Academic literature on the topic 'Cochlear nerve pathologies'

This is a case report of a 53-yr-old female who experienced sudden sensorineural hearing loss (SSNHL) accompanied by roaring tinnitus in her right ear. The patient’s hearing partially improved in the low frequencies in response to intratympanic injections. Given that her hearing loss did not improve further, the patient was fitted with a hearing aid to mask the tinnitus and restore a sense of balance between the two ears. Approximately 9 mo postonset of the SSNHL, a complete spontaneous recovery of hearing occurred. Such a delayed and complete recovery is highly unusual.This case highlights that the spontaneous recovery in hearing indicates that the pathological cause for the SSNHL involved a process that was capable of repair or regeneration, thus ruling out pathologies related to cochlear hair cell destruction or nerve fiber loss. This leaves a possibility that the event causing the onset of the SSNHL resulted in a disruption of the ion homeostatic properties of the cochlea via the production of the endocochlear potential.

Parasagittal surface-coil magnetic resonance imaging of the internal auditory canal and the inner ear was performed. We used T2-weighted fast spin-echo sequences to visualize the inner ear and the individual nerves in the internal auditory canal with high contrast in a short acquisition time. Computer-assisted quantitative measurement of the nerves was performed to estimate the cross-sectional areas and the diameters of the nerves. The average diameters of the facial nerve, the cochlear nerve, and the vestibular nerve of normal-hearing individuals were, respectively, 1.1 ± 0.2 mm (mean ± SD), 1.2 ± 0.2 mm, and 1.5 ± 0.2 mm. In the cerebellopontine angle, the average diameter of the eighth nerve was 1.8 ± 0.2 mm. Two patients with unilateral and bilateral hearing loss were also presented. In the patient with unilateral deafness, the cochlear nerve of the diseased side was not identified and the eighth cranial nerve diameter was smaller than that of the normal side. In the patient with bilateral deafness, fibrosis of the inner ear and atrophy of the eighth nerve were demonstrated in the ear with posttraumatic deafness. The present method may represent a new approach to the assessment of pathologic processes involving the inner ear and the nerves in the internal auditory canal.

Objective. The degeneration of hair cells and spiral ganglion neurons (SGNs) is an important pathologic process in the development of sensorineural hearing loss. In a murine model, predictable and reproducible damage to SGNs occurs through the application of ouabain to the round window. Recent evidence has shown that the chemokine stromal cell–derived factor-1 (SDF-1) is a potent chemoattractant of hematopoietic stem cells (HSCs) and provides trophic support to injured tissues during development and maturation. The hypothesis for the current study is that expression of SDF-1 plays an important role in protecting SGNs and preventing further degeneration in the setting of cochlear injury. Study Design. Prospective, controlled. Setting. Academic research laboratory. Subject and Methods. Auditory brainstem response (ABR) and the expression of SDF-1 mRNA and protein were examined 1, 3, 7, 14, and 30 days after application of ouabain in 35 adult mice. Results. Following ouabain application, real-time reverse-transcription polymerase chain reaction for SDF demonstrates increased mRNA expression following ouabain injury in nontransplanted mice. A significant increase in SDF protein expression was also observed using immunolabeling techniques and Western blot analysis. Conclusions. SDF-1 expression is increased in the auditory nerve following cochlear injury. Further knowledge about the cochlear microenvironment, including SDF-1, is critical to maximizing HSC engraftment in the injured cochlea and providing a therapeutic option for sensorineural hearing loss.

AbstractA case is reported in which a Nucleus 22 channel intracochlear implant was used to treat a deaf Hungarian woman (aged 37 years) with a 34-year history of grand mal (GM) epilepsy maintained on carbamazepinediazepam combination therapy who had not benefited from conventional hearing aids. Pre-operative electrical stimulation of the acoustic nerve, however, exhibited a good nerve function with no evidence of abnormal waveforms in the electroencephalogram (EEG). Successful intracochlear insertion of the 22 electrode resulted in a 40 dB hearing improvement at frequencies 250–2000 Hz in the implanted ear with no signs of pathologic wave activity at either the previously recognized epileptic focus (fronto-precentral region) or indeed, in other regions of the brain at use of the implant. We conclude that intracochlear implantation per se is not a hazardous intervention in patients with fronto-precentral epileptic foci.

