Otolaryngology–Head and Neck Surgery

Dizziness is a nonspecific symptom caused by many different pathophysiologic mechanisms. Vertigo, an illusion of movement, indicates a lesion within the vestibular system. The duration of attacks and associated symptoms helps to determine the site of lesion and likely diagnosis. Examination of the dizzy patient should include a careful assessment of gait and balance and a search for spontaneous and positional nystagmus. The vestibulo-ocular reflex can be evaluated qualitatively at the bedside with the doll's eye, dynamic visual acuity, and ice water caloric tests. Each test provides different information about vestibular function.

Computerized dynamic posturography uses a force platform that can both translate and rotate. When combined with visual stimuli, it can be used to determine the relative importance of the various sensory inputs critical for balance, namely vision, somatosensation, and vestibular sensation. Studies to date have shown several patterns of abnormalities on posturography, the best recognized being the vestibular pattern. Many patients with a high suspicion of having a peripheral vestibular abnormality (based on other information) have such a pattern. Moreover, few normal subjects have such abnormalities. Although computerized dynamic posturography does not help in localizing a lesion or determining its etiology, such testing does provide a functional measure that can be helpful in understanding a patient's ability to properly use vestibular system information. Posturography is helpful in the management of patients with suspected vestibular disorders. In addition to suggesting the presence of a vestibular system abnormality, particularly an uncompensated peripheral vestibular deficit, a bilateral peripheral vestibular deficit, or a central vestibular abnormality, computerized dynamic posturography may help guide the clinician regarding choice of treatment and counseling of patients. Further studies are required to determine the ultimate role of computerized dynamic posturography in the management of patients with vestibular disorders.

The visual system interacts synergistically with the vestibular system. A normally functioning vestibulo-ocular reflex is necessary but not sufficient for optimum visual acuity during head motion. Studies of dynamic visual acuity, the acuity achieved during relative motion of visual targets or of the observer, indicate that motion of images on the retina markedly compromises vision. The vestibulo-ocular reflex normally provides a substantial measure of stabilization of the retina during head movements, but purely vestibular compensatory eye movements are not sufficiently precise for optimal vision under all circumstances. Other mechanisms, including visual tracking, motor preprogramming, prediction, and mental set, interact synergistically to optimize the gain (eye velocity divided by head velocity) of compensatory head movements. All of these mechanisms are limited in their capacity to produce effective visual-vestibular interaction at higher rotational frequencies and velocities. It is under these conditions that vestibular deficits give rise to symptoms of oscillopsia. Patients having vestibular lesions exploit mechanisms of visual-vestibular interaction to compensate by substitution for deficient vestibular function. Thus, for accurate topographic clinical diagnosis of vestibular lesions, testing conditions should isolate purely vestibular responses. This may be done by testing reflex eye movements during passively generated rotations in darkness, or perhaps by testing during other types of motion under conditions of extreme frequency and velocity sufficient to attenuate the effects of visual-vestibular interaction. This article reviews clinical tests of vestibular function in relation to synergistic interactions with vision.

PURPOSE: State-of-the-art imaging of the normal and pathologic vestibule.

METHODS AND MATERIAL: This study is based on the experience of three French imaging centers (Val de Grâce, Bégin, and Saint-Antoine hospitals) working with 1- and 1.5-tesla magnetic resonance units and high-resolution computed tomography, and it includes a review of the literature. Computed tomography is performed with a high-resolution program, matrix 512 × 512, field of view 9.6 cm, joined 1-mm section, overlapped sections every 0.5 mm, axial and coronal sections, or reformatted images. High-resolution magnetic resonance imaging (matrix 512 × 384), field of view 18 cm, is used with fast T₂-weighted sequences (sections 3 or 2 mm thick, constructive interference in steady state, T₂-weighted gradient echo sequence three-dimensional Fourier transformation). A joined section of 0.7 mm in any direction is obtained if necessary. Superimposition of computed tomography and magnetic resonance imaging with a stereotactic technique by identification of identical anatomic points is sometimes used.

