Morphology of the vestibular nerve. 3. Analysis of the calibers of the myelinated vestibular nerve fibers in man at various ages.
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Adult↗
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Vestibular nerve section.
INTRODUCTION: Vestibular nerve section is considered to be the most effective surgical procedure for control of intractable symptoms secondary to labyrinthine and eighth nerve function. This study was developed to retrospectively evaluate the efficacy of vestibular nerve section in patients treated for disabling labyrinthine dysfunction. METHODS: A retrospective review of hospital and office records was carried out on 39 patients who underwent vestibular nerve section. All patients received a comprehensive questionnaire to subjectively evaluate efficacy. RESULTS: Questionnaires were returned from 36 of 39 patients. Follow-up averaged 51 months. A decrease in vertiginous attacks was reported by 94% of patients. An improvement in activity tolerance was reported by 30% of patients. Preoperative tinnitus and ear fullness reportedly improved after surgery in 53% and 65% or patients respectively. Complications encountered included cerebrospinal fluid (CSF) leak (six patients), meningitis (two patients), and intracranial fluid collection (one patient). CONCLUSION: Vestibular nerve section is a relatively safe and effective method of treatment for intractable vertigo.
Activities of Daily Living↗
Monosynaptic vestibular nerve input to vestibular and adjacent reticular neurons projecting into the ascending medial longitudinal fasciculus.
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Action Potentials↗
Anatomic differences in the lateral vestibular nerve channels and their implications in vestibular neuritis.
HYPOTHESIS: Anatomic differences may render the superior division of the vestibular nerve more susceptible to injury during vestibular neuritis. BACKGROUND: Neural degeneration has been identified in temporal bone studies of vestibular neuritis. Previous anatomic and physiologic studies of vestibular neuritis have demonstrated that the superior division of the vestibular nerve is preferentially affected, with sparing of the inferior division. A preliminary temporal bone study has implicated neural entrapment as a possible cause for this preferential injury. METHODS: Two independent unbiased observers performed histologic analysis of 184 temporal bones from our temporal bone library. Measurements of the medial, midpoint, and lateral portions of the superior vestibular, inferior vestibular, and the singular nerves and their bony channels lateral to the internal auditory canal were made. These measurements included the length and width of each bony channel and an estimated percent of each channel occupied by bony spicules at each location. RESULTS: The lengths of the bony channels of the singular nerve (0.598 mm) and the inferior vestibular nerve (0.277 mm) were significantly shorter than the average length of the superior vestibular channel (1.944 mm; p < 0.0001). The total percent of the channel occupied by bone at the midpoint was significantly greater for the superior vestibular (28%) compared with either the singular (0%) or the inferior vestibular channel (18%) (p < 0.0001). CONCLUSION: The lateral bony channel of the superior vestibular nerve is seven times longer than the inferior vestibular and more than three times longer than the singular channel. There are a larger percentage of bony spicules occupying the superior vestibular compared with the inferior vestibular or singular channels. In addition, the superior nerve passes through a longer area of severe narrowing compared with the inferior or singular nerves. This anatomic arrangement of a longer bony channel with more interspersed bony spicules could make the superior vestibular nerve more susceptible to entrapment and ischemia.
Humans↗
Growth of postoperative remnants of unilateral vestibular nerve schwannoma: role of the vestibular ganglion.
Histopathological examination of seven temporal bones from patients who underwent a removal of vestibular nerve schwannomas by the translabyrithine or middle fossa approaches has demonstrated small tumor remnants that failed to grow as long as 25 years after surgery. In spite of the high incidence of residual tumors, the clinical recurrence rate of tumors operated at our institution by the translabyrinthine or middle fossa approaches is low (0.3%). Immunohistochemical labeling of dividing cells demonstrated that segments of tumor adjacent to the vestibular nerve and ganglion contained more dividing cells than were present in areas of the tumor at a distance from them.
Aged↗
Contributions of regularly and irregularly discharging vestibular-nerve inputs to the discharge of central vestibular neurons in the alert squirrel monkey.
