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Results for “Cochlear Nerve”

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PubMed1978

Pathologic features of the cochlear nerve in profound deafness.

Cochlear nerves transected in the internal meatus were studied in six totally deaf ears and in one ear with profound deafness. In five ears deafness had followed surgical procedures in the oval window, in one it was the result of a mumps infection, and one was probably due to a virus infection or a vascular lesion. In four cases there was no great reduction in the nerve fiber population and the ultrastructure appeared normal. In three nerves there was a reduction in the number of nerve fibers, interfibrillar fibrosis, and disorganized material or extensive degenerative changes in the myelin sheaths. In all specimens artificial myelin changes were seen that apparently resulted from manipulation of the specimens at removal. Analysis of these cochlear nerves suggests that retrograde degeneration after severe cochlear insults may not be as frequent as has been thought on the basis of animal studies.

Adult↗

PubMed1998

Direct cochlear nerve monitoring: first report on a new atraumatic, self-retaining electrode.

OBJECTIVE: To assess the efficacy and safety of a new atraumatic, self-retaining cranial nerve electrode for direct cochlear nerve monitoring during cerebellopontine angle surgery. STUDY DESIGN: Prospective clinical investigation. SETTING: The Skull Base Surgery Center at Kaiser Permanente, San Diego, a tertiary referral center for neurotologic and skull-base surgery within Southern California Permanente Medical Group. PATIENTS: Eighteen patients, with aidable preoperative hearing, underwent direct cochlear nerve monitoring with this new electrode during cerebellopontine angle surgery for a variety of diagnoses. METHODS: Intraoperative observations of cochlear nerve action potential amplitude and latency were recorded. Preoperative and 1-month postoperative audiograms were compared to assess the degree of hearing preservation. Postoperative facial nerve function was assessed using the House-Brackmann method. RESULTS: Good auditory function was preserved in four of eight acoustic tumors, with poor hearing preserved in two additional patients. Good auditory function was preserved in the remaining ten patients. Cochlear nerve action potential amplitudes between 5 and 70 microV were recorded. Postoperative facial nerve function was House-Brackmann class I-II in all 18 patients. CONCLUSION: The authors find this new electrode to be safe and effective for monitoring cochlear nerve function during cerebellopontine angle surgery.

Cerebellopontine Angle↗

PubMed2006

Auditory neuropathy characteristics in children with cochlear nerve deficiency.

OBJECTIVE: To describe a group of children exhibiting electrophysiologic responses characteristic of auditory neuropathy (AN) who were subsequently identified as having absent or small cochlear nerves (i.e., cochlear nerve deficiency). DESIGN: A retrospective review of the clinical records, audiological testing results, and magnetic resonance imaging (MRI) studies. Fifty-one of 65 children with AN characteristics on auditory brain stem response (ABR) testing had MRI available for review. Nine (18%) of these 51 children with ABR characteristic of AN have been identified as having small (N = 2; 4%) or absent (N = 7; 14%) cochlear nerves on MRI. RESULTS: Of the nine children with cochlear nerve deficiency, five (56%) were affected unilaterally and four (44%) bilaterally. Eight of nine presented after failing a newborn infant hearing screening, whereas one presented at 3 yr of age. On diagnostic ABR testing, all 9 children (9 of 13 affected ears; 69%) had evidence of a cochlear microphonic (CM) and absent neural responses in at least one ear. In the unilateral cases, AN characteristics were detected in all affected ears. In bilateral cases, at least one of the ears in each child demonstrated the AN phenotype, whereas the contralateral ear had no CM identified. Only one ear with cochlear nerve deficiency had present otoacoustic emissions as measured by distortion-product otoacoustic emissions. In children with appropriate available behavioral testing results, all ears without cochlear nerves were identified as having a profound hearing loss. Only 4 (31%) of the 13 ears with cochlear nerve deficiency had a small internal auditory canal on MRI. CONCLUSIONS: Children with cochlear nerve deficiency can present with electrophysiologic evidence of AN. These children frequently refer on newborn screening examinations that use ABR-based testing methods. Similar to other causes of AN, diagnostic ABR testing will show a CM with absent neural responses. Given that 9 (18%) of 51 children with available MRI and electrophysiologic characteristics of AN in our program have been identified as having cochlear nerve deficiency makes this a relatively common diagnosis. These findings suggest that MRI is indicated for all children diagnosed with AN. Moreover, electrophysiologic evidence of unilateral AN in association with a profound hearing loss should make the clinician highly suspicious for this problem. Although children with cochlear nerve deficiency who have a small nerve may benefit from cochlear implantation or amplification, these interventions are obviously contraindicated in children with completely absent cochlear nerves.

