PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Cochlear Nerve”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources
PubMed2000

Cochlear schwannomas.

Schwannomas arising solely from the cochlear nerve and limited to the internal auditory canal are rare. Only three prior cases have been specifically described in the literature. We report a 38-year-old male with and asymmetric audiogram and poor discrimination. Magnetic resonance imaging revealed a 3-mm mass occupying the inferior portion of the internal auditory canal. Discrimination improved following a course of steroids, but thresholds did not. The patient underwent a translabyrinthine removal of the tumor, which was confirmed to involve only the cochlear nerve. It is important to obtain evidence regarding the possibility that a tumor confined to the internal auditory canal is a cochlear schwannoma. If so, surgery can be deferred until hearing is no longer functional or tumor growth mandates removal.

Case Reports↗
PubMed1993

Click-evoked otoacoustic emissions in a child with unilateral deafness.

In a 6-year-old boy with idiopathic unilateral deafness, click-evoked otoacoustic emissions were recorded in both ears with similar amplitudes and time courses. Following stimulation of the deaf ear, no component of auditory-evoked brainstem potentials was recorded. No space-occupying lesion was observed with high-resolution CT. At retest 1 year later these results were unchanged. In the deaf ear electrostimulation of the cochlear nerve was performed using an ear canal electrode. At a stimulus current of 20 microA the body consistently reported hearing sensation. Click-evoked otoacoustic emission indicated good outer hair cell function. Hearing sensation at low stimulus intensities with electrostimulation indicated fairly good functions of the cochlear nerve. Considering also the results of imaging and auditory-evoked potentials, findings suggested that the deafness was due to an inner hair cell disorder.

Acoustic Impedance Tests↗
PubMed2001

Functional anatomy of auditory brainstem nuclei: application to the anatomical basis of brainstem auditory evoked potentials.

Brainstem auditory evoked potentials (BAEP) are used routinely in clinical practice to evaluate the normality of the lower auditory system. The objective of this review is to describe the functional anatomy of the structures implicated in BAEP generation (cochlear nerve and the auditory brainstem nuclei). Indications and results of BAEP in clinical practice are presented and correlated with auditory structures, which generate each waveform of BAEP.

Auditory Pathways↗
PubMed1991

Delayed hearing loss after surgery for acoustic neurinomas: clinical and electrophysiological observations.

In a series of 26 patients with medium-sized and large acoustic neurinomas and documented hearing before surgery, 7 patients had preservation of hearing initially after the procedure but then developed delayed hearing loss. The most prominent intraoperative electrophysiological finding in these cases was a gradual deterioration of brain stem auditory evoked potentials (BAEP), especially of Wave V. Four additional patients with a similar gradual intraoperative loss of BAEP and severe postoperative hearing deterioration received vasoactive treatment after surgery (low-molecular weight dextran). In all 4 patients, including 1 patient with documented total deafness after surgery, hearing was preserved. Initial preservation of cochlear nerve function after the removal of an acoustic neurinoma does not guarantee postoperative hearing. Intraoperative BAEP help to identify patients at risk for delayed postoperative hearing loss. The pathophysiological mechanism can be attributed to disturbances of the microcirculation in endoneurial vasa nervorum caused by the mechanical manipulation of the cochlear nerve.

Adult↗
PubMed1985

Management of seventh and eighth nerve involvement by cerebellopontine angle tumors.