The discharge of neurons in the vestibular nuclei was recorded in alert squirrel monkeys while they were being sinusoidally rotated at 2 Hz. Type I position-vestibular-pause (PVP I) and vestibular-only (V I) neurons, as well as a smaller number of other type I and type II eye-plus-vestibular neurons were studied. Many of the neurons were monosynaptically related to the ipsilateral vestibular nerve. Eye-position and vestibular components of the rotation response were separated by multiple regression. Anodal currents, simultaneously delivered to both ears, were used to eliminate the head-rotation signals of irregularly discharging (I) vestibular-nerve afferents, presumably without affecting the corresponding signals of regularly discharging (R) afferents. R and I inputs to individual central neurons were determined by comparing rotation responses with and without the anodal currents. The bilateral currents, while reducing the background discharge of all types of neurons, did not affect the mean vestibular gain or phase calculated from a population of PVP I neurons or from a mixed population consisting of all type I units. From this result, it is concluded that I inputs are canceled at the level of secondary neurons. The cancellation may explain why the ablating currents do not affect the gain and phase of the vestibulo-ocular reflex. While cancellation was nearly perfect on a population basis, it was less so in individual neurons. For some neurons, the ablating currents decreased vestibular gain, while for other neurons the vestibular gain was increased. The former neurons are interpreted as receiving a net excitatory (I-EXC) I input, the latter neurons, a net inhibitory (I-INH) input. When compared with the corresponding R inputs, the I inputs were usually small and phase advanced. Phase advances were larger for I-EXC than for I-INH inputs. The sign and magnitude of the I inputs were unrelated to other discharge properties of individual neurons, including discharge regularity and the phase of vestibular responses measured in the absence of the ablating currents. Unilateral currents were used to assess the efficacy of ipsilateral and contralateral pathways. Ipsilateral pathways were responsible for almost all of the effects seen with bilateral currents. The results suggest that the vestibular signals carried by central neurons, even by those neurons receiving a monosynaptic vestibular-nerve input, are modified by polysynaptic pathways.
Animals↗
Inputs from regularly and irregularly discharging vestibular nerve afferents to secondary neurons in the vestibular nuclei of the squirrel monkey. I. An electrophysiological analysis.
1. The electrical excitability of vestibular nerve afferents is related to their discharge regularity (23). Irregular (I) afferents are more excitable than regular (R) afferents. We explored the possibility that the differences in electrical excitability could be used to determine the profile of monosynaptic inputs from the ipsilateral vestibular nerve (Vi) to secondary neurons of the vestibular nuclei. The growth of monosynaptic Vi excitatory postsynaptic potentials (EPSPs) as shock strength is increased should reflect the kinds of afferent input that a secondary neuron receives. We were particularly interested in seeing if cells in the vestibular nuclei could be distinguished as R or I neurons depending on whether they received predominantly regular or irregular inputs. Barbiturate-anesthetized squirrel monkeys were used. 2. Recordings were made from vestibular nerve afferents. Shock strength was expressed as multiples of T, the value needed to recruit 10% of the afferents or, as determined empirically, to evoke a detectable field potential in the vestibular nuclei. Most I afferents (85/87 = 98%) were recruited below 4 X T, whereas most R afferents (197/212 = 93%) were first activated above 4 X T. The relation between latent period and electrical excitability was flat for units with thresholds in the range 1-4 X T. Latent periods increased for units with higher thresholds, especially those first activated above 8 x T. The threshold differences between I and R afferents are maximal if the shock falls at approximately half the mean interval after a naturally occurring action potential. The same results were obtained by having each unit fire to a maximal (16-32 X T) conditioning shock and then determining the threshold to a test shock presented 4 ms later. The latter stimulus configuration was used to study the Vi monosynaptic inputs to secondary neurons. The test shock was raised by successive doublings from 1 X T to the strength of the conditioning shock (16-32 X T). 3. Intracellular recordings were made from neurons located in the superior vestibular nucleus or the rostral parts of the medical or lateral vestibular nuclei. Amplitudes and latent periods of Vi EPSPs were measured from averages of several repetitions of each stimulus pair. Each EPSP was calculated by subtracting the extracellular from the intracellular averaged response. Of the 122 neurons sampled, 115 were judged to be monosynaptically related to the ipsilateral vestibular nerve because their Vi EPSPs had latent periods in the range of 0.7-1.4 ms.(ABSTRACT TRUNCATED AT 400 WORDS)
Action Potentials↗
Vestibular nerve activity in the alert monkey during vestibular and optokinetic nystagmus.