RESULTS: We review the interest and place of computed tomography and magnetic resonance imaging in the diseases of the labyrinth and internal auditory canal related to abnormal vestibular functions: inflammatory labyrinthitis, vestibular hemorrhages, sclerosing and ossifying labyrinthitis, traumatism, malformations, perilymphatic fistulas, otosclerosis, tumors, cochleovestibular neuritis, and hydrops of the endolymphatic system.

Healthy ears generate low-level sounds known as otoacoustic emissions that are produced by the normal workings of the inner ear. By placing a specially constructed probe containing an assembly of miniature microphones in the ear canal, hearing investigators can listen to these sounds. Before emissions were discovered, the only methods available to explore the ordinarily inaccessible structures of the cochlea involved invasive and, thus damaging, experiments, which could only be performed on animals. With the discovery of otoacoustic emissions, noninvasive research on the inner ear became possible, thus allowing study of the fundamental processes that determine the excellent sensitivity and fine frequency tuning that are uniquely associated with human hearing. The results of these basic experiments have made it possible to develop a number of useful clinical applications based on emissions testing. One noteworthy benefit is the use of emissions as a screening test that objectively assesses the functional integrity of peripheral processing in patients who are difficult to examine, such as infants and young children. Other applications take advantage of the test's diagnostic strength as an indicator of the sensory component of a sensorineural hearing loss. Finally, because emissions testing can be conducted rapidly and accurately under computer control, it has proved useful in the serial monitoring of ear performance in instances where a progressive hearing impairment is suspected.

The development of a standard test battery for the evaluation of vestibular function required a variety of preliminary investigations about the technical and physiologic foundations of the tests. The most important technologic development was the creation of computerized methods, including hardware and software capabilities. The designs of tests were based on physiologic and diagnostic considerations, as demonstrated in experiments on normal subjects and patients. Although time tested and sound, the available test battery satisfies only a limited number of requirements for comprehensive evaluation of vestibular function. This article describes the list of accomplishments, the state of the present limitations, and the needs for the future.

Physiologic study of the guinea pig model of endolymphatic hydrops has been used to better understand the manifestations of Meniere's disease. Quantitative vestibular function testing demonstrates some changes in the hydrops subjects, especially if an additional stress such as postural inversion is imposed. Understanding the hydrodynamic changes on the endolymphatic and perilymphatic fluids by the hydrops condition as well as postural inversion may be useful in explaining the vestibular findings. These pressure effects may alter the micromechanics of the inner ear or possibly induce a relative vascular ischemia. Auditory dysfunction is speculated to occur through similar mechanisms.

Endolymphatic hydrops is the characteristic morphopathology observed at postmortem examination of temporal bones of Meniere's disease. Surgical induction of endolymphatic hydrops in the guinea pig provides a reproducible animal model for the investigation of some effects of endolymphatic hydrops on inner ear function. Episodic and incapacitating vertigo are classic features of Meniere's disease, although very limited vestibular dysfunction has ever been described for the animal model. On the other hand, the auditory deficits peculiar to Meniere's disease, including fluctuant sensitivity losses and a peak audiogram, are also observed at different stages in the development of experimental hydrops. In future studies the model is likely to provide a means of investigating osmoregulatory function of the inner ear.

The etiopathogenesis of Meniere's disease has remained controversial since the early 1900s. Many investigators have studied the histopathology of the inner ear in patients with this disorder. Three basic pathologic mechanisms have emerged: fibrosis of the endolymphatic sac and vestibular epithelia, altered glycoprotein metabolism, and inner ear viral infection. This article reviews the current understanding of these three basic pathologic processes.