Audiometry, Pure-Tone↗

PubMed2003

The sciatic nerve of the toad Xenopus laevis as a physiological model of the human cochlear nerve.

The response of single fibres of the human cochlear nerve to electrical stimulation by a cochlear implant has previously been inferred from the response of the cochlear nerve in other mammals. These experiments are hindered by stimulus artefact and the range of stimulus currents used is therefore much less than the perceptual dynamic range (from threshold to discomfort) of human subjects. We have investigated use of the sciatic nerve of the toad Xenopus laevis as a convenient physiological model of the human cochlear nerve. Use of this completely dissected nerve reduces the problems of stimulus artefact whilst maintaining the advantages of a physiological preparation. The validity of the model was assessed by measuring the refractory periods, excitation time-constant, and relative spread of single fibres using microelectrode recording. We have also investigated the response of nerve fibres to sinusoidal stimulation. Based on these measurements, we propose that the sciatic nerve may be a suitable model of the human cochlear nerve if the timescales of stimuli are decreased by a factor of about five to compensate for the slower dynamics of the sciatic nerve and if noise is added to the stimuli to compensate for the lower internal noise of sciatic nerve fibres.

Animals↗

PubMed1994

Computer-assisted assessment of cochlear nerve fibers.

Quantitative assessment of cochlear nerve fibers, with statistical analysis of histologic specimens, is facilitated by the application of computer image processing techniques. Three algorithms, developed for the evaluation of cochlear sections, are presented, MANUAL, AIDED, and AUTO, in order of increasing degree of automation and decreasing requirement for operator intervention. All three algorithms demonstrate high accuracy and consistency in identifying cochlear nerve fibers and quickly provide statistics regarding the target nerve fiber population. These algorithms have potential utility in the study of cochlear nerve pathologic alterations, as for example, with intracochlear electrical stimulation.

Animals↗

PubMed1990

Delayed spontaneous return of hearing after acoustic tumor surgery: evidence for cochlear nerve conduction block.

Unlike the eventual resolution of facial paralysis in most patients with intact facial nerves, delayed hearing return after acoustic tumor resection is rare. This discrepancy in recovery has been ascribed to the inherent resilience of the facial nerve (a special visceral efferent nerve) to injury versus the cochlear nerve (a special somatic afferent nerve). In the presence of an intact cochlear nerve, hearing loss has been attributed to transection or spasm of the internal auditory artery or to direct mechanical trauma to the cochlear nerve during manipulation of the tumor. The possibility of a reversible conduction block in the cochlear nerve has not been considered. A review of three instances of delayed spontaneous hearing recovery several months after acoustic tumor resection suggests that a conduction block phenomenon can exist. This report describes the pathophysiology and the possible intraoperative predisposing features of this condition.

Adult↗

PubMed1982

Functional synapse elimination in the developing avian cochlear nucleus with simultaneous reduction in cochlear nerve axon branching.

We studied the chick auditory system to determine whether there is a normal developmental reduction in the number of cochlear nerve axons innervating individual cochlear nucleus (nucleus magnocellularis, NM) neurons. We also examined the preterminal branching patterns of cochlear nerve axons during development. The number of cochlear nerve axons innervating individual NM neurons was estimated by counting the increments in the postsynaptic response as the intensity of cochlear nerve electrical stimulation was varied gradually; this number fell from a mean of 4.0 on embryonic day 13 (E13) to a mean of 2.2 on E17 and E18 and the 4th day after hatching. This highly reliable decline in functional convergence was accompanied by a decrease in the number of preterminal branches of cochlear nerve fibers innervating the NM. On E13 and E14, most axons stained by iontophoretic injections of horseradish peroxidase showed two distinct preterminal branches in the NM. By E17 and E18 and thereafter, cochlear nerve axons were unbranched and terminated with a characteristic single large calycine ending in the NM. There are about twice as many cochlear nerve axons as neurons in the NM and the number of fibers in the nerve appears to decline only slightly between E13 and E17. The 50% decline in the number of cochlear nerve axons making functional synapses on individual NM neurons therefore is associated principally with the concurrent elimination of cochlear nerve axon branching in the NM.

