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Vertigo is an illusion of rotatory or linear movement that demonstrates a functional or lesional disturbance of the vestibular system, from periphery to central connections. According to the ANAES report (1997), benign paroxysmal positional vertical vertigo, vestibular neuronitis and Meniere's disease account for 40-50% of all mixed vertigo etiologies. Central etiologies may account for 20-40% of causes and 10-40% remain more difficult to classify, and are usually classified under the term of "peripheral vestibulopathy." These include vertigo due to neurovascular compression syndrome of the VIIIth nerve. Clinical manifestations, differential diagnosis, and treatment of the main etiologies of vertigo will be developed in this chapter. A specific section will discuss the subject of neurovascular compression syndrome of the VIIIth nerve. Even though some publications should be challenged, it appears that neurovascular compression syndrome of the VIIIth nerve might explain some cases of vertigo or chronic instability, with or without cochlear signs. The diagnosis is difficult and must be established on multiple clinical, electrophysiological and radiological arguments. A therapeutic test with antiepileptic drugs is helpful. The treatment includes these drugs as a first option but may require a neurosurgical approach if medical treatment fails.

The standard translabyrinthine approach for acoustic neuromas removal was introduced by W. House in 1964. After several years of experience the original translabyrinthine approach has been progressively modified into the current "enlarged" approach by extending the area of bone removal. This increased surgical field has made the translabyrinthine approach suitable for the removal of tumours of all sizes. We present our serie of 71 large (52) and giant (19) neuromas of the VIIIth nerve removed through a translabyrinthine approach between 1993 and 1998 at the ENT Department of Legnano.

Maturation of the cochlea and afferent auditory units is reflected by changes in VIIIth nerve compound action potential (CAP) parameters. We studied auditory nerve CAPs evoked by low-intensity stimuli in Mongolian gerbils (Meriones unguiculatus) ranging in age from 22 to 92 days after birth. The gerbil CAP development is characterized by marked changes in latency, threshold, and amplitude during the first few weeks of life. CAP latency and CAP threshold reach adult-like values at about 1 month of age. In contrast, the CAP amplitude continues to grow in size even after 2 months. This dichotomy suggests that the development of afferent auditory nerve function in the gerbil is preceded by maturation of the mechanical processes of the middle ear and cochlea.

The gold standard for control of vertigo in vestibular disorders is the translabyrinthine total VIIIth nerve section. This procedure is recommended for patients disabled by vertigo when there is severe or total loss of hearing in the involved ear. The procedure is associated with a low morbidity rate and insures a total loss of vestibular function in the operated ear.

The ability of auditory fibers in the anuran's VIIIth nerve to regenerate back into the central nervous system after their axons have been served was studied electrophysiologically and anatomically. Single unit recordings in the regenerated portion of the nerve indicate that: (1) fibers from both the amphibian and basilar papillae regenerate; (2) tuning curves of regenerated fibers, as in normal fibers, are 'V' shaped and retain their sharp frequency selectivity; (3) latency and threshold measurements of regenerated fibers are similar to values obtained in intact nerves. Filling the posterior branch of the regenerated VIIIth nerve with horseradish peroxidase indicates that fibers in this branch remain together within the nerve during regeneration and succeed in terminating in their correct target nuclei and no others.

Summary Auditory evoked potentials to ‘clicks’ were averaged from the scalps of litters of anesthetized rat pups and kittens throughout neonatal development. The potentials were shown to be from the brain stem auditory system, VIIIth nerve to inferior colliculus. At a fixed intensity and rate, peak latencies of the waves shortened with increasing age, while inter-litter variability decreased. The latencies of early waves shortened to adult values at younger ages than later waves. Increasing the intensity of stimulus at any age caused reduced latency of all of the waves; sometimes, the pattern of latencies seen at a younger age could be duplicated at an older age with a decreased intensity. Increasing the stimulus rate reduced the size of the waves, and there was return to control levels after 100 stimuli/sec in rat pups, adult rats, and cats, but not in kittens. The results are consistent with the hypothesis that significant limitations in both the immature and mature auditory system, as measured by peak latencies, occur before the VIIIth nerve. Several of the parameters studied can serve as a measure of ‘maturation’ in the auditory system, but at some ages one measure may be ‘immature’ when another is ‘mature’.

The primordium of the VIIIth cranial ganglion (otic vesicle) was extirpated on the right side of 428 embryos of Ambystoma maculatum at stage 27. Mauthner's cell (MC) develops in close association with the VIIIth nerve roots and to a lesser degree with VIIth lateral-line roots. The primary objective of the experiments was to record from a large series of animals the number of cases in which MC failed to differentiate in the absence of VIIIth root fibers. In addition, all embryos were separated (stages 3, 5, 9) into various groups and maintained continuously at different constant temperatures (5°, 8°, 10°, 14°, 18°C) until operation. The various temperature groups were then compared among themselves for any constant or significant differences with regard to the suppression of MC on the operated side. Animals were examined at stage 46. The VIIIth root fibers were completely absent in every case on the operated side. Although the VIIth lateral-line ganglia were present in all animals, root fibers failed to develop in 173 cases. This afforded an opportunity to study the influence of VIIth lateral-line roots upon the differentiation of MC, as well as the influence of VIIIth roots. Mauthner's cell was absent in 119 cases (27.8%). In 55 of these cases only VIIIth root fibers were absent; in 64 cases both VIIIth and VIIth roots were missing. The importance of VIIIth root fibers in influencing the differentiation of MC, therefore, is obvious since in 46% of those cases in which MC failed to develop absence of the VIIIth root was the only deviation from normal. The presence or absence of MC correlated with the presence or absence of VIIth lateral-line roots gives a relatively high Chi-square value of 11.461. The temperature series data are inconclusive in demonstrating a critical or optimal thermal effect upon the sequential steps affecting the differentiation of MC. If the time in early development when temperature differentials were applied is ignored, there are no consistent or significant differences among the temperature groups with regard to the suppression of MC in the absence of the VIIth–VIIIth root complex. On the other hand, if only those animals are considered that were separated at stage 9 (the majority of the animals), then there is a low degree of correlation (significance slightly above the 1% level) between greater suppression of MC in the 8° groups as opposed to lesser suppression in the 14° groups. These results on temperature influence are in need of further experimentation and analysis.