HISTORY

Charcot, in 1874, and later Frazier⁸ initially described neurectomy of the vestibulocochlear nerve. Subsequently, in 1928, Dandy⁹ strongly advocated intracranial sectioning of the eighth cranial nerve for paroxysmal vertigo symptoms. Although he noted that the procedure often was successful for relieving troubling vertigo, patients typically had a complete hearing loss in the operated ear. McKenzie,¹⁰ in 1931, developed a selective neurectomy technique, preserving auditory function in some cases. Some 30 years later, House¹¹ developed the middle fossa and translabyrinthine approaches for vestibular nerve sectioning. Later modifications by Fisch and Glasscock and colleagues^12–14 refined these approaches. The importance of preserving not only the cochlear nerve, but also the labyrinthine blood supply as a critical premise for hearing preservation was realized. Silverstein and colleagues^15,16 later described in detail the complex interrelationship of the vestibular and cochlear nerve fibers in the cerebellopontine angle, allowing for even more selective neurectomy near the root entry zone in the brainstem. Over the last 50 years, Hitselberger and his colleagues can be credited with performing vestibular nerve section procedures on hundreds of patients with peripheral vestibular disorders.¹⁷ Today, successful vestibular nerve section relies on the anatomic and surgical principles developed by these pioneers.

DIAGNOSTIC CONSIDERATIONS

Selecting an appropriate surgical intervention for patients with peripheral vestibular disorders is challenging. In considering such therapy, a diagnosis must first be rendered or, minimally, an affected ear must be identified. Although a detailed discussion regarding the diagnosis and management of vestibular disorders is beyond the scope of this chapter, an understanding of the various vestibular disorders is crucial to identifying a correct diagnosis and making an adequate treatment recommendation.^18,19 Establishing the correct diagnosis may be difficult sometimes, and can require the input from various professionals in differing disciplines. Vertigo is the cardinal symptom of a vestibular system disorder. It is also important to recognize that many cases of dizziness are not related to the vestibular system at all, and dizziness without vertigo is common. When vertigo is absent, the diagnosis of vestibular disorder should be carefully scrutinized. Although the presence of vertigo can be of either central or peripheral origin, most cases of vertigo arise from the peripheral vestibular apparatus (SSC, otolithic organs, or vestibular nerves).

Although most of these peripheral vestibular disorders manifest to the clinician with a clear clinical picture, occasionally differentiation from the common central causes of vertigo is difficult. Differentiation among the peripheral and central varieties of vertigo takes on even greater significance when ear-specific therapies are being contemplated. When peripheral deafferentation is considered in the treatment regimen, defining the peripheral cause and the affected labyrinth is crucial. The most common causes of peripheral (or ear-related) vertigo in adult patients include benign paroxysmal positional vertigo (BPPV), Meniere’s disease, and vestibular neuronitis. More recently, superior semicircular canal dehiscence (SSCD) syndrome has become more frequently recognized.^20,21 Common central causes of vertigo include migraine-related dizziness (also known as migraine vestibulopathy²²), transient ischemic attack, and demyelinating disease such as multiple sclerosis and stroke.

In nearly all patients with vertigo, a careful history, physical examination, and appropriate laboratory and radiologic testing can reveal the correct diagnosis. A minimal test battery usually includes comprehensive audiometric testing, imaging of the temporal bone and brain, and laboratory evaluations, which may include selective vestibular function testing (see section on preoperative testing).

Meniere’s disease is characterized by episodic vertigo that lasts minutes to hours with associated, fluctuating aural symptoms, including hearing loss, tinnitus, and pressure. Audiometric testing characteristically reveals a low-frequency sensorineural hearing impairment. In contrast, BPPV is characterized by brief (<20 seconds), position-induced attacks of vertigo in the absence of other auditory symptoms. Symptoms in these patients can be reproduced with the Dix-Hallpike maneuver, which often reveals a torsional nystagmus when the head is positioned with the affected ear in a gravity-dependent position. By contrast, vestibular neuronitis typically is considered when patients experience a single, prolonged (i.e., days) attack of vertigo, without associated auditory symptoms, which is followed by a period (i.e. days to weeks) of motion intolerance or BPPV or both. SSCD syndrome is characterized by symptoms of vertigo or dizziness induced by sound or pressure applied to the affected ear or via a Valsalva maneuver.^20,21 Typically, auditory symptoms include hearing loss, pressure, and occasionally pulsatile tinnitus. In this disorder, audiometric testing commonly reveals a conductive hearing loss with preserved acoustic reflexes.