Activity of vestibular nerve fibers and eye movements were recorded in the alert monkey during natural stimulation. The animal was rotated about a vertical axis in the dark with velocity trapezoids (vestibular), or a striped cylinder was rotated around the stationary monkey ()optokinetic), or these stimuli were combined. After velocity steps in the dark, neuronal activity declined with a dominant time constant of 5-6 s. The time constant of nystagmus recorded simultaneously was always longer, on average 23 s. Vestibular nerve activity was not influenced by optokinetic patterns or additional visual stimuli during combined visual-vestibular stimulation. Thus, in contrast to vestibular nuclei neurons, vestibular nerve activity in the alert monkey is only determined by head acceleration and cannot be related to the nystagmus response or visual stimuli.
Animals↗
Eighth nerve in acoustic neuromas. Special reference to superior vestibular nerve function and histopathology.
Eighth nerve specimens were removed during acoustic neuroma surgery, and findings were related to cochlear and especially to superior vestibular nerve function as studied by conventional caloric testing in 21 cases. The origin of the tumor was in eight cases the inferior and in two cases the superior vestibular nerve, and in eight cases the vestibular nerve without more specific localization. In three advanced cases the exact site of origin could not be determined. Leaving age-related changes out of account, the utricle and horizontal canal ampulla appeared normal in all ears except one in which the ampulla was replaced by tumor tissue. In 11 ears the superior vestibular nerve was histologically intact and three of these ears also showed normal caloric responses. In seven ears there was a canal paresis, and in three no reaction was obtained. The ten ears with partial or total nerve invasion by tumor either showed a weak reaction or no response at all. It is likely that an early conduction block arises in both cochlear and vestibular nerves, and reduced reactions to appropriate stimuli do not warrant conclusions that the numbers of anatomically intact nerve fibers possibly are reduced.
Adult↗
An analysis of the retrolabyrinthine vs. the retrosigmoid vestibular nerve section.
Vestibular neurectomy is gaining widespread acceptance as a primary means of controlling medically refractory vertigo. However, debate continues over the adequacy of vestibular neurectomy within the cerebellopontine angle, long-term control, and the most appropriate surgical approach. To address these issues, we retrospectively reviewed 118 patients who underwent vestibular neurectomy between October 1984 and January 1988. Forty-two patients who underwent a retrolabyrinthine approach and 44 patients who underwent a retrosigmoid approach completed a written questionnaire and provided a recent audiogram. According to American Academy of Otolaryngology-Head and Neck Surgery guidelines, complete or substantial vertigo control was achieved and maintained in 95% of patients in both surgical groups. Hearing, tinnitus, and fullness results over the long term are variable. The advantages and disadvantages of the various vestibular neurectomy approaches will be detailed. On review of our results and surgical experience, we now prefer the retrosigmoid approach.
Adult↗
Inputs from regularly and irregularly discharging vestibular nerve afferents to secondary neurons in the vestibular nuclei of the squirrel monkey. II. Correlation with output pathways of secondary neurons.
