteria reporting outcomes in 25 patients with at least 28 CIs. Of these, 4 studies focused on Charcot-Marie-Tooth disease (CMT), 3 on Brown- Vialetto-Van-Laere syndrome (BVVL), 2 on Friedreich Ataxia (FRDA), 2 on Syndromic dominant optic atrophy (DOA+), 2 on Cerebellar ataxia - areflexia - pes cavus - optic atrophy - sensorineural hearing loss (CAPOS) syndrome, and 1 on Deafness-dystonia-optic neuronopathy (DDON) syndrome. All studies were Oxford Centre for Evidence Based Medicine (OCEBM) grade IV. Overall trend was towards good post-CI outcomes with 22 of the total 25 patients displaying modest to significant benefit. Hearing outcomes following CI in postsynaptic ANs are variable but generally good with patients showing improvements in hearing thresholds and speech perception. In the future, development of a clearer stratification system into pre, post, and central AN would have clinical and academic benefits. Further research is required to understand AN pathophysiology and develop better diagnostic tools for more accurate identification of lesion sites. Multicenter longitudinal studies with standardized comprehensive outcome measures including health-related quality of life data will be key in establishing a better understanding of short and long-term post-CI outcomes. [ABSTRACT FROM AUTHOR]

OBJECTIVES: This study aimed to report the auditory performance in children with cochleovestibular malformation (CVM)/cochlear nerve deficiency (CND) who were implanted early at the Universiti Kebangsaan Malaysia Medical Centre, using Categorical Auditory Performance (CAP)-II score and Speech Intelligibility Rating (SIR) scales, and to compare the outcome of their matched counterparts. MATERIALS and METHODS: A total of 14 children with CVM/CND with unilateral cochlear implant (CI) implanted before the age of 4 years old were matched and compared with 14 children with normal inner ear structures. Their improvement in auditory performance was evaluated twice using CAP-II score and SIR scales at 6-month intervals, with the baseline evaluation done at least 6 months after implantation. RESULTS: The average age of implantation was 31±8 and 33±7 months for the control group and the case (CVM/CND) group, respectively. Overall, there were no significant differences in outcome when comparing the entire cohort of case subjects and their matched control subjects in this study. However, the improvement in CAP-II scores and SIR scales among the case subjects in between the first and second evaluations was statistically significant (p=0.040 and p=0.034, respectively). With longer duration of CI usage, children with CVM/CND showed significant speech perception outcome evident by their SIR scales (p=0.011). CONCLUSION: Children with radiographically malformed inner ear structures who were implanted before the age of 4 years have comparable performance to their matched counterparts, evident by their similar improvement of CAP-II scores and SIR scales over time. Hence, this group of children benefited from cochlear implantation. [ABSTRACT FROM AUTHOR]

Otoferlin is involved in neurotransmitter release at the synapse between inner hair cells (IHCs) and auditory nerve fibres, and mutations in the OTOF gene result in severe to profound hearing loss. Abnormal sound-evoked cochlear potentials were recorded with transtympanic electrocochleography from four children with otoferlin (OTOF) mutations to evaluate physiological effects in humans of abnormal neurotransmitter release from IHCs. The subjects were profoundly deaf with absent auditory brainstem responses and preserved otoacoustic emissions consistent with auditory neuropathy. Two children were compound heterozygotes for mutations c.2732_2735dupAGCT and p.Ala964Glu; one subject was homozygous for mutation p.Phe1795Cys, and one was compound heterozygote for two novel mutations c.1609delG in exon 16 and c.1966delC in exon 18. Cochlear potentials evoked by clicks from 60 to 120 dB peak equivalent sound pressure level were compared to recordings obtained from 16 normally hearing children. Cochlear microphonic (CM) was recorded with normal amplitudes from all but one ear. After cancelling CM, cochlear potentials were of negative polarity with reduced amplitude and prolonged duration compared to controls. These cochlear potentials were recorded as low as 50-90 dB below behavioural thresholds in contrast to the close correlation in controls between cochlear potentials and behavioural threshold. Summating potential was identified in five out of eight ears with normal latency whilst auditory nerve compound action potentials were either absent or of low amplitude. Stimulation at high rates reduced amplitude and duration of the prolonged potentials, consistent with neural generation. This study suggests that mechano-electrical transduction and cochlear amplification are normal in patients with OTOF mutations. The low-amplitude prolonged negative potentials are consistent with decreased neurotransmitter release resulting in abnormal dendritic activation and impairment of auditory nerve firing.

