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PubMed1992

Clinical and vestibulometric status following labyrinthectomy or vestibular nerve section for Menière's disease.

A clinical and vestibulometric comparison of 10 patients following labyrinthectomy, 5 following vestibular nerve section, and 10 control subjects was undertaken in order to evaluate the long-term effectiveness of these procedures. Testing was performed a mean of 8.5 years after surgery. Vestibulometry assessed time constants, gain, and phase advance of the vestibulo-ocular reflex (VOR) in both horizontal and vertical planes of head movement. Loss of the anticipated increase in phase advance in the vertical VOR of the labyrinthectomy group, significantly different from the vestibular nerve section group (P less than 0.05 and P less than 0.01 for each direction of rotation), suggests that posterior and superior semicircular canal function remains intact following per-meatal labyrinthectomy. Although stabilometry suggested that balance in the labyrinthectomy group was poorer than in the two other groups (P less than 0.025 without optic fixation), clinical assessment demonstrated excellent functional results. Per-meatal labyrinthectomy remains a safe and effective procedure for the relief of vestibular symptoms, although vestibular nerve section may provide more complete removal of contributory end-organ function.

Aged↗
PubMed1997

Effect of streptomycin intoxication on vestibular nerve regeneration and posture recovery.

The action of streptomycin sulfate (SM) on the regenerative process of the vestibular nerve and posture recovery was studied, using bull frogs. The vestibular nerve was sectioned in various conditions with intact endorgan or with SM intoxication. When the nerve was sectioned with the hair cells left intact, the nerve regenerated well and body balance recovered to normal. However, when neural regeneration was blocked, recovery was incomplete. SM intoxication resulted in various degrees of hair cell damage. Degree of posture recovery correlated well with the number of hair cells. When the nerve was sectioned after damaging the hair cell, the nerve failed to regenerate and posture recovery was incomplete. These results suggest that the degree of posture recovery depends on hair cell function and neural regeneration. Furthermore, neural regeneration is strongly influenced by hair cell function.

Animals↗
PubMedDate not supplied

Behavior of the vestibular nerve following labyrinthectomy.

Transtympanic labyrinthectomy was performed on 24 cats, and after survival times of one month to three years, the temporal bones were prepared for light microscopic study. The operated ears showed mean neuronal losses of 12% in six months, 24% in 1 year, 35% in 2 years, and 53% in 3 years. These was no evidence of regeneration of vestibular nerve fibers nor of formation of traumatic neuromata. The temporal bones of two human subjects who had undergone transtympanic labyrinthectomy are also presented; one shows atrophy of the vestibular nerves while the other exhibits proliferation of nerve fibers not resembling a neuroma. It is concluded that the afferent vestibular nerves undergo slow but progressive atrophy following labyrinthectomy and that they have no potential for the creation of amputation neuromata. The evidence suggests that excision of the vestibular nerves may have no therapeutic advantage over labyrinthectomy in the treatment of intractable vertigo.

Animals↗
PubMed1997

Differential central projections of physiologically characterized horizontal semicircular canal vestibular nerve afferents in the toadfish, Opsanus tau.

Anatomical and neurophysiological studies were undertaken to examine the central projection pattern of physiologically characterized horizontal semicircular canal vestibular nerve afferents in the toadfish, Opsanus tau. The variations in individual response characteristics of vestibular nerve afferents to rotational stimulus provided a means of typing the afferents into descriptive classes; the afferents fell into a broad continuum across the spectrum from low-gain, velocity-sensitive to high-gain, acceleration-sensitive responses (Boyle and Highstein [1990b] J. Neurosci. 10:1557-1569; Boyle and Highstein [1990a] J. Neurosci. 10:1570-1582). In the present study, each afferent was typed as a low-gain, high-gain, or acceleration fiber during rotational or mechanical stimulation (Rabbitt et al. [1995] J. Neurophysiol. 73:2237-2260) and was then intracellularly injected with biocytin. The axons were reconstructed, and the morphology, synaptic boutons, and projection pattern of each axon were determined. The results indicated that the three descriptive classes of vestibular nerve afferents have unique as well as overlapping central projection patterns and destinations in the vestibular nuclei, with intranuclear parcellation in the anterior octavus, magnocellularis, tangentialis, posterior octavus, and descending octavus nuclei. In general, increased sensitivity and faster response dynamics were correlated with both a more extensive central projection and a progressive increase in morphological complexity. Low-gain, velocity-sensitive fibers were the simplest morphologically, with the fewest number of branches (n = 17) and shortest length (4,282 microm), and projections were confined to the middle portions of the vestibular nuclei. High-gain, velocity-sensitive fibers were morphologically more diverse than low-gain fibers, with a greater number of branches (n = 26), longer length (6,059 microm), 29% greater volume, and a more widespread projection pattern with projections to both the anterior and the middle portions of the vestibular nuclei. Acceleration fibers were morphologically distinct from low- and high-gain fibers, with more elaborate branching (n = 41), greatest overall length (17,370 microm) and volume (16% greater than high gains), and displayed the most extensive central projection pattern, innervating all vestibular nuclei except tangentialis. Thus, there are anatomically demonstrable differential central projections of canal afferents with different response dynamics within the vestibular complex of the fish.