We found a selective loss of vestibular hair cells in a patient followed for more than 10 years with imbalance and oscillopsia due to idiopathic progressive loss of vestibular function. Hearing function and cochlear hair cells were normal. The vestibulo-ocular reflex (VOR) gain at high frequencies was relatively maintained despite marked shortening of the dominant VOR time constant (to less than 500 ms). Ultrastructural examination of remaining hair cells showed mitochondrial abnormalities. The ultrashort VOR time constant probably resulted from changes in firing patterns of the primary afferent nerves due to loss of hair cells and impaired energy metabolism in remaining hair cells.

Tinnitus is not a single disease but a group of different diseases with different pathologies and therefore different treatments. Regarding tinnitus as a single disease is hampering progress in understanding of the pathophysiology of tinnitus and perhaps, more importantly, it is a serious obstacle in development of effective treatments for tinnitus. Subjective tinnitus is a phantom sound that takes many different forms and has similarities with chronic neuropathic pain. The pathology may be in the cochlea, in the auditory nerve, or, most commonly, in the brain. Like chronic neuropathic pain tinnitus is not life threatening but influences many normal functions such as sleep and the ability to concentrate on work. Some forms of chronic tinnitus have two components, a (phantom) sound and a component that may best be described as suffering or distress. The pathology of these two components may be different and the treatment that is most effective may be different for these two components. The most common form of treatment of tinnitus is pharmacological agents and behavioral treatment combined with sound therapy. Less common treatments are hypnosis and acupuncture. Various forms of neuromodulation are becoming in use in an attempt to reverse maladaptive plastic changes in the brain.

Objectives: This is a qualitative study to explore the utility of gray-scale inversion or the “invert” function of high-resolution computed tomography (HRCT) scans in the diagnosis of temporal bone anatomy and pathology. Methods: This is a case series describing an innovative application of an existing image processing tool to visualize temporal bone anatomy and pathology. Illustrative patients at a tertiary referral center with otologic symptoms and findings leading to HRCT scans of the temporal bone were included. Diagnostic HRCT scans were evaluated utilizing the gray-scale inversion function (invert function). Results: Nine illustrative cases which demonstrate conditions such as persistent stapedial artery, membranous stapes footplate, total ossicular prosthesis migration into the vestibule, third window syndrome such as superior semicircular canal dehiscence (SSCD) and cochlea-facial nerve dehiscence, otosclerosis, and ossicular chain discontinuity are included. The enhanced visualization was confirmed surgically in 3 cases, and 1 had physiological confirmation using cervical vestibular evoked myogenic potentials (cVEMP). Conclusions: Gray-scale inversion can be used to improve visualization of temporal bone anatomy and pathologic changes when diagnoses are in doubt. The invert function is a useful adjunct in the armamentarium of both radiologists and otologists when evaluating HRCT of the temporal bone.

<p class="abstract"><strong>Background:</strong> Cochlear synaptic tinnitus (CST), also referred to as sensorineural type III tinnitus, is a type of transformation tinnitus, resulting due to aberrant signal transduction between Inner hair cells and afferent nerve fibres owing to excessive and pathologic glutamate release and subsequent spontaneous receptor depolarization (NMDA and AMPA receptors). Of the various pharmacologic agents used for treatment for CST, <em>Gingko biloba</em> and Caroverine have stood the test of time.</p><p class="abstract"><strong>Methods:</strong> A total 48 selected patients of CST, otherwise free from any medical or surgical co-morbidity, were included in the study and divided randomly in two groups, one group receiving oral formulation of Caroverine and the other group receiving oral <em>Gingko biloba</em> in appropriate doses. Both the groups were followed up for 12 weeks. Treatment outcomes were measured in terms of improvement in subjective symptoms (tinnitus grading) and psycho-acoustic measure (tinnitus matching).</p><p class="abstract"><strong>Results:</strong> Although oral caroverine yielded promising results in the initial month of treatment in terms of improved tinnitus matching, long term effect was found to be dissatisfying. Oral <em>Gingko biloba</em>, at the completion of 12 weeks of therapy was found to be more effective in terms of improvement of mean tinnitus grading and matching (p&lt;0.05). Side effects of the test drugs were not noted in either group.</p><p class="abstract"><strong>Conclusions:</strong> <em>Gingko biloba</em> is thus found to be more effective treatment modality for CST for long term basis and is also readily available in the market, cost effective and free of side effects as well.</p>