Microsurgical techniques have made a significant contribution in the advancement of surgery. Since then, the field of neurosurgery has made great and rapid strides. Neurosurgeons now venture through the deep and delicate regions of the brain where they dared not venture only a few years ago. In particular, the morbidity and mortality of surgery in the CPA has seen a progressive decrease. This presentation deals with 200 consecutive tumors in the CPA operated on using microsurgical techniques during the last 6 years. One hundred sixty-seven (83.5%) of them were acoustic neuromas (which included 12 patients with bilateral tumors). Of the remaining 33, there were 21 meningiomas, 10 epidermoids, and 2 angioblastomas. Preoperative investigation has been aimed at arriving at a diagnosis which is as exact as possible in order to plan the operative strategy. All patients, ranging in age from 16 to 84, have been operated upon in the lounging position (with the necessary precautions) through a unilateral suboccipital craniectomy. The basic surgical technique, irrespective of the tumor, is to decompress it from within in order to relieve its tension and pressure on surrounding nerves, vessels, and the brain stem. The structures which are only compressed are spontaneously relieved of compression. This helps define their full anatomic course. Having been identified, they are protected from damage. The most adherent points between tumor and nerves are recognized and handled last under direct vision when there is sufficient space to allow manipulation of the tumor. In the rare event of the facial nerve being interrupted, nerve graft procedures are attempted during the same operation. Our experience with the technique of intracranial-intratemporal facial nerve grafting has yielded excellent results. The cochlear nerve lacks a Schwann cell cover in the CPA and is more prone to being affected, either by tumor processes or surgical manipulation. Of our 167 acoustic nerve tumors, 60% were larger than 3 cm in diameter. The two important factors with regard to predicting the preservation of the seventh and eighth cranial nerves are tumor size (less than 3 cm) and preoperative hearing loss (less than 40 dB). The preservation of facial nerve function after tumor removal was achieved in 87.8% of patients. The facial nerve was preserved in all patients with other tumors. With regard to hearing ability the overall result of preservation of function was achieved in 27.6%. However, when a low hearing loss (less than 40 dB) and small tumor size (less than 3 cm) are taken into account, the preservation was as high as 58%.(ABSTRACT TRUNCATED AT 400 WORDS)

Aged↗
PubMed1985

A model for signal transmission in an ear having hair cells with free-standing stereocilia. I. Empirical basis for model structure.

No adequate theory for the signal-transmission properties of the peripheral auditory system exists for any vertebrate ear. Because the mammalian ear seems to pose conceptual and technical problems that complicate the development of an adequate theory, it is worthwhile to investigate simpler ears. The ear of the alligator lizard is simpler than mammalian ears in several respects: the motion of the basilar membrane is approximately independent of longitudinal position and is approximately linearly related to the sound pressure at the tympanic membrane; in a large region of the cochlea the hair cells have free-standing stereocilia that are not in contact with a tectorial membrane; the receptor potential of these hair cells is related to the sound pressure at the tympanic membrane in a relatively simple manner; the cochlear-nerve fiber responses from this region do not exhibit two-tone rate suppression. Also, the relative accessibility of this ear has enabled measurement of several response variables: tympanic-membrane volume velocity, extracolumella velocity, basilar-membrane velocity, hair-cell stereociliary displacement, hair-cell receptor potentials, and cochlear-nerve-fiber discharges. A model is developed to represent these results in terms of underlying anatomical structures and physiological mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Air Pressure↗
PubMed1987

Hearing preservation in acoustic neuroma surgery. Middle fossa versus suboccipital approach.

Over the past few years there have been reports discussing the preservation of hearing after the removal of acoustic neuromas through the middle cranial fossa or the suboccipital approaches. This is a complex issue with many facets and controversies. In an attempt to answer at least some of these controversies, this article reviews the experience of our group. Preservation of hearing was attempted in thirty-four cases out of 220 acoustic neuromas. In twenty cases the middle fossa approach was used: All tumors were less than 2 cm from the fundus, and in four patients the tumor was bilateral. In sixteen of the twenty (80%) the cochlear nerve was spared; in ten of twenty (50%) measurable hearing was retained, but in only four (20%) was the postoperative hearing serviceable according to the 50/50 rule. In fourteen cases the suboccipital approach was used: All but two of the tumors were smaller than 2 cm. In three patients the tumor was bilateral. The cochlear nerve was preserved in ten of the fourteen cases (71.4%). Measurable hearing was present in four of fourteen cases postoperatively (28.6%); none had serviceable hearing according to the 50/50 rule. Hearing was not preserved in any bilateral tumor case. The middle fossa and the suboccipital approaches are discussed as well as the relative merits of each procedure in preservation of hearing.

Adult↗
PubMed2006

Selective removal of lateral olivocochlear efferents increases vulnerability to acute acoustic injury.

Cochlear sensory cells and neurons receive efferent feedback from the olivocochlear (OC) system. The myelinated medial component of the OC system and its effects on outer hair cells (OHCs) have been implicated in protection from acoustic injury. The unmyelinated lateral (L)OC fibers target ipsilateral cochlear nerve dendrites and pharmacological studies suggest the LOC's dopaminergic component may protect these dendrites from excitotoxic effects of acoustic overexposure. Here, we explore LOC function in vivo by selective stereotaxic destruction of LOC cell bodies in mouse. Lesion success in removing the LOC, and sparing the medial (M)OC, was assessed by histological analysis of brain stem sections and cochlear whole mounts. Auditory brain stem responses (ABRs), a neural-based metric, and distortion product otoacoustic emissions (DPOAEs), an OHC-based metric, were measured in control and surgical mice. In cases where the LOC was at least partially destroyed, there were increases in suprathreshold neural responses that were frequency- and level-independent and not attributable to OHC-based effects. These interaural response asymmetries were not found in controls or in cases where the lesion missed the LOC. In LOC-lesion cases, after exposure to a traumatic stimulus, temporary threshold shifts were greater in the ipsilateral ear, but only when measured in the neural response; OHC-based measurements were always bilaterally symmetric, suggesting OHC vulnerability was unaffected. Interaural asymmetries in threshold shift were not found in either unlesioned controls or in cases that missed the LOC. These findings suggest that the LOC modulates cochlear nerve excitability and protects the cochlea from neural damage in acute acoustic injury.

Animals↗
PubMed2004

K(+) currents produce P(1) in the RW CAP: evidence from DC current bias, K(+) channel blockade and recordings from cochlea and brainstem.

Tone-burst-evoked compound action potentials (CAP) from the guinea pig round window (RW) are altered by DC current injection through the RW. The CAP waveform consists of a series of interleaved negative and positive peaks (N(1), P(1), N(2), P(2) etc.) of decreasing amplitude. During positive DC current injection (around +50 microA) the positive peaks are depressed substantially and there is an overall negative baseline shift of the waveform following the N(1). Negative current injection (around -50 microA) increased the positive peaks, in particular P(1), and produced an overall positive baseline shift following the N(1) peak. Results support our hypothesis that the first and dominant N(1) peak in the RW CAP is due to depolarising Na(+) currents into the primary afferent dendrites and axons within the cochlea, and that the P(1) potential is largely due to the exit of the hyperpolarising K(+) currents in the same cells. We have reached this conclusion on the basis of the sign and latency of the N(1) and P(1) components at the RW, beneath the myelin layers around the spiral ganglion cells, at the internal auditory meatus (IAM) within the brain case, and on the basis of the differential susceptibility of the various peaks to perfusion of lidocaine in the cochlear nucleus, sectioning of the cochlear nerve at the IAM, application of the K(+) channel blockers 4-amino-pyridine and tetraethylammonium within the cochlea, and DC current biasing at the RW.

4-Aminopyridine↗
PubMed1989

Cochlear ablation in deafness mutant mice: 2-deoxyglucose analysis suggests no spontaneous activity of cochlear origin.

Deafness mutant mice show no stimulus-related cochlear potentials as well as abnormal electrically-evoked responses recorded from the inferior colliculus. Abnormal spontaneous activity in the auditory periphery could result in abnormal development and/or maintenance of the central auditory pathways. We therefore assessed spontaneous activity of cochlear origin in the central nuclei of the mutants by ablating one cochlea and subsequently using the 2-deoxyglucose (2DG) technique to study metabolic activity. Any asymmetries in labeling in a given nucleus should be due to spontaneous activity in the cochlear nerve on the unoperated side. In control animals (+/dn mice undergoing unilateral cochlea ablation), statistically significant decreased 2DG labeling was observed in the ipsilateral PVCN and AVCN, and contralateral MNTB and IC; all receive primary excitatory input from the ablated ear. No significant differences in labeling between right and left sides were observed in any of the nuclei studied in the mutant animals. These findings suggest that there is no spontaneous activity of cochlear origin in these mutants, even though many cochlear nerve fibers and spiral ganglion cells survive.

Animals↗
PubMed1996

Surgical approach to the internal auditory meatus in acoustic neuroma surgery: significance of preoperative high-resolution computed tomography.