Animals↗
PubMed1975

Occult schwannomas of the vestibular nerve.

Five small occult schwannomas of the vestibular nerve were discovered on routine examination of 893 serially sectioned temporal bones of 517 individuals. Three arose from the superior division, one from the inferior division, and the other had a multicentric origin from both divisions of the nerve. Location and size of these tumors indicate that clinical diagnosis would have been difficult or impossible by any method of study. The finding of vestibular schwannomas in 0.9% of individuals in this series, indicates the high incidence of this tumor in the general population. The much lower incidence of diagnosed symptomatic tumors in the general population can only be explained by the conclusion that this neoplasm exhibits considerable variation in growth characteristics. Usually the tumor enlarges so slowly as to be of no health importance, but occasionally it grows more rapidly to become symptomatic and require surgical removal.

Aged↗
PubMed1992

Retrolabyrinthine vestibular nerve section: evaluation of technical modification in 143 cases.

Selective vestibular nerve section is effective in relieving intractable vertigo while preserving hearing. Histologic study demonstrated overlap of the cochlear and vestibular fibers at the cochleovestibular cleavage plane within the posterior fossa. In the hopes of improving surgical results by sectioning these overlapping vestibular fibers, the technique of sectioning the vestibular division of the eighth nerve was modified to include a small portion of the cochlear division. We have evaluated 143 cases of retrolabyrinthine vestibular nerve section in which this technical modification was employed. A patient questionnaire was used to examine control of vertigo as well as changes in tinnitus, unsteadiness, and disability. Hearing preservation and incidence of complications were also reviewed. Resolution or improvement of vertigo occurred in 93 percent of Menièré's cases and 74 percent of non-Menièré's cases as compared to 97 percent and 68 percent, respectively, in the pre-1986 series.

Adult↗
PubMed1989

Persisting nystagmus following vestibular nerve section for Menière's disease.

Unilateral vestibular nerve section (VNS) creates a state of acute dysequilibrium which resolves by a process of central compensation. This disturbance resolves quickly and central compensation is complete generally within a month with resolution of symptoms and signs. The course of central compensation following VNS will be similar to that seen after labyrinthectomy because the detachment of hemi-labyrinthine input that is achieved by both will be identical. Six patients are presented who have undergone VNS at least 2.7 years ago (Average 3.5 years); all of them have persisting spontaneous peripheral type horizontal jerk nystagmus, present with optic fixation in five. This is obvious clinically and was confirmed in each case by agreement of three independent observers and has been recorded by electronystagmography (ENG). They are free from marked vestibular symptoms. The explanations of mechanisms involved in central compensation are discussed with respect to this previously unrecorded clinical observation.

Adult↗
PubMedDate not supplied

[Vestibular nerves and nuclei throughout history].

Throughout the evolution of the concepts concerning the peripheral nerves, different ideas have dominated at different moments in history. The studies and demonstrations conducted in an attempt to further our knowledge of our own constitution and working at the same time enabled us to gain a better understanding of the make-up and specific functioning of the vestibular nerves, together with their central connecting elements in the brainstem: the vestibular nuclei. It may be that the first references to vestibular nerves are now lost in time, yet the Ancient Greeks already attempted to understand their functional nature by carrying out studies essentially focused on neuroanatomical aspects, but heavily influenced by philosophical concepts. It was not until the 18th century that researchers came to understand that there were differences between the vestibular nerve and the cochlear nerve --until then they were believed to be one single nerve. Another century went by before attempts were made to clarify the role it plays in balance and not in hearing. The differences between the distinct vestibular nuclei situated between the medulla oblongata and the pons were established in the 19th and 20th centuries when a number of authors, backed by previous microscopic studies, contributed to clarifying the fuzzy limits of cells separating the four classic nuclear groups and four others taken as being accessory.

History, Ancient↗
PubMed2004

Swimming behaviour and calcium incorporation into inner ear otoliths of fish after vestibular nerve transection.

Previous investigations on neonate swordtail fish (Xiphophorus helleri) revealed that otolithic calcium incorporation (visualized using the calcium tracer alizarin complexone) and thus otolith growth had ceased after nerve transection, supporting a hypothesis according to which the gravity-dependent otolith growth is regulated neuronally. Subsequent investigations on larval cichlid fish (Oreochromis mossambicus) yielded contrasting results, repeatedly depending on the particular batch of cichlids investigated. Like most neonate swordtails, Type I cichlids revealed a stop of calcium incorporation after unilateral vestibular nerve transection. Their behaviour after transection was normal, and the otolithic calcium incorporation in controls of the same batch was symmetric. In Type II cichlids, however, vestibular nerve transection had no effect on otolithic calcium incorporation. They behaved kinetotically after transection (this kind of kinetosis was qualitatively similar to the swimming behaviour exhibited by larval cichlids during microgravity in the course of parabolic aircraft flights). The otolithic calcium incorporation in control animals was asymmetric. These results show that the effects of vestibular nerve transection as well as the efficacy of the mechanism, which regulates otolith growth/otolithic calcium incorporation, are--depending on the particular batch of animals--genetically predispositioned. In conclusion, the regulation of otolithic calcium incorporation is guided neuronally, in part via the vestibular nerve and, in part, via a further pathway, which remains to be addressed in the course of future investigations.

Animals↗
PubMed1989

Long-term hearing results following middle fossa vestibular nerve section.

Hearing stabilization following middle fossa vestibular nerve section (MFVNS) has been observed to occur in a large percentage of patients (71% to 86%) after short-term followup. This study looks at the long-term audiological followup (5 to 15 years) of 46 patients who underwent a MFVNS for intractable Meniere's disease. Although the percentage of patients with stabilized hearing was relatively high within the first 2 years postoperatively (61%), it dropped to 41% after a longer followup of 5 to 15 years. When this patient population is divided into two groups based on their preoperative PTA, those patients in whom hearing had bottomed out to greater than or equal to 50 dB PTA preoperatively lost only 5 dB PTA over the course of the follow-up period. The patients with better preoperative hearing (less than 50 dB PTA) lost 30 dB PTA over the same follow-up period. As this pattern is similar to what has been observed in nonsurgically treated Meniere's patients, we conclude that the MFVNS has no beneficial effect on the hearing loss associated with Meniere's disease.

Adult↗
PubMed1998

Long-term deficits in otolith, canal and optokinetic ocular reflexes of pigmented rats after unilateral vestibular nerve section.

Static and dynamic otolith, horizontal vestibular and optokinetic ocular reflexes were investigated in pigmented rats 1-6 and more months after unilateral vestibular nerve (UVN) section. Evoked responses were compared with published data from control rats studied under identical conditions. Static lateral tilt of UVN rats in the light evoked a vertical deviation in static eye position that was as large as in controls. In darkness, the evoked responses in UVN rats 6 months after the lesion were consistently smaller than in controls. Linear horizontal acceleration in darkness evoked vertical and torsional response components in UVN rats that were parallel-shifted towards lower gains and larger phase lags. Off-vertical axis rotation on a platform provoked responses that differed markedly from those recorded in intact rats with respect to the bias velocity component. These results suggest a permanent deficiency in the static and dynamic otolith-ocular reflex performance of UVN rats. Ocular responses to horizontal table velocity steps in darkness exhibited a direction-specific asymmetry in UVN rats. Step responses evoked by acceleration towards the intact side were larger in gain and longer in duration than responses evoked by acceleration towards the operated side. When compared with control data, responses to either side were reduced in UVN rats and the velocity store mechanism was barely activated by velocity steps towards the operated side. Responses evoked by horizontal optokinetic stimulation with constant pattern velocities were below control values in either direction. Slow-phase eye velocity saturated at much lower values than in intact rats, particularly during pattern motion towards the intact side. The duration of the optokinetic afternystagmus was asymmetrically reduced with respect to control data. Practically identical reductions in duration were found for vestibulo-ocular responses in the opposite directions. Behaving animals exhibited no obvious impairment in their spontaneous locomotory or exploratory activities. However, each UVN rat was impaired, even 2 years after the lesion, in its postural reaction to being lifted by the tail in the air. This observation suggests the presence of a permanent deficit in static and dynamic otolith-spinal reflexes that may be substituted on the ground by proprioceptive inputs.