1. Intracellular recordings were made from secondary neurons in the vestibular nuclei of barbiturate-anesthetized squirrel monkeys. Monosynaptic excitatory postsynaptic potentials (EPSPs) evoked by stimulation of the ipsilateral vestibular nerve (Vi) were measured. An electrophysiological paradigm, described in the preceding paper (26), was used to determine the proportion of irregularly (I) and regularly (R) discharging Vi afferents making direct connections with individual secondary neurons. The results were expressed as a % I index, an estimate for each neuron of the percentage of the total Vi monosynaptic input that was derived from I afferents. The secondary neurons were also classified as I, R, or M cells, depending on whether they received their direct Vi inputs predominantly from I or R afferents or else from a mixture (M) of both kinds of Vi fibers. The neurons were located in the superior vestibular nucleus (SVN) or in the rostral parts of the medical or lateral (LVN) vestibular nuclei. 2. Antidromic activation or reconstruction of axonal trajectories after intrasomatic injection of horseradish peroxidase (HRP) was used to identify three classes of secondary neurons in terms of their output pathways: 1) cerebellar-projecting (Fl) cells innervating the flocculus (n = 26); 2) rostrally projecting (Oc) cells whose axons ascended toward the oculomotor (IIIrd) nucleus (n = 27); and 3) caudally projecting (Sp) cells with axons descending toward the spinal cord (n = 13). Two additional neurons, out of 21 tested, could be antidromically activated both from the level of the IIIrd nucleus and from the spinal cord. 3. The Vi inputs to the various classes of relay neurons differed. As a class, Oc neurons received the most regular inputs. Sp neurons had more irregular inputs. Fl neurons were heterogeneous with similar numbers of R, M, and I neurons. The mean values (+/- SD) of the % I index for the Oc, Fl, and Sp neurons were 34.7 +/- 24.7, 51.9 +/- 30.4, and 61.8 +/- 18.0%, respectively. Only the Oc neurons had a % I index that was similar to the proportion of I afferents (34%) in the vestibular nerve (cf. Ref. 26). 4. The commissural inputs from the contralateral vestibular nerve (Vc) also differed for the three projection classes. Commissural inhibition was most common in Fl cells: 22/25 (88%) of the neurons had Vc inhibitory postsynaptic potentials (IPSPs) and 1/25 (4%) had a Vc EPSP. In contrast, Vc inputs were only observed in approximately half the Oc and Sp neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Action Potentials↗
Vestibular nerve compression in eighth-nerve tumors.
The superior vestibular nerve was studied histologically in 25 patients who underwent removal of inferior vestibular nerve schwannoma. In most cases, the nerve fibers were structurally normal but the endoneurial space showed various degrees of capillary stasis and/or extravasation of red blood cells. Increased fibrosis of the endoneurial space was seen in about two-thirds of the cases; it was mild in all except two cases. The endoneurial space appeared edematic in about one-third of the cases. Wallerian degeneration of individual fibers was occasionally observed in most cases and was severe in the two cases with moderate or severe endoneurial fibrosis. In about one-third of the cases there were large numbers of myelinated nerve fibers with thinned myelin sheaths. The observed structural changes are compatible with those seen in human and experimentally induced chronic compressive or entrapment neuropathies. Thus, early symptoms of eighth-nerve tumors might develop due to direct compression of the eighth-nerve trunk within the internal auditory canal.
Cranial Nerve Neoplasms↗
Effect of vestibular nerve section on cytochrome oxidase activity in the vestibular ganglion cells of the squirrel monkey.
Cytochrome oxidase (CO) activity of the vestibular ganglion cells of the squirrel monkey was demonstrated histochemically under normal and experimental conditions. Under general anesthesia, right vestibular nerve section was performed on adult squirrel monkeys between the vestibular ganglion and brain stem. The left side was left intact and was used as a within-animal normal control. One squirrel monkey that did not undergo vestibular nerve section was also included in the normal group. Following a survival period of seven months, neurons in the vestibular ganglion of both sides were examined. In the normal control sides, a significant negative correlation between the size of the neuron and its optical density for CO stain was observed. Many neurons in the vestibular ganglion survived after vestibular nerve section, but their cell sizes and optical densities of CO stain decreased compared with those of the control side.
Animals↗
Influence of lateral rectus muscle contractions on the abducens nerve discharge evoked by vestibular nerve stimulation.