Animals↗

PubMed2002

Imaging findings of cochlear nerve deficiency.

BACKGROUND AND PURPOSE: High-resolution T2-weighted fast spin-echo MR imaging provides excellent depiction of the cisternal and intracanalicular segments of the vestibulocochlear and facial nerves. Absence or reduction in caliber of the cochlear nerve (deficiency) has been described in association with congenital sensorineural hearing loss (SNHL). Depiction of cochlear nerve integrity may be important for diagnosis and management of SNHL. METHODS: We retrospectively reviewed high-resolution T2-weighted fast spin-echo MR images of 22 patients examined for SNHL who had deficiency of the cochlear nerve. Images were evaluated for the presence and comparative size of the component nerves (facial, cochlear, superior vestibular, and inferior vestibular nerves), relative size of the internal auditory canal (IAC), and any associated inner ear abnormalities. The clinical history, results of the clinical examination, and audiometric findings were reviewed for each patient. RESULTS: Deficiency of the cochlear nerve was observed in 12 patients with congenital SNHL and in 10 patients with acquired SNHL. Hypoplasia of the IAC was observed in association with congenital deficiency of the cochlear nerve in 11 of 12 patients. Deficiency of the cochlear nerve was observed in association with acoustic schwannoma in two cases and with acquired labyrinthine abnormalities in seven cases. Hypoplasia of the IAC was not observed in association with acquired SNHL. CONCLUSION: Deficiency of the cochlear nerve can be shown by high-resolution T2-weighted fast spin-echo MR imaging. Deficiency may be observed in association with congenital or acquired SNHL and may be important in the assessment of patients for cochlear implantation. Hypoplasia of the IAC is an indicator of congenital cochlear nerve deficiency.

Adult↗

PubMed1980

The cochlear nerve in Meniere's disease.

Cochlear nerves of 11 patients with advanced Meniere's disease were studied by light and electron microscopy. All the nerves appeared normal on light microscopy. In cross sections, the density of myelinated nerve fibers was approximately 20,000 fibers per square millimeter in most cases. In two cases, the density was reduced, about 14,000/sq mm. No correlation was found between the age of patients or the duration of the disease and the density of myelinated nerve fibers. On electron microscopy, there were several features that suggested primary axonal degeneration or segmental demyelination in the cochlear nerve.

Age Factors↗

PubMed2006

An evaluation of the risk of cerebrospinal fluid leakage as a function of the surgical approach to the cochlear nerve.

OBJECTIVE: Direct implantation into the cochlear nerve can bypass the potential limitations of conventional cochlear implants. Implantable electrical arrays increase the number of stimulation sites, broaden frequency selectivity, require less activating current, and are not dependent on cochlear anatomy. Cochlear nerve implantation demands a unique surgical exposure to the modiolus. This study comprises an assessment of the risk of generating an intraoperative cerebrospinal fluid (CSF) leak using this approach. METHODS: Five fresh cadavers were obtained for dissection. Using dyed normal saline as an indicator, the central nervous system was pressurized to physiological parameters. Surgical approaches to the cochlear nerve were initiated. Leakage of indicator fluid for each approach was quantitatively and qualitatively assessed. Indicator dye in the surgical field was considered a CSF breech. Indicator fluid was collected and quantified. RESULTS: Eighty percent of the surgical approaches caused quantifiable leaks with rates ranging from 0.1 mL/minute to 6 mL/minute. For directly implanted microarrays, the utilization of a modified facial recess approach with cochleostomy and modiolar drillout carries significant risk for generating a CSF leak during the procedure.

Aged, 80 and over↗

PubMed1988

Surgical management of acoustic neuromas during the last five years. Part II: Results for facial and cochlear nerve function.