Animals↗
PubMedDate not supplied

Second-order neural responses after contralateral vestibular nerve sectioning.

The characteristics of the response to an 8 degrees/sec2 acceleration of 41 neurons in the medial vestibular nucleus of the cat following vestibular nerve sectioning were compared with those of 73 control neurons at the same site. In 14 of the vestibular nerve-sectioned animals the same neuron was recorded before and after sectioning. No difference was found between the resting discharge rates, maximal response rates, and rates of adaptation of the two groups. Following contralateral vestibular nerve sectioning Type II neurons were still plentiful, suggesting many receive ipsilateral labyrinthine innervation.

Action Potentials↗
PubMed1980

Vestibular nerve in Meniere's disease.

Biopsy specimens of vestibular nerves of 40 patients with severe Meniere's disease were studied by microscopy. In 17 patients, a translabyrinthine eighth nerve transection was done; in 23 patients, a middle fossa vestibular neurectomy was done. Many of the nerve fibers had thickened and deformed myelin coats; some were thinly myelinated fibers and some showed degraded myelin. No macrophages were present. Occasional vestibular ganglion cells had thin myelin coats. In six patients, there were lighter areas between the fibers. In these there were roughly parallel astrocyte processes, with numerous cytoplasmic filaments. The light areas were surrounded by a basement membrane. Four of these patients showed continuation of vertiginous symptoms after operation and were not helped by surgery. These patients may suffer from a neuropathy that is different from the more common causes of Meniere's disease.

Adult↗
PubMed1986

Operations on the saccus endolymphaticus and vestibular nerve: have they fulfilled their promise?

The rationale for operations on the saccus and vestibular nerve in patients incapacitated by Meniere's disease as a replacement for total labyrinthectomy, has been the expectancy that less radical procedures will protect these patients from total auditory incapacity. Aware of postoperative hearing losses in some patients after 3 years, we have studied the results in 21 Shambaugh saccus decompression (SD) and 29 middle fossa vestibular nerve section (VNS) operations, in order to assess the claims made for these procedures. We found that while control of vertigo was similar to that reported elsewhere, worse hearing (AAOO criteria) developed in many cases. With SD this increased from 14% at 1 year to 58% at 10 years, and with VNS it increased from 17% at 1 year to 48% at 10 years, when the worse preoperative audiogram was used. Only 17% of SD and 11% VNS ears with serviceable best preoperative hearing had retained this at 10 years. Nineteen percent developed audiometric evidence of contralateral disease during the first 10 postoperative years. It is concluded that although, regrettably, neither of these surgical therapies appears to have the capability of preventing the progress of hearing loss, the reality of bilateral disease justifies the continued use of SD or VNS by adequately trained surgeons.

Ear, Inner↗
PubMed1979

The cerebellar projection of the vestibular nerve in the cat.

The projection of the vestibular nerve to the cerebellum of the cat was examined with silver degeneration methods after complete lesions of the vestibular ganglion. The majority of the primary vestibular afferents were traced to the cortex of the ipsilateral nodulus and uvula, relatively fewer entering the ipsilateral flocculus. Fibers were not traced to the paraflocculus, lingula or lateral cerebellar nucleus. A sparse projection to the ipsilateral fastigial nucleus may exist, but it remains equivocal until confirmed with additional methods. Light microscopic examination of plastic sections confirmed these observations and showed further details of the organization of the primary vestibular projection to the nodulus and uvula. These results show that the region of the cerebellum densely innervated by primary vestibular afferents is smaller than previously believed.

Afferent Pathways↗