This article reviews current studies on inner ear blood flow, discusses their relevance to the maintenance of normal homeostasis of the inner ear, reports for the first time clear changes in fundamental properties of cochlear blood flow in the chronic hydropic ear, and describes the potential of applying laser Doppler flowmetry technology to the measurement of inner ear blood flow in human beings. Studies of the guinea pig in which perfusion pressure is varied demonstrate a broad range of autoregulatory capabilities of the inner ear vasculature. Gain factors range from 0.76 and higher for recovery for less than 1 minute of modified perfusion pressure. This is significantly greater than reports obtained for brain autoregulation. In a series of four investigations of cochlear blood flow in the hydropic ear in guinea pigs, a decreased responsiveness to electrical stimulation and direct stimulation of the superior cervical ganglia was found, indicating a change in sympathetic control of cochlear tone. Reduced vasomotion was observed, and autoregulatory capabilities were reduced. In human investigations, changes in cochlear blood flow were demonstrated with direct electrical stimulation of the round window and warm water irrigation of the ear canal, but not with carbogen breathing. Increased cochlear blood flow was observed with increased systemic blood pressure, and a remarkable decrease in cochlear blood flow was observed with the application of 1:10,000 epinephrine to the round window. These observations indicate the potential for development of laser Doppler flowmetry technology in the diagnosis and treatment of inner ear vascular disorders, and the animal Investigations suggest that changes may occur in the chronic hydropic ear that compromise autoregulation and thus increase the sensitivity of the hydropic ear to other stress factors. Treatments can be found to modify such changes in vascular tone.

Vertigo is the most common symptom of transient ischemia within the vertebrobasilar system. Episodes typically come on abruptly and last minutes. Although there are usually associated symptoms, isolated attacks of vertigo can occur. Vertigo is also a common symptom with brain stem and cerebellar strokes. Isolated cerebellar infarction can mimic peripheral vestibular disorders because vertigo and imbalance are the main symptoms with both disorders. Modern neuroimaging techniques have markedly improved diagnostic capabilities.

The rationale, indications, and surgical results of microvascular decompression for the treatment of vertigo are reviewed, and a critical analysis is made. The syndrome of disabling positional vertigo is discussed. It is concluded that (1) vascular compressive vestibular neuropathy may exist, (2) the current published diagnostic criteria for this disorder are insufficient to firmly establish the diagnosis, and (3) further work delineating this syndrome should be undertaken.

Paraneoplastic cerebellar degeneration typically begins with rapidly progressive ataxia of the trunk and extremities. Antineuronal antibodies are found in about half the patients. The most specific autoantibody is an anti-Purkinje cell antibody found in women with gynecologic tumors. Even after the tumor is removed, the cerebellar deficit persists in most patients.

This article reviews the impact of metabolic disorders on vestibular function. Diabetes mellitus is a disorder of glucose metabolism that can be associated with vestibular dysfunction. Vertigo can be alleviated by diet management in many cases. Elevated levels of blood lipids have been implicated in cochleovestibular disorders. Treatment with a lipid-lowering drug has resulted in improved auditory and vestibular function in a placebo-controlled trial. Hypothyroidism may affect different parts of the vestibular system depending on the severity and duration of thyroid deficiency. Severe congenital hypothyroidism can cause central vestibular disorders affecting the cerebellum, whereas mild hypothyroidism may result in peripheral vestibulopathy. Endogenous alterations in concentrations of estrogen and progesterone in the premenstrual syndrome or with the use of exogenous hormones such as oral contraceptives may trigger vertigo. Metabolic evaluations for unexplained vertigo should include a lipoprotein profile, with cholesterol and triglyceride levels, glucose tolerance test, and thyroid hormone measurements. Nutritional and drug therapy may be useful to reverse the vestibular dysfunction.

A great deal of the controversy associated with perilymph fistula is due to the lack of a sensitive, specific way of detecting and thus diagnosing one. The existing subjective, clinical observations need to be replaced with an objective, scientific methodology having higher specificity and sensitivity for the detection of perilymph fistula. Three detection methods presently under development are presented here. One uses a miniendoscope to observe the middle ear. This procedure is less traumatic than inspection with tympanotomy. Thus it is less likely to create artifacts that can be mistaken for a fistula leakage. The “yes-no” observation decision is to be replaced with a graded quantitative measure. The second method concentrates on detected leakage from inner to middle ear. β2-Transferrin, a unique endogenous substance found in perilymph and cerebrospinal fluid, can be detected with one- or two-dimensional gel electrophoresis and immunoblotting. The third method is a system identification fistula test. It measures a change in a physiologic response that is caused by the presence of the fistula. Classic biophysical models of the vestibular end organs can be used to predict the dynamics of responses to systems identification stimuli.

My clinical and laboratory observations support the theoretical concept that the mechanism of typical nystagmus, and most forms of atypical transient nystagmus, is hydrodynamic drag by gravitating free densities-most commonly displaced otoconia-in the endolymph of a semicircular canal; and that these “canaliths” have a significant mechanical advantage, by virtue of the canal/ampulla cross-sectional differential, over densities acting directly on the cupula. Positional vertigo related to apparent canalithiasis (benign paroxysmal positional vertigo) is a common cause of incapacitation. The profile of the concomitant nystagmus localizes the semicircular canal involved. The canalith repositioning procedure, appropriately administered and targeted according to the observed nystagmus, provides a highly effective means for control of symptoms and a valuable resource for diagnostic evaluation of the more complex case. Surgery is rarely indicated.

Because the cause of vestibular neuritis is unknown, this disorder is best understood as a constellation of characteristic clinical symptoms and signs. The differential diagnosis includes peripheral otologic disorders, including Meniere's disease, perilymph fistula, and vestibular atelectasis; and central disorders, including vascular insufficiency, acoustic neuroma, migraine equivalent, paraneoplastic syndrome, metastatic carcinoma, and multiple sclerosis. The site of lesion, as evaluated by clinical signs and symptoms, is controversial because concomitant central nervous system abnormalities have been described. The histopathology of temporal bones from persons who in life had symptoms characteristic of vestibular neuritis demonstrates degeneration of branches of the vestibular nerve and the neuroepithelium of vestibular end organs. Possible causes of vestibular neuritis include viral or other infectious agents and vascular or immune-mediated disorders. The natural history of this disorder is variable. In some patients complete recovery of acute signs and symptoms, including loss of vestibular response, is seen, whereas in others permanent changes have been reported. Initial treatment is generally symptomatic only. Patients with poor recovery may benefit from vestibular rehabilitation or, occasionally, from surgical intervention. The elucidation of the pathogenesis of vestibular neuritis and the development of logical guidelines for individual rehabilitation are needed.

Although the use of vestibular exercises for patients with persistent vertigo and dysequilibrium has received some attention for many years, organized vestibular rehabilitation therapy programs have only recently been introduced. The benefits of such programs are becoming widely accepted. They typically involve a three-pronged approach: habituation exercises designed to facilitate central nervous system compensation by extinguishing pathologic responses to head motion, postural control exercises, and general conditioning activities. This article will describe the programmatic approach to vestibular rehabilitation, emphasizing selection criteria and reviewing results that may be anticipated when this treatment modality is used in a variety of patient populations.

This study attempts to characterize the residual vestibular function remaining after incomplete supralabyrinthine vestibular neurectomy performed for disabling vertigo. Patients with bilateral vestibular neurectomy had preserved horizontal vestibulo-ocular reflexes in response to high angular accelerations with gain enhancement over time. A torsional down-beating spontaneous nystagmus and an important tilt of the subjective vertical were observed when the remaining eighth nerve was sectioned after homolateral incomplete supralabyrinthine vestibular neurectomy. These findings suggest that a reorganization of vestibular reflexes may occur after incomplete supralabyrinthine vestibular neurectomy if afferents of the inferior vestibular branch are partially spared. The vestibular function after incomplete supralabyrinthine vestibular neurectomy does not affect the postoperative control of vertiginous attacks and may have positive effects in case of deterioration of the contralateral inner ear.