Autosomal dominant optic atrophy (DOA) is a retinal neuronal degenerative disease characterized by a progressive bilateral visual loss. We report on two affected members of a family with dominantly inherited neuropathy of both optic and auditory nerves expressed by impaired visual acuity, moderate pure tone hearing loss, and marked loss of speech perception. We investigated cochlear abnormalities accompanying the hearing loss and the effects of cochlear implantation. We sequenced OPA1 gene and recorded cochlear receptor and neural potentials before cochlear implantation. Genetic analysis identified R445H mutation in OPA1 gene. Audiological studies showed preserved cochlear receptor outer hair cell activities (otoacoustic emissions) and absent or abnormally delayed auditory brainstem responses (ABRs). Trans-tympanic electrocochleography (ECochG) showed prolonged low amplitude negative potentials without auditory nerve compound action potentials. The latency of onset of the cochlear potentials was within the normal range found for inner hair cell summating receptor potentials. The duration of the negative potential was reduced to normal during rapid stimulation consistent with adaptation of neural sources generating prolonged cochlear potentials. Both subjects had cochlear implants placed with restoration of hearing thresholds, speech perception, and synchronous activity in auditory brainstem pathways. The results suggest that deafness accompanying this OPA1 mutation is due to altered function of terminal unmyelinated portions of auditory nerve. Electrical stimulation of the cochlea activated proximal myelinated portions of auditory nerve to restore hearing.

ObjectiveAuditory temporal processes in quiet are impaired in auditory neuropathy (AN) similar to normal hearing subjects tested in noise. N100 latencies were measured from AN subjects at several tone intensities in quiet and noise for comparison with a group of normal hearing individuals.MethodsSubjects were tested with brief 100 ms tones (1.0 kHz, 100-40 dB SPL) in quiet and in continuous noise (90 dB SPL). N100 latency and amplitude were analyzed as a function of signal intensity and audibility.ResultsN100 latency in AN in quiet was delayed and amplitude was reduced compared to the normal group; the extent of latency delay was related to psychoacoustic measures of gap detection threshold and speech recognition scores, but not to audibility. Noise in normal hearing subjects was accompanied by N100 latency delays and amplitude reductions paralleling those found in AN tested in quiet. Additional N100 latency delays and amplitude reductions occurred in AN with noise.ConclusionsN100 latency to tones and performance on auditory temporal tasks were related in AN subjects. Noise masking in normal hearing subjects affected N100 latency to resemble AN in quiet.SignificanceN100 latency to tones may serve as an objective measure of the efficiency of auditory temporal processes.

ObjectiveTranstympanic electrocochleography (ECochG) was recorded bilaterally in children and adults with auditory neuropathy (AN) to evaluate receptor and neural generators.MethodsTest stimuli were clicks from 60 to 120dB p.e. SPL. Measures obtained from eight AN subjects were compared to 16 normally hearing children.ResultsReceptor cochlear microphonics (CMs) in AN were of normal or enhanced amplitude. Neural compound action potentials (CAPs) and receptor summating potentials (SPs) were identified in five AN ears. ECochG potentials in those ears without CAPs were of negative polarity and of normal or prolonged duration. We used adaptation to rapid stimulus rates to distinguish whether the generators of the negative potentials were of neural or receptor origin. Adaptation in controls resulted in amplitude reduction of CAP twice that of SP without affecting the duration of ECochG potentials. In seven AN ears without CAP and with prolonged negative potential, adaptation was accompanied by reduction of both amplitude and duration of the negative potential to control values consistent with neural generation. In four ears without CAP and with normal duration potentials, adaptation was without effect consistent with receptor generation. In five AN ears with CAP, there was reduction in amplitude of CAP and SP as controls but with a significant decrease in response duration.ConclusionsThree patterns of cochlear potentials were identified in AN: (1) presence of receptor SP without CAP consistent with pre-synaptic disorder of inner hair cells; (2) presence of both SP and CAP consistent with post-synaptic disorder of proximal auditory nerve; (3) presence of prolonged neural potentials without a CAP consistent with post-synaptic disorder of nerve terminals.SignificanceCochlear potential measures may identify pre- and post-synaptic disorders of inner hair cells and auditory nerves in AN.