AbstractA fundamental property of mammalian hearing is the conversion of sound pressure into a frequency-specific place of maximum vibration along the cochlear length, thereby creating a tonotopic map. The tonotopic map makes possible systematic frequency tuning across auditory-nerve fibers, which enables the brain to use pitch to separate sounds from different environmental sources and process the speech and music that connects us to people and the world. Sometimes a tone has a different pitch in the left and right ears, a perceptual anomaly known as diplacusis. Diplacusis has been attributed to a change in the cochlear frequency-place map, but the hypothesized abnormal cochlear map has never been demonstrated. Here we assess cochlear frequency-place maps in guinea-pig ears with experimentally-induced endolymphatic hydrops, a hallmark of Ménière’s disease. Our findings are consistent with the hypothesis that diplacusis is due to an altered cochlear map. Map changes can lead to altered pitch, but the size of the pitch change is also affected by neural synchrony. Our data show that the cochlear frequency-place map is not fixed but can be altered by endolymphatic hydrops. Map changes should be considered in assessing hearing pathologies and treatments.

[Truncated abstract] The present study investigated whether any of the characteristics of the compound action potential (CAP) waveform or the spectrum of the neural noise (SNN) recorded from the cochlea, could be used to examine abnormal spike generation in the type I primary afferent neurones, possibly due to pathologies leading to abnormal hearing such as tinnitus or tone decay. It was initially hypothesised that the CAP waveform and SNN contained components produced by the local action currents generated at the peripheral ends of the type I primary afferent neurones, and that changes in these local action currents occurred due to changes in the membrane potential of these neurones. It was further hypothesised that the lateral olivo-cochlear system (LOCS) efferent neurones regulate the membrane potential of the primary afferent dendrites to maintain normal action potential generation, where instability in the membrane potential might lead to abnormal primary afferent firing, and possibly one form of tinnitus. We had hoped that the activity of the LOCS efferent neurones could be observed through secondary changes in the CAP waveform and SNN, resulting from changes in the membrane potential of the primary afferent neurones. The origins of the neural activity generating the CAP waveform and SNN peaks, and the effects of the LOCS on the CAP and SNN were experimentally investigated in guinea pigs using lesions in the auditory system, transient ischemia and asphyxia, focal and systemic temperature changes, and pharmacological manipulations of different regions along the auditory pathway. ... Therefore, the CAP and SNN are altered by changes in the propagation of the action potential along the primary afferent neurones, by changes in the morphology of the tissues surrounding the cochlear nerve, and by changes in the time course of the action currents. If the CAP waveform is not altered, the amplitude of the 1kHz speak in the spontaneous SNN can be used as an objective measure of the spontaneous firing rate of the cochlear neurones. However, because the SNN contains a complex mixture of neural activity from all cochlear neurones, and the amplitude of the spontaneous SNN is variable, it would be difficult to use the spontaneous SNN alone as a differential diagnostic test of cochlear nerve pathologies. To record extratympanic electrocochleography (ET ECochG) from humans, a custom-designed, inexpensive, low-noise, optically isolated biological amplifier was built. Furthermore, a custom-designed extratympanic active electrode and ear canal indifferent electrode were designed, which increased the signal-to-noise ratio of the ECochG recording by a factor of 2, decreasing the overall recording time by 75%. The human and guinea pig CAP waveforms recorded in the present study appeared similar, suggesting that the origins of the human and guinea pig CAP waveforms were the same, and that experimental manipulations of the guinea pig CAP waveform can be used to diagnose the cause of abnormal human ECochG waveforms in cases of cochlear nerve pathologies.