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.

PREOPERATIVE TESTING

Before vestibular denervation procedures are considered, a thorough functional and anatomic evaluation of the patient’s auditory and vestibular systems is indicated.

SURGICAL PROCEDURE

Surgery is performed under general anesthesia. The patient is placed on the operating table in a supine position; the table is rotated to allow for table manipulations and to permit the surgeon to sit comfortably with knees under the table. A postauricular sterile area of about 3 cm is prepared and draped off. This area should be extended slightly superior to the auricle to provide adequate exposure of the middle fossa plate. The high-speed drill with various burrs and suction-irrigation with sterile saline are on the field. Monopolar and bipolar electrocautery are available. Today, CN VII monitoring equipment and the operating microscope are used for every case. The facial nerve monitoring electrodes are inserted into the lateral portions of the orbicularis oris and orbicularis oculi muscles and covered with a sterile, impermeable drape. Also, a small abdominal area left of the umbilicus is prepared for harvesting an abdominal fat graft. Informed consent, audiogram, and ENG are reviewed to confirm the correct patient and laterality of the procedure. Generally, a first-generation or second-generation cephalosporin is given before incision for broad antimicrobial prophylaxis. In cases of β-lactam allergy, other agents may be used.

An incision is made approximately 1 cm above and behind the postauricular crease and follows the contour of the auricle (Fig. 37-1). A plane is established in the galea aponeurotica lateral to the temporalis muscle, and the auricle is turned forward. This layer is best established directly over the temporalis fascia superiorly and over the mastoid periosteum inferiorly. The musculoperiosteal flap is incised separately and elevated off the mastoid cortex with the help of a periosteal elevator or monopolar electrocautery. This flap is moved forward to the level of the posterior external auditory canal and mastoid tip, and subsequently fixed with a large self-retaining retractor. Care is taken not to create an opening in the external auditory canal skin because this can provide a route for cerebrospinal fluid leakage postoperatively.

FIGURE 37-1 Postauricular skin incision about 2 to 3 mm behind the aural crease with an extension superior to the auricle.

The high-speed drill with a large cutting burr and constant suction-irrigation is used to perform a cortical mastoidectomy. The posterior aspect of the external auditory canal wall and the bone overlying the inferior temporal lobe dura is thinned, and the sigmoid sinus is skeletonized (Fig. 37-2). The mastoid antrum, horizontal SCC, and short process of the incus are brought into clear view. For the sigmoid sinus, an eggshell of bone is usually left over the vein wall to protect it from manipulation during deeper dissection. Some surgeons leave a larger bony island over the sinus to compress it medially and gain better exposure of the medial temporal bone. The sinodural angle is opened as far posteriorly on the cortex as possible. Because the vestibule lies medial to the facial nerve, a tangential view is facilitated by this additional exposure.

FIGURE 37-2 Surgical view after cortical mastoidectomy has been performed. Facial nerve is visualized in its entire mastoid segment. Facial recess is opened (not shown). Sigmoid sinus and bony middle fossa plate have been visualized. Bony labyrinthine capsule has been exposed.

At this point, the descending mastoid segment of the facial nerve is identified, and the presigmoid posterior fossa dura can be thinned. Generally, the nerve is identified while opening the facial recess. This access to the middle ear is used later for eustachian tube closure to prevent cerebrospinal fluid egress. The incudostapedial joint is divided, and the incus is removed. Care should be taken not to disrupt the stapediovestibular ligament because this may provide another route for cerebrospinal fluid leakage into the middle ear. It also may be useful to transect the tensor tympani tendon for better access to the eustachian tube lumen. The mastoid segment of the facial nerve is followed inferiorly toward the stylomastoid foramen. This step is necessary for wide access to the ampullated end of the posterior SCC and, more medially, the inferior trough below the IAC. The three SSCs of the vestibular labyrinth are skeletonized.

Before labyrinthectomy and subsequent permanