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PubMed1999

Magnetic resonance cisternography used to determine precise topography of the facial nerve and three components of the eighth cranial nerve in the internal auditory canal and cerebellopontine cistern.

OBJECT: The detailed anatomy of intracranial structures has been studied mainly in cadavers, but the absence of cerebrospinal fluid and blood pressure in these models distorts normal spatial relationships. The authors investigated the rotation of the facial nerve (FN), superior vestibular nerve (SVN), inferior vestibular nerve (IVN), and cochlear nerve (CN) in the internal auditory canal (IAC) and cerebellopontine cistern in human volunteers and compared their results with those reported in cadaver studies. METHODS: The IACs and cerebellopontine cisterns of 30 normal adults (34 sides) were examined using magnetic resonance (MR) cisternography with a heavily T2-weighted two-dimensional fast spin-echo technique. The positions of the four components were unaffected by the presence of the meatal loop of the anterior inferior cerebellar artery in the IAC. The spatial relationship between the FN and SVN was quite constant, but the spatial relationship between the CN and SVN was quite variable: the former changed position, mainly in the IAC, on nine (26.5%) of 34 sides, and in the cerebellopontine cistern on the other sides (73.5%), conflicting with findings in cadaver studies. CONCLUSIONS: It is more accurate to describe the CN and IVN as coursing beneath the SVN in either the IAC or cerebellopontine cistern, rather than stating that the three components rotate, as reported in cadaver studies. The MR cisternography studies provided quite detailed information about the topography of the four components and the relationship between the blood vessels and cranial nerves in the IAC and the cerebellopontine cistern.

Adult↗

PubMed1991

The course of the internal auditory artery and its branches. Computer-aided three-dimensional reconstructions.

The course and branches of the internal auditory artery (IAA) were studied in 7 vertically-sectioned normal adult human temporal bones, and three-dimensional reconstructions of the anatomical structures were made with the aid of a computer system. Single IAAs existed in 3 or 7 temporal bones whereas double IAAs existed in 4. The IAA ran either between the facial nerve and the VIIth nerve, or on the inferior-posterior surface of the VIIIth nerve at the porus. Branching and anastomosis of the IAA were highly variable in the middle to proximal portion of the internal auditory canal (IAC). The anterior vestibular artery ran on the anterior surface of the superior vestibular nerve, and the vestibulocochlear artery ran on the inferior surface of the inferior vestibular nerve. The main cochlear artery ran at the center of the cochlear nerve near the fundus. The course of the vessels was less variable at the distal portion of the IAC than at the proximal portion.

Adult↗

PubMed1980

Cochlear mechanics: implications of electrophysiological and acoustical observations.

Implications of the spatial distribution of distortion products (2f1--f2) and (f2--f1) observed from populations of cochlear nerve fibers for cochlear mechanics are reviewed (the terms f1 and f2 represent the primary stimulus frequencies; f1 < f2). Characteristics of the distortion products (2f1--f2) and (f2--f1) in the ear-canal sound pressure of the cat and the chinchilla are investigated. Physiological origin of the acoustic distortion product (2f1--f2) is supported by demonstrations of the vulnerability of the distortion product to anoxia, to overstimulation and to cyanide perfusion of the cochlea. Observations are presented describing the dependence of levels of acoustic distortion products (2f1--f2) and (f2--f1): (1) on primary levels; (2) on f2 with iso-f1; and (3) on f1 and f2 with iso-(2f1--f2). Observations and interpretations are discussed in support of the conclusions: (1) that the distortion product (2f1--f2) in the ear-canal sound pressure observed in our studies is not generated in the experimental apparatus, in the eardrum, or in the middle ear but in the primary-frequency region of the cochlea; (2) that the distortion-product generation requires normal physiological processes in the cochlear sensory apparatus but not the neural activity; and (3) that the distortion-product is mechanically propagated from the generation region in the cochlea toward the distortion-frequency place and toward the stapes, through the middle ear, and into the ear canal involving gross motions of the cochlear partition and the middle-ear ossicles. It is now inevitable that we accept the notion that, in a normal ear, manifestations of significant nonlinear behavior are present in the mechanical response of the middle ear and the cochlea at most of the physiologically normal sound pressure levels.

Acoustic Stimulation↗

PubMed1988

Otosurgical aspects in diagnostics and therapy of acoustic neurinomas.

136 acoustic neurinomas were operated upon by otosurgical transtemporal or translabyrinthine interventions. The otosurgical approach was used when a suboccipital craniectomy with a certain retraction of the cerebellum seemed to be avoidable. The pure otosurgical tumour removal was restricted to a tumour extension up to 2.5 cm starting from the fundus of the internal auditory meatus. The transtemporal route was used when hearing was worth saving and the translabyrinthine when the pure tone auditogram showed an average loss of 50 dB or the speech audiogram a discrimination loss of 50% or more. In larger tumours the neurosurgeon removed the intracranial part of the acoustic neurinome preserving the facial nerve and, if possible, the cochlear nerve as well. If parts of the tumour had remained within the internal auditory meatus or if some uncertainty concerning complete tumour removal persisted, an otosurgical second intervention was considered indicated. In 41 patients the cochlear nerve could be preserved at operation. 12 of these patients showed a preservation of their hearing.

Audiometry, Pure-Tone↗

PubMed2004

Electrosurgery after cochlear implantation: eighth nerve electrophysiology.

HYPOTHESIS: Monopolar electrosurgery below the neck in cochlear implant recipients can be performed without damage to the internal cochlear stimulator, electrode array, and the cochlear nerve. STUDY DESIGN: Prospective pre- and postintervention electrically evoked compound action potential (ECAP) study of cochlear nerve function and behavioral sound perception assessment. METHODS: Neural response telemetry (NRT) was used to measure ECAPs before and after the use of monopolar electrosurgery during coronary artery bypass surgery to assess prosthetic device function and electrophysiologic function of the cochlear nerve. In addition, electrode voltage impedances and behavioral sound perception was measured at the same time intervals. RESULTS: ECAPs, behavioral sound perception, and electrode voltage impedances were within the normal range, within compliance, and similar preoperatively and on postoperative day 6. CONCLUSION: The studies reported herein were a series of measurements designed to test neural integrity and prosthetic device function before and after the use of monopolar electrosurgery. With appropriate precautions, use of monopolar electrosurgery below the neck in cochlear implant recipients can be performed safely.

Blood Loss, Surgical↗

PubMed1993

[Retrosigmoid-internal auditory canal approach operation].

We adopted a new operation which was developed and presented by Silverstein in 1987. It involves retrosigmoid craniotomy, removing the posterior wall of the IAC to the singular canal and exposing the cochlear nerve and every branch of the vestibular nerve. It can provide the accurate transection of the vestibular nerve. We suggest the operative indication should be expanded to cochlear neurectomy, for the operation can provide the accurate transection of the cochlear nerve too. A case of cochlear neurectomy, 2 cases of vestibular neurectomy were performed by this method. The operations were successful.

Adult↗

PubMed1989

Multichannel extracochlear implant.

The transcutaneous eight-channel extracochlear implant has undergone continuous revision to simplify the surgical technique, to minimize patient morbidity, and to improve performance. The extracochlear electrode array has been miniaturized so that it can be inserted through the facial recess without disturbing the external auditory canal, tympanic membrane, or malleus. The use of the remote antenna placed around the external auditory canal has greatly increased battery life and patient comfort. With its simplified incisions, the surgical procedure can be performed as out-patient surgery. Preoperative cochlear nerve testing and use of evoked response cochlear nerve testing allow preadjustment of the speech processor. Current features and performance of the implant are discussed.

Acoustic Stimulation↗

PubMed1984

Transganglionic transport of D-aspartate from cochlear nucleus to cochlea--a quantitative autoradiographic study.

This study concerns the connections of the inner and outer hair cells and the different types of ganglion cells of the mammalian cochlea with the central nervous system by making use of their putative neurotransmitters. D-[3H]Aspartate (D-ASP), a putative marker for glutamatergic neurons, was injected into the cochlear nucleus of cats and guinea pigs and the cochleas prepared for light microscopic autoradiography after varying survival times. A quantitative, statistical autoradiographic method is described. Grain counts per unit area were made for each of 14 tissue compartments in the cochlea and normalized to permit comparisons between cases. An operationally defined background labeling level was computed for each case and a statistical test for significance applied to the neuron-containing tissue compartments. With increasing survival times, significant labeling appeared successively in the cochlear nerve root, in each type of spiral ganglion cell, and in the neuron-containing tissue compartments of the organ of Corti. The findings are consistent with uptake of D-ASP and retrograde transport by cochlear nerve axons from the cochlear nucleus to the perikarya and peripheral processes of the spiral ganglion. We conclude that axons of all spiral ganglion cells project to the cochlear nucleus and that this nucleus is directly connected with both the inner and outer hair cells. Transganglionic transport of D-ASP from the cochlear nucleus is consistent with the hypothesis that the cochlear nerve axons use glutamate or aspartate as a neurotransmitter.

Animals↗

PubMed1998

[Prognostic factors for hearing preservation following observation-only versus stereotactic irradiation (STI) in patients with acoustic neuroma].

Prognostic factors for hearing preservation following observation-only versus STI were compared in patients with acoustic neuroma. There were 48 patients with acoustic neuroma treated by fractionated STI. Between 1991 and 1997, patients were given 36 Gy in 20 fractions over 5 weeks (36 Gy/20 Fr/5 wks) to 44 Gy/22 Fr/6 wks followed by a 4 Gy boost. A linear accelerator was used for irradiation. Twenty-three patients with acoustic neuroma who were followed without any treatment (observation-only group) were selected as matched controls. The largest hearing loss was observed at the frequency of 2 kHz in the observation-only group and at 1-2 kHz in the STI group. Hearing loss at 1 kHz was more frequent in the STI group (p < 0.01). There were no significant prognostic factors which predicted hearing preservation in the observation-only group. Stereotactic irradiation has been suggested to damage to cochlear nerve function in patients whose cochlear nerve had been impaired already. Tumor control rate of STI appeared to be as good as single fraction radiosurgery rates in the literature and better than in the observation-only group. Hearing preservation rate in the STI group was as good as in the observation-only group and appeared to be better than single fraction radiosurgery. In conclusion, because there were no factors predictive of hearing preservation in the observation-only group, it is difficult to select patients for observation only. Fractionated STI is potentially the treatment of choice, resulting in the same hearing preservation rate as achieved with observation only, although longer follow-up periods are needed.

Adult↗

PubMed1997

The number of primary auditory afferents in the rat.

Published estimates of the number of primary auditory afferents in the rat differ by as much as 30%. We undertook to determine if the widely varying estimates were related to methodological differences, especially the difference between counting cells in Rosenthal's canal and fibers in the cochlear nerve. Type I ganglion cells and myelinated cochlear nerve fibers in the same ears were counted in Long-Evans and Sprague-Dawley strains. Type II spiral ganglion cells were also counted. In each strain the numbers of myelinated fibers and type I ganglion cells were essentially the same. Means for the Long-Evans were 18,036 fibers and 17,749 cells. Means for Sprague-Dawleys were higher: 19,444 fibers and 19,229 cells. The mean number of type II ganglion cells was also greater in Sprague-Dawley than in Long-Evans rats: 1,388 and 1,170, respectively. Cell and fiber counts from the two ears of the same animal differed on average by only 1%. The number of auditory afferents did not change with age over the range (2-10 months) studied here. Several methodological differences have probably contributed to the varying estimates of type I primary auditory afferents, but the discrepancies are not inherent in counts of fibers and spiral ganglion cells.

Afferent Pathways↗

PubMed2000

[Determinants of the effectiveness of electric stimulation of the auditory nerve with cochlear implants: II. Configuration of the stimulating electrodes].

The influence of the electrode configuration on the efficacy of the electrical stimulation were investigated in the auditory nerve. For this purpose normal hearing cats were deafened by intrascalar application of neomycin and stimulated by a NUCLEUS-22 implant. Stimulation was performed in monopolar, bipolar and tripolar mode with all electrodes of the implant. The smallest thresholds were determined for monopolar stimulation, followed by tripolar and bipolar stimulation. The most focused stimulation was achieved by tripolar stimulation, followed by bipolar and monopolar stimulation. Tripolar stimulation is therefore suitable for beam forming in electrical stimulation of the auditory nerve.

Animals↗

PubMed1992

[Electrical tinnitus suppression--a comparative study of clinical trials and animal experiments].

Electrical tinnitus suppressor was newly developed and clinical study of electrical tinnitus suppression was discussed. Tinnitus was treated with this prototype suppressor in 38 ears out of 34 outpatients. Tinnitus was suppressed during electrical stimulation in all patients. After cessation of electrical stimulation, in 5 ears out of them tinnitus has disappeared at least for more than six months. In 12 ears it made tinnitus more than 10 dBHL softer for the following period, about six months. Hearing was unchanged in all patients. To know the mechanism how electrical stimulation of the cochlea suppressed tinnitus, animal experiments using a single fiber recording technique were made. A positive direct current on the cochlea suppressed the spontaneous activity of the cochlear nerve fiber, while a negative direct current increased the spontaneous activity. An alternative current on the cochlea increased the spontaneous activity of the cochlear nerve fiber. These electrical effects on the spontaneous activity were temporary. Therefore, after cessation of electrical stimulation on the cochlea, changed spontaneous activity restored to the level of prestimulation. Comparing temporary electrical effects on the spontaneous activity of cochlear nerve fiber with a longer suppression on tinnitus, tinnitus suppression following electrical stimulation of the cochlea was not thought to occur at the level of cochlea, but at auditory central nervous system.

Action Potentials↗

PubMed2004

[Refractory recovery function of electrical auditory on the survival auditory nerve in cochlear implant recipients].

OBJECTIVE: To evaluate the cochlear implant recipient's electrical auditory temporal properties in order to estimate the maximum stimulating rate which can be reached when they adopted some speech coding strategies based on time mechanism, such as continuous interleaved sampling (CIS). METHODS: Thirty-eight Nucleus CI24 cochlear implant recipients were divided into 4 groups by etiology and history. Their survival auditory nerve fibers' refractory recovery time function was measured via neural response telemetry (NRT). Electrical pulses with the amplitude of recipient's loudest acceptable presentation were stimulated in mono-polar mode, with the width of 25 microseconds and the frequency of 80 Hz. Least-squares regression procedures were used to fit individual recovery functions with the equation A = C + K e(-t/tau), in which tau is the time constant of recovery from refractory state. Statistic analysis showed the relationship between the time constants of individuals and etiology as well as electrode position in the cochlea. RESULTS: Congenital deaf patient's recovery time constants were shorter than that of postnatal deaf groups of ototoxicity (P = 0.0056) and large vestibular aqueduct syndrome (P = 0.0349). There was no significant difference between the recovery time constants of congenital deaf patients and those of group with long history of deafness. The ANOVA of the recovery time constants of 5th, 10th, 15th electrode showed no significant statistical difference (P > 0.05). CONCLUSION: The recovery time constants are related with etiology. In mono-polar mode, the time constants of congenital deafness or subjects with short duration of deafness are shorter than those of postnatal deafness or subjects with long duration of deafness. Time constants do not vary systematically with electrode location along the implanted array. The reciprocal of individual electrode seems to be used in determining the maximum of stimulating rate of CIS strategy and as criteria of choosing the usable channels from 22 electrode bands.

Acoustic Stimulation↗

PubMed1981

Morphology of axosomatic endings in an avian cochlear nucleus: nucleus magnocellularis of the chicken.

The axonal endings formed on the somata of neurons in the brainstem auditory nucleus magnocellularis (NM) were measured and classified in thin-sectioned material from adult chickens. Degeneration of primary endings after destruction of the basilar papilla and labeling of cochlear nerve fibers by injection of horseradish peroxidase (HRP) into the inner ear were used to determine which ending types arise from the cochlear ganglion. About 60% of the perikaryal surface is apposed by primary type terminals. These primary endbulbs are characterized by round clear synaptic vesicles distributed at an average density of 63 vesicles/micrometers 2 and a number of small, punctate, highly asymmetrical synaptic contacts. The primary type is the only class of endings which disappears after destruction of the basilar papilla and which is consistently labeled after HRP injections into the ear. These endings probably account for the "fast" EPSP seen in NM during stimulation of the cochlear nerve. NM neurons receive two types of nonprimary ending. About 13% of the perikaryal surface is apposed by a morphologically homogeneous class of small "symmetrical" endings; these are characterized by a flattened rhomboidal shape, numerous mitochondria, frequent coated vesicles, and small round or ovoid synaptic vesicles at an average density of 165 vesicles/micrometers 2. Most of the length of the apposition between ending and cell body is occupied by a synaptic complex with thin symmetrical presynaptic and postsynaptic densities. These endings were frequently found on short somatic processes. The second nonprimary axosomatic ending type in NM is most easily identified in experimental material; these endings occupy about 5% of the cell surface area and have a distinctly rounded profile in cross section. These endings typically exhibit clear round synaptic vesicles at a density of 111 vesicles/micrometers 2 arrayed before synaptic contacts which occupy a substantially larger fraction of the total apposition length than in the endbulbs. Many of these synaptic contacts show well-defined presynaptic grids and have postsynaptic densities intermediate in width between the endbulbs and the symmetrical endings. This second type of nonprimary ending may be responsible for the long-latency excitatory post-synaptic potentials seen in intracellular recordings from NM during electrical stimulation of the cochlear nerve. The morphology and distribution of the three ending types does not differ significantly along the posterior-to-anterior axis of NM.

Animals↗

PubMed2004

Organization of inhibitory feed-forward synapses from the dorsal to the ventral cochlear nucleus in the cat: a quantitative analysis of endings by vesicle morphology.

The main ascending, excitatory pathway from the cochlea undergoes synaptic interruption in the dorsal and ventral cochlear nuclei. The dorsal cochlear nucleus also forms a feed-forward circuit, which receives cochlear input and projects to the ventral cochlear nucleus by a tuberculo-ventral tract. This circuit may provide an inhibitory fringe (side bands) surrounding the center bands of the main ascending pathway. Biotinylated dextran injections into the dorsal cochlear nucleus anterogradely labeled the tuberculo-ventral tract and its endings in the anteroventral cochlear nucleus but also retrogradely filled cochlear nerve fibers and their terminals in the same regions. To distinguish tuberculo-ventral from cochlear nerve terminals, we used electron microscopy of the immunolabeled endings. Images were digitized and filter-enhanced, and the sizes and shapes of synaptic vesicles were used to construct quantitative profiles of the terminal types. The cochlear nerve endbulbs mapped to the same iso-frequency band of the injection site (main band). Flanking the main band were smaller labeled endings. About 45% of labeled terminals were pleomorphic and equally represented in the main band and side bands. Therefore, if there is an inhibitory fringe in the main projection pathway, it was not selective for tuberculo-ventral tract endings. Surprisingly, an excitatory category of round vesicles of intermediate size was labeled in the main band but not in the side bands. These intermediate endings may balance the feed-forward inhibition from the tuberculo-ventral tract. The quantitative method devised for classification of ending types by their vesicle profiles should be a generally useful tool for analysis.

Animals↗

PubMed1995

[Distribution and origin of corpola amylacea in the vestibulocochlear nerve].