Occasionally, the previously described peripheral vestibular disorders are not easily recognized, and further testing is needed, usually vestibular function testing and imaging studies. Vestibular function testing in the form of electronystagmography (ENG) can help identify (1) nystagmus associated with BPPV, (2) pressure-induced nystagmus in SSCD syndrome, and (3) reduced responsiveness to caloric irrigations after vestibular neuronitis or prolonged exposure to Meniere’s disease. Rotational chair testing can be useful in assessing a patient’s level of central compensation after a peripheral vestibular lesion, but is seldom helpful in localizing an affected ear. Vestibular-evoked myogenic potential (VEMP) testing can help identify inferior vestibular nerve dysfunction in the setting of a normal caloric response on ENG. VEMP testing can also be useful in patients with suspected SSCD syndrome in which thresholds are reduced in the affected ear. Although these tests can be a useful adjunct in making the diagnosis, it remains crucial to rule out central vestibular disorders, especially when deafferentation is being contemplated. In addition to a careful history and physical examination, magnetic resonance imaging (MRI) is often useful to help exclude multiple sclerosis, stroke, and tumors such as an acoustic neuroma.

Migraine-related dizziness is common and can masquerade as any of the aforementioned vestibular disorders.^22,23 It is characterized by episodic vertigo or dizziness that can last seconds to hours or even days. It may or may not be associated with headache, visual, or auditory symptoms. When retro-orbital headache and visual scotoma are associated with vertigo attacks, the diagnosis is seldom difficult. Symptoms often may abate following sleep, adding credence to the diagnosis. Patients with migraine-related dizziness frequently relate a history of motion or sound intolerance, however, in periods between attacks similar to individuals with BPPV and SSCD syndrome. Migraine-related vertigo may also be associated with a classic Meniere’s disease history, which can make distinguishing these disorders extremely difficult, especially when there is no hearing loss. Patients with migraine-related dizziness can have ENG abnormalities and can respond to diuretic therapies similar to patients with Meniere’s disease.²⁴ All otologists who manage patients with vertigo should have a very high index of suspicion for this disorder. When patients have episodic vertigo in the absence of objective evidence of hearing loss, migraine-related dizziness must be ruled out before considering ear-specific therapy.

TREATMENT OF VESTIBULAR DISORDERS: AN OVERVIEW

When the correct diagnosis has been made, medical management should be used in an attempt to control unwanted symptoms before considering ear-specific therapies, destructive therapies, or both. “Control of symptoms” is a personal judgment made by the patient and the physician, and can differ among individuals. In one patient, an occasional attack of vertigo may be unacceptable, whereas in another individual, frequent attacks may have little consequence to their daily life. The severity of attacks may be a more compelling reason for intervention than just the frequency of the attacks. Physicians are left to contemplate these interventions with their patients in the context of this varying degree of disability. When diagnostic uncertainty persists, further medical evaluations are often necessary before considering ear-specific therapies.

For Meniere’s disease, medical therapies can be conveniently divided into either prophylactic or abortive treatments. Prophylactic interventions generally include dietary modifications and pharmacologic therapies with diuretics, vasodilators, antihistamines, and immune modulators. Abortive treatments usually include some regimen of vestibular suppressants. These various medical therapies are usually efficacious in controlling episodic, spontaneous vertigo attacks in most patients with only a few requiring further treatment. Vestibular physical therapy can be a useful adjunct for inducing compensation in individuals with significant motion intolerance resulting from vestibular loss. Vestibular physical therapy does not treat or prevent spontaneous attacks of vertigo in patients with Meniere’s disease. When medical interventions fail to control symptoms, ear-specific therapies should be contemplated.

Ear-specific therapies include destructive and nondestructive therapies. Destructive therapies are therapies that induce either partial or total vestibular deafferentation with or without hearing loss. Nondestructive therapies include endolymphatic sac procedures, intratympanic steroids,²⁵ and transtympanic pressure therapy²⁶ in patients with Meniere’s disease. For patients with SSCD syndrome, tympanostomy tube placement to control pressure-induced symptoms could also be considered as a nondestructive therapy. Canalith repositioning maneuvers are ear-specific therapies that often resolve unwanted positional vertigo in patients with BPPV.

As a last resort, destructive or deafferentation procedures are considered for patients with symptoms that remain refractory to the aforementioned approaches. Deafferentation can be accomplished by either chemical or surgical means, and can be directed at the receptors of the inner ear, the vestibular afferent fibers to the brain, or some combination thereof. When the labyrinth remains intact, these procedures can be undertaken with the intent of hearing preservation. Hearing-preserving total labyrinthine deafferentation procedures include vestibular nerve sectioning^5,27 and intratympanic gentamicin.²⁸ For patients with BPPV, partial deafferentation can be accomplished by partitioning of the affected posterior SCC while maintaining hearing.²⁹ Likewise, patients with SSCD can achieve control of symptoms with surgery directed at occlusion of the affected superior SCC, often with improvement in hearing.³⁰ When hearing is not an issue, transmastoid labyrinthectomy or translabyrinthine vestibular nerve sectioning can reliably provide comprehensive vestibular deafferentation.