Postoperative facial and cochlear nerve function in 83 consecutive patients with acoustic neuromas, who were undergoing their initial surgical procedure during 1980-1984, have been examined. The facial nerve was preserved in anatomic continuity in 71% of cases. Various nerve grafting procedures were used when the facial nerve was divided; the most common of these was a faciohypoglossal anastomosis, which was performed in 20 cases. The facial and cochlear nerves were anatomically preserved in 30.1% of all patients having their initial surgical procedure. Good speech discrimination was preserved in four patients, whereas more crude hearing was preserved in six other patients.

Adolescent↗

PubMed1988

Changes with age in the morphology of the cochlear nerve in rats: light microscopy.

Cochlear nerve morphology was examined in a series of rats ranging in age from young adulthood to advanced age in order to assess the extent of fiber loss and the nature of degenerative changes with age. The animals were perfused via the aorta with mixed aldehydes. Blocks including the cochlear nerves were removed, embedded in Araldite, and sectioned in a plane transverse to the longitudinal axis of the nerve. Analysis of the material included counts of normal and degenerating fibers and of glial cells, maps of fiber packing densities, and measurements of the cross-sectional area of the nerve. The median number of normal fibers in the young adult animals (2-3 months) was 21,218. This number was reduced by 21% at 26.5 months and by 24% in the oldest group (35-36 months). The number of degenerating myelin sheaths was first seen to be significantly increased at 6 months, reached a peak at 26.5 months, and declined at 35-36 months. There was an age-related increase in the cross-sectional area of the nerve, amounting to about 60% at 26.5 months and to about 50% at 35-36 months. Fiber packing density decreased evenly with age over the area of the nerve. The increased cross-sectional area and decreased fiber packing density appeared to be related to increases in the thickness of myelin sheaths and in the area occupied by interneural elements.

Aging↗

PubMed2001

Aplasia of the cochlear nerve: a temporal bone study.

OBJECTIVE: The purpose of this study was to evaluate the temporal bone findings in individuals with cochlear nerve aplasia. STUDY DESIGN: Retrospective case review. METHODS: Two individuals with unilateral profound deafness caused by aplasia of the cochlear nerve were identified. The temporal bones were processed, and the cochlear elements were quantified. RESULTS: Histopathologic study of the temporal bones from these individuals demonstrate that a fully formed cochlea and normal-appearing organ of Corti can occur in the absence of the spiral ganglion and cochlear nerve. Cochlear nerve aplasia can occur in both a narrow or a normal-sized internal auditory canal. CONCLUSION: These findings suggest that the development of the cochlea and organ of Corti are not dependent on the presence of the cochlear nerve and spiral ganglion. The entity of cochlear nerve aplasia in the presence of a normally formed cochlea must be considered when evaluating individuals as candidates for cochlear implantation.

Adult↗

PubMed1985

Light and electron microscopic investigation of cochlear nerve specimens from profoundly deaf patients.

Surgical specimens of cochlear nerves from patients suffering from sudden deafness or congenital deafness have been evaluated with regard to the number of nerve fibres and the morphological appearance. The meatal segment of cochlear nerves from 6 patients with sudden deafness shows a variable number of nerve fibres and different morphological changes. The duration of deafness does not correlate with the number of nerve fibres. In the case of congenital deafness for more than 17 years the cochlear nerve presented an apparently normal number of myelinated fibres. The presented study reveals that the retrograde degeneration of the human cochlear nerve is unpredictable.

Adolescent↗

PubMed2002

Temporal pattern of cochlear nerve degeneration following compression injury: a quantitative experimental observation.

OBJECT: It has been empirically recognized that the cochlear nerve is highly vulnerable to traumatic stress resulting from surgical procedures; therefore, careful manipulation of the cochlear nerve is mandatory in preventing trauma-induced hearing loss during cerebellopontine angle (CPA) surgery. There is, however, no precise knowledge about the temporal pattern of cochlear nerve degeneration following trauma. This study was performed to determine the temporal pattern of injury that occurs after cochlear nerve trauma, knowledge of which is indispensable not only to neurosurgeons but also to all those who manage lesions involving the cochlear nerve. METHODS: Right suboccipital craniectomies were performed in groups of rats with the aid of a surgical microscope, and the seventh and eighth cranial nerve trunks were identified at the internal auditory meatus. The cochlear nerve was quantifiably compressed while compound action potentials of the cochlear nerve were monitored and recorded. Following injury, one group of rats was killed for histological examination at the end of each week for 4 weeks. Data from this study disclosed that the degeneration of the compressed cochlear nerve progressed in a relatively rapid manner and was complete within 1 week after the insult. The main pathophysiological mechanisms responsible for cochlear neuronal death in this experimental setting appeared to be necrosis, and an apoptotic mechanism seemed to play a subsidiary role. CONCLUSIONS: Accurate knowledge about the temporal profile of trauma-induced cochlear nerve degeneration is closely linked with the problem of the therapeutic time window. The results of the present study indicated that any measures to ameliorate cochlear nerve degeneration following trauma should be started as early as possible (within 1 week) after an injury.