The clawed frog Xenopus laevis produces vocalizations consisting of distinct patterns of clicks. This study provides the first description of spontaneous, pure-tone and communication-signal evoked discharge properties of auditory nerve (n.VIII) fibers and dorsal medullary nucleus (DMN) cells in an obligatorily aquatic anuran. Responses of 297 n.VIII and 253 DMN units are analyzed for spontaneous rates (SR), frequency tuning, rate-intensity functions, and firing rate adaptation, with a view to how these basic characteristics shape responses to recorded call stimuli. Response properties generally resemble those in partially terrestrial anurans. Broad tuning exists across characteristic frequencies (CFs). Threshold minima are -101 dB re 1 mm/s at 675 Hz; -87 dB at 1,600 Hz; and -61 dB at 3,000 Hz (-90, -77, and -44 dB re 1 Pa, respectively), paralleling the peak frequency of vocalizations at 1.2-1.6 kHz with approximately 500 Hz in 3 dB bandwidth. SRs range from 0 to 80 (n.VIII) and 0 to 73 spikes/s (DMN). Nerve and DMN units of all CFs follow click rates in natural calls, < or =67 clicks/s and faster. Units encode clicks with a single spike, double spikes, or bursts. Spike times correlate closely with click envelopes. No temporal filtering for communicative click rates occurs in either n.VIII or the DMN.

We have studied 72 members belonging to a large kindred with a hearing disorder inherited in an autosomal dominant pattern. We used audiological, physiological, and psychoacoustic measures to characterize the hearing disorders. The initial phenotypic features of the hearing loss are of an auditory neuropathy (AN) with abnormal auditory nerve and brainstem responses (ABRs) and normal outer hair cell functions [otoacoustic emissions (OAEs) and cochlear microphonics (CMs)]. Psychoacoustic studies revealed profound abnormalities of auditory temporal processes (gap detection, amplitude modulation detection, speech discrimination) and frequency processes (difference limens) beyond that seen in hearing impairment accompanying cochlear sensory disorders. The hearing loss progresses over 10-20 years to also involve outer hair cells, producing a profound sensorineural hearing loss with absent ABRs and OAEs. Affected family members do not have evidence of other cranial or peripheral neuropathies. There was a marked improvement of auditory functions in three affected family members studied after cochlear implantation with return of electrically evoked auditory brainstem responses (EABRs), auditory temporal processes, and speech recognition. These findings are compatible with a distal auditory nerve disorder affecting one or all of the components in the auditory periphery including terminal auditory nerve dendrites, inner hair cells, and the synapses between inner hair cells and auditory nerve. There is relative sparing of auditory ganglion cells and their axons.

Non-invasive electrophysiological measures, such as auditory evoked potentials (AEPs), play a crucial role in diagnosing auditory pathology. However, the relationship between AEP morphology and cochlear degeneration remains complex and not well understood. Dau [J. Acoust. Soc. Am. 113, 936-950 (2003)] proposed a computational framework for modeling AEPs that utilized a nonlinear auditory-nerve (AN) model followed by a linear unitary response function. While the model captured some important features of the measured AEPs, it also exhibited several discrepancies in response patterns compared to the actual measurements. In this study, an enhanced AEP modeling framework is presented, incorporating an improved AN model, and the conclusions from the original study were reevaluated. Simulation results with transient and sustained stimuli demonstrated accurate auditory brainstem responses (ABRs) and frequency-following responses (FFRs) as a function of stimulation level, although wave-V latencies remained too short, similar to the original study. When compared to physiological responses in animals, the revised model framework showed a more accurate balance between the contributions of auditory-nerve fibers (ANFs) at on- and off-frequency regions to the predicted FFRs. These findings emphasize the importance of cochlear processing in brainstem potentials. This framework may provide a valuable tool for assessing human AN models and simulating AEPs for various subtypes of peripheral pathologies, offering opportunities for research and clinical applications., (© 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).)