OBJECTIVE AND METHOD: To establish a surgical approach that provides better access to the internal auditory meatus (IAM) in acoustic tumor removal via a suboccipital transmeatal route, the anatomic location of the labyrinth with regard to the sigmoid-fundus line and the extent of bone removal from the IAM were evaluated by pre- and postoperative high-resolution computed tomography for 47 patients. RESULTS: The labyrinth was located lateral to the sigmoid-fundus line in 22 cases (lateral type, 46.8%), on the line in 9 (on-the-line type, 19.1%), and medial to the line in 16 (medial type, 34.0%). Postoperative high-resolution computed tomography showed that the mean length of the posterior wall from the fundus was shortened to 5.1 +/- 1.1 mm (n = 27) in the partially resected group and to 2.0 +/- 0.6 mm (n = 20) in the widely opened IAM group. The labyrinth was damaged in four cases from the widely opened IAM group; the preoperative status of the labyrinth was medial to the sigmoid-fundus line in three and on the line in one. The cochlear nerve was preserved in seven (31%) partially resected and in eight (50%) widely opened IAM cases. The overall success rate of hearing preservation was 4 of 22 (18.2%) partially resected and 5 of 16 (31.2%) widely opened cases. CONCLUSION: Preoperative evaluation of the anatomic relation between the IAM and the labyrinth by high-resolution computed tomography provides an efficient surgical approach to the IAM and contributes to anatomic and functional preservation of the cochlear nerve.

Female↗
PubMed1992

Late course of preserved hearing and tinnitus after acoustic neurilemoma surgery.

The late course of preserved hearing and tinnitus following retrosigmoid transmeatal surgery for acoustic neurilemoma is reported. Over a period of 5 years, useful hearing was preserved in 15 patients after preservation was attempted in 42 patients. In five patients the hearing was better than the preoperative level; in three it was worse. Three patients developed delayed worsening and fluctuations of hearing in the surgically treated ear during a median follow-up period of 2 1/2 years. While the exact reason for such worsening was not clear in two patients, in one patient it appeared that the muscle graft placed in the internal auditory canal after tumor resection resulted in fibrosis and compromise of the cochlear nerve. The causes of delayed worsening of hearing in the absence of tumor recurrence are analyzed, and possible treatment and methods of prevention of worsening are suggested. In six patients, tinnitus persisted after surgery in the ear with successful preservation of hearing, but hearing was not worsened and the tinnitus was not bothersome to the patient. In one patient with preoperative tinnitus, hearing was not preserved and tinnitus persisted sufficiently to necessitate reexploration and cochlear nerve section.

Adult↗
PubMed1990

Quantitative analysis of cochlear sensory cells and neuronal elements in man.

The myelinated radial fibres in the osseous spiral lamina and the myelinated fibres in the cochlear nerve in the internal auditory canal as well as the sensory cells were counted in cochleae from 15 dissected temporal bones from 8 patients. Light microscopy was carried out on semithin sections of epoxy resin embedded tissue. Audiometry had been performed within 6 months prior to death. Three patients had normal hearing for their age group, 2 had slight presbyacusis and the remaining 3 had sustained noise injury. All specimens clearly had fewer fibres in the spiral lamina than in the internal auditory canal. The cochleae from patients with normal hearing for their age group had a difference in the nerve fibre counts of up to 34%. A case of sensorineural presbyacusis showed 31%, and a case of neural presbyacusis, 47% difference. The greatest difference was found in a case of acoustic trauma, the range in this group being between 25% and 55%. The lower the number of fibres in the spiral lamina, the greater was the difference in all but two specimens. A slow retrograde degeneration, i.e. beginning in the peripheral process of the cochlear nerve, could be an explanation for these findings.

Aged↗
PubMed1987

Transtragal, transtympanic electrode placement for intraoperative electrocochleographic monitoring.

Transtragal, transtympanic electrode placement was performed for the purpose of intraoperative electrocochleographic (ECoG) monitoring during seven suboccipital acoustic neuroma resections. The promontory, the tragus, and two external sutures stabilized the electrode during surgery. The only noted otologic sequallae of electrode placement were small circular lesions at tympanic membrane puncture sites. Satisfactory ECoG recordings were obtained in five of seven cases. Peak-to-peak N1 amplitudes were (on average) 13.4-fold larger than the corresponding amplitudes of peak I of the surface-recorded brainstem auditory evoked potential (BAEP) recordings. During acoustic neuroma resection, ECoG and BAEP recordings changed relatively independently, which suggests multiple mechanisms and/or sites of injury to the cochlea or cochlear nerve. However, once they had become manifest, none of the observed changes exhibited a tendency to return to preoperative patterns. Hearing was preserved postoperatively in only two of seven patients, one of whom could not be monitored due to technical difficulty. Transtragal, transtympanic electrode placement provided a rapid, stable, and safe method of obtaining intraoperative ECoG recordings. Although combined intraoperative monitoring of ECoG and BAEP responses appeared to provide more precise documentation of injury to the cochlea and/or cochlear nerve, it was probably not influential in preservation of hearing in this series.