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Abducens Nerve↗
Hearing outcome after concurrent endolymphatic shunt and vestibular nerve section.
OBJECTIVE: To determine if endolymphatic shunt surgery concurrent with vestibular nerve section improves hearing outcome compared with vestibular nerve section alone. STUDY DESIGN: Retrospective observational study with cross-sectional survey. SETTING: Tertiary otologic private practice. PATIENTS: Thirty-five patients who underwent vestibular nerve section and endolymphatic shunt surgery and 17 patients who had vestibular nerve section alone between 1985 and 2000. METHODS: Chart review and correspondence for audiogram results and survey. MAIN OUTCOME MEASURES: Hearing at last follow-up. Hearing Handicap Inventory, Dizziness Handicap Inventory, Tinnitus Handicap Inventory, and SF-36. RESULTS: Eight patients in the vestibular nerve section and 15 in the vestibular nerve section and endolymphatic shunt surgery group had an audiogram at more than 16 months after surgery available for review. In the vestibular nerve section group, three patients had same hearing whereas five were worse. In the vestibular nerve section and endolymphatic shunt surgery group, 2 patients showed improvement, 2 were the same, and 11 were worse. There was no significant difference in the change from preoperative pure tone average or Word Discrimination Score to postoperative levels between the surgical groups. Eighteen patients had serviceable hearing preoperatively. Five of 8 in the vestibular nerve section and 4 of 10 in the vestibular nerve section and endolymphatic shunt surgery groups maintained serviceable hearing postoperatively. Of the 52 patients, 33 responded to the survey (63%). There were no significant differences between the groups for Dizziness Handicap Inventory, Hearing Handicap Inventory, Tinnitus Handicap Inventory, or SF-36, suggesting that patient-oriented outcomes are the same in both groups. CONCLUSIONS: Concurrent endolymphatic shunt surgery and vestibular nerve section does not improve hearing or tinnitus outcome over vestibular nerve section alone.
Audiometry, Pure-Tone↗
The morphology of the vestibular nerve in a patient with normal vestibular function and in patients with Ménière's disease.
The morphology of the vestibular nerve was studied in three fresh nerve specimens obtained by surgery from two patients with Ménière's disease and one patient with tinnitus after an attack of sudden deafness. The number of nerve fibres appeared light microscopically normal. The vestibular ganglion cells of the Ménière-specimens showed, as a characteristic finding advanced vesiculation of the cytoplasm. This change was confirmed by electron microscopy and the vacuoles appeared to consist of widened endoplasmic reticulum cisternae. Numerous primary lysosomes and lipofuscin granules were observed in all vestibular ganglion cells but their number appeared increased in the specimens from Ménière-patients. Some of the vestibular ganglion cells of these patients showed a filamentous appearance and the number of glycogen granules seemed reduced in all of them. All vestibular ganglion cells observed were unmyelinated. The degenerative changes observed might explain the typical elevation of the threshold for vestibular stimulation in Ménière's disease.
Adult↗
Morphometric nerve fiber analysis and aging process of the human vestibular nerve.
Myelinated and unmyelinated nerve fibers of the human vestibular nerve were analyzed with the use of a new staining method that makes it possible to discriminate various structures of the nervous tissue. An image-analyzing digitizer, a microscope with a drawing tube and a personal computer for storing data and performing statistical analyses were employed in this study. We measured the axonal numbers and transverse areas of myelinated vestibular nerve fibers in 20 cadavers, and of unmyelinated fibers in 14 cadavers. The average number of myelinated axons and unmyelinated axons were 20,318 and 2,782, and the average transverse area of their axons were 3.46 and 0.49 micron 2, respectively. The transverse areas of myelinated axons decreased with age, although the numbers of their axons did not change. However, in the case of unmyelinated axons, both the transverse areas and the numbers did not change.
Aged↗
[Modifications of the activity of the vestibular nerve after stimulation of the vestibular system].
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Humans↗