Animals↗

PubMedDate not supplied

Morphology of Human cochlear nerve after labyrinthectomy.

Five temporal bones and three surgical cochlear nerve specimens from patients who previously underwent labyrinthectomy were studied by light and electron microscopy. All cochleas had nearly total loss of sensory cells, extensive or total loss of both cochlear nerve fibers in the osseous spiral lamina, and spiral ganglion cells. In spite of this severe distal degeneration of the cochlear nerve, it processes within the internal auditory canal appeared normal in four of the five temporal bones, and the majority of the myelinated nerve fibers had survived in all three surgical specimens. Most of the central processes of the primary neurons of the cochlear nerve appear to have resisted retrograde degeneration when it was induced by a lesion primarily causing degeneration of the organ of Corti. This peculiar situation of a few nerve cell bodies and disproportionately large numbers of central axons is discussed.

Adult↗

PubMed2001

Macrophage invasion into injured cochlear nerve and its modification by methylprednisolone.

Post-traumatic invasion of macrophages into the cochlear nerve of the rat and measurement of how their invasion was modified by the administration of methylprednisolone were investigated for the first time by using a reproducible and quantifiable experimental model of cochlear nerve injury. Two weeks after precise cochlear nerve compression, a massive invasion of ED1 immunostained macrophages was observed at the compressed portion of the cochlear nerve, and this invasion of macrophages was markedly reduced in the rats to which methylprednisolone had been administered during the pre- and post-compression period. Concomitantly, the residual number of spiral ganglion cells was found to be greater in the compression+methylprednisolone group than in the control compression group. The tissue loss observed in the lesion epicenter was also significantly less in the compression+methylprednisolone group than in the control compression group. The results of our present study demonstrated the effectiveness of methylprednisolone treatment to ameliorate trauma induced cochlear nerve degeneration in the acute phase. However, these results may reflect the sum effects of methylprednisolone on macrophages, including both its beneficial effect by inhibiting the negative aspects of macrophages through attenuating macrophage recruitment to the lesion site, and at the same time an undesirable effect by sacrificing the positive aspects of macrophage function. Moreover, one reservation should be added that the protective effects of steroid to injured cochlear nerve may have operated via a pathway not related to macrophage function. Besides macrophages, various cells and factors participate in the process of CNS injury, and their effects may potentially work either positively or negatively with respect to CNS protection and regeneration at each particular time during the on-going process of CNS injury. Therefore, future investigation in CNS injury should be directed toward understanding such complex mechanisms involved in this process.

Action Potentials↗

PubMed2001

Methylprednisolone ameliorates cochlear nerve degeneration following mechanical injury.

We investigated whether methylprednisolone sodium succinate can ameliorate cochlear nerve degeneration following compression injury on the cerebellopontine angle portion of the cochlear nerve, using a quantitative animal experimental model that we have developed recently. In this model, cochlear nerve degeneration after compression could be quantitatively evaluated, while cochlear ischemia induced by the compression carefully maintained below the critical limit that causes irreversible damage to the cochlea. Eleven rats were treated with methylprednisolone during the pre- and post-compression period. Two weeks after compression, the numbers of SGC were compared between the rats that received the compression without and with methylprednisolone treatment. Methylprednisolone treatment improved the survival of SGC following cochlear nerve injury statistically highly significantly in the basal turn where the traumatic stress had been less than in the other cochlear turns in our experimental setting. Although it was not statistically significant, greater survival was also observed in the other cochlear turns. The results of this experimental study indicated that at least a portion of injured cochlear nerve had been potentially treatable, and that methylprednisolone might prevent such cochlear neurons from entering into the vicious process of irreversible damaging process.

Animals↗