Adult↗
PubMed1997

The mechanism and site of action of lidocaine hydrochloride in guinea pig inner ear.

Lidocaine was applied to the round window (RW) in order to localize its site of action in the cochlea. Cochlear microphonic (CM), summating potential (SP), and compound action potential (CAP) input/output functions were measured to a 16 kHz tone burst to assess the functional changes of the cochlea. In separate experiments, the effect of lidocaine on the whole cell current of isolated outer hair cells (OHC) was studied. A dose of 2 microliters of 40 mM lidocaine in saline solution, when applied to the RW, caused a small change in all measured variables, indicating a passage of the drug through the RW membrane to sites of action. However, 160 mM of lidocaine further decreased CM, SP, and CAP by a total of 40% from the control. A partial recovery occurred for CM during the 30 min follow-up period. CAP and SP continued to decline. In isolated OHCs, lidocaine decreased the whole cell current in a dose-dependent fashion. The KD for lidocaine effect on OHCs was 7 mM. Our in vivo results indicate that lidocaine affects OHCs and reduces CM, causing a subsequent reduction in SP and CAP. The increased effect of lidocaine on CAP and SP, while CM is recovering, suggests an additional specific effect of lidocaine on the cochlear nerve and/or on inner hair cells. Considering that lidocaine alters OHC current (in isolated hair cells) and that lidocaine does not affect endocochlear potential [Laurikainen et al. Acta Otolaryngol (Stockh) 1991: 112: 800-9], the observed CM changes are most likely due to an in vivo effect on OHCs. Thus, the early effect of lidocaine on the cochlea appears to be due to a significant change in organ of Corti function, rather than to direct anesthesia of the cochlear nerve. Later, an independent effect of the drug may occur on neural tissues in the inner ear.

Animals↗
PubMed2000

Enhanced coding in a cochlear-implant model using additive noise: aperiodic stochastic resonance with tuning.

Analog electrical stimulation of the cochlear nerve (the nerve of hearing) by a cochlear implant is an effective method of providing functional hearing to profoundly deaf people. Recent physiological and computational experiments have shown that analog cochlear implants are unlikely to convey certain speech cues by the temporal pattern of evoked nerve discharges. However, these experiments have also shown that the optimal addition of noise to cochlear implant signals can enhance the temporal representation of speech cues [R. P. Morse and E. F. Evans, Nature Medicine 2, 928 (1996)]. We present a simple model to explain this enhancement of temporal representation. Our model derives from a rate equation for the mean threshold-crossing rate of an infinite set of parallel discriminators (level-crossing detectors); a system that well describes the time coding of information by a set of nerve fibers. Our results show that the optimal transfer of information occurs when the threshold level of each discriminator is equal to the root-mean-square noise level. The optimal transfer of information by a cochlear implant is therefore expected to occur when the internal root-mean-square noise level of each stimulated fiber is approximately equal to the nerve threshold. When interpreted within the framework of aperiodic stochastic resonance, our results indicate therefore that for an infinite array of discriminators, a tuning of the noise is still necessary for optimal performance. This is in contrast to previous results [Collins, Chow, and Imhoff, Nature 376, 236 (1995); Chialvo, Longtin, and Müller-Gerking, Phys. Rev. E 55, 1798 (1997)] on arrays of FitzHugh-Nagumo neurons.

Cochlear Implants↗
PubMedDate not supplied

Electrocochleographic study of sudden deafness.

By performing electrochleography (AP, SP and CM) on 34 patients with sudden deafness, it was thought that the pathophysiology of this disease could be deduced. The various waveform patterns of AP and SP responses obtained in cases of sudden deafness were classified into the following types: 1) AP high response; 2) decreased AP high response; 3) AP low response; 4) dominant -SP; 5) -SP or +SP; and 6) AP, SP no response. The cases showing the type of dominant -SP and AP high response had satisfactory prognoses. In these cases the sensory epithelium and the cochlear nerve seemed to indicate a reversible condition being affected by the temporary functional block. Furthermore, it seemed to indicate that the neural regions related to the source of AP(N1) response were impaired in cases in which CM were recorded at normal response threshold in spite of the absence of AP(N1) response. In the unsatisfactory prognosis cases with decreased AP high response, AP low response and AP, SP no response in which only the extremely low or depressed CM responses could be recorded, it seemed that the sensory epithelium and the cochlear nerve were affected permanently, although the degree of impairment varied.

Acoustic Stimulation↗