The distribution of the corpora amylacea in the vestibulocochlear nerve is very limited. We studied the relation between the number of corpora amylacea in the cochlear nerve and the aging of cochlea and developed some hypotheses on the origin of corpora amylacea. This study involved 11 subjects, 14 samples. The results were as follows. There was no relationship between the number of corpora amylacea in the cochlear nerve and aging of the cochlea. Corpora amylacea probably have no relation to cochlear disorders. However, it was reported that corpora amylacea were produced more than 10 years after the organ's obstruction. There is a possibility that corpora amylacea increased 10 years after disorders developed in the cochlear nerve. There is a neurilemma-Schwann sheath junction (NSS junction) in the vestibulocochlear nerve. Corpora amylacea characteristically exist only in the central portion of the vestibulocochlear nerve on one side of the NSS junction. There are 3 possibilities regarding the origin of corpora amylacea which include consideration of the hypothesis that the NSS junction is the point where the vestibulocochlear nerve pierces the encephal dura mater. 1) Supposing that the origin of the corpora amylacea is the vestibulocochlear nerve itself, we would expect that the oligodendrocytes which are components of the vestibulocochlear nerve to be the origin of the corpora amylacea because they exist only in the central portion of the nerve, but not in peripheral portions of the nerve. 2) Supposing that the origin of the corpora amylacea is not the vestibulocochlear nerve itself, we would expect that the perineurium from the encephal dura mater to be the origin of corpora amylacea.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1991

Same location of the source of P1 of BAEPs and N1 of CAP in guinea pig.

The purpose of this study was to point out the location of N1 and N2 of the compound action potential (CAP) and the first waves of the brainstem auditory evoked potentials (BAEPs) by the mean of the section of the eighth nerve at the porus acousticus in guinea pigs. Our results agree with most of the studies in the literature. In the absence of lesion of the internal auditory artery, the section of the cochlear nerve induced the persistence, alone, of the P1 of BAEPs in which latency was similar to initial P1 before section, and the subsequent waves disappeared. Simultaneously, a monophasic negative potential (N1) of the auditory nerve remained without N2. When the section included the internal auditory artery all BAEPs and CAP components disappeared simultaneously and very suddenly just after the section. These results definitively excluded a proximal contribution of the cochlear nerve in the N1 of CAP and P1 of BAEPs. The N2 of CAP and P2 of BAEPs are not generated, even in part, in the intracochlear or intrapetrous portion of the cochlear nerve.

Action Potentials↗

PubMed2005

Advantages of magnetic resonance imaging over computed tomography in preoperative evaluation of pediatric cochlear implant candidates.

OBJECTIVES: To compare magnetic resonance imaging (MRI) to high-resolution computed tomography (HRCT) in the preoperative evaluation of pediatric cochlear implant candidates. METHODS: The charts of pediatric cochlear implant candidates evaluated between July 1, 2000 and November 30, 2003 with an MRI scan of the inner ear were included in the study. Fifty-six patients were included. Associated HRCT scans were examined. Abnormalities of the cochlea, cochlear nerve, endolymphatic sac, endolymphatic duct, vestibule, and modiolus were noted. A pediatric neuroradiologist gave an opinion as to whether patients with anomalies seen with MRI but without associated HRCT would have been identified by HRCT. RESULTS: Of the 112 temporal bones imaged with MRI, the following abnormalities were encountered: 32% (36/112) had abnormalities of the cochlear turns, 30% (34/112) had abnormal signal in the modiolus, 23% (26/112) had abnormal vestibulae, 16% (18/112) had abnormal endolymphatic ducts, 15% (17/112) had abnormal endolymphatic sacs, 12% (13/112) had abnormalities of the cochlear nerves, 29% (17/56) had abnormalities of the brain. HRCT cannot directly evaluate the cochlear nerve. Available HRCT findings were combined with radiologic opinion and compared with MRI findings. The percentages of abnormalities identifiable by HRCT when compared with those seen with MRI are cochlea 42% (15/36), modiolus 35% (12/34), vestibulae 88% (23/26), endolymphatic duct 100% (18/18), and endolymphatic sac 6% (1/17). CONCLUSION: MRI is more sensitive and specific in diagnosing soft tissue abnormalities in the inner ear than HRCT in cochlear implant candidates (Fig. 4). Moreover, the abnormalities detected with MRI are more likely to influence the implantation process (e.g., asymmetric nerve aplasia, cochlear obstruction). (Figure is included in full-text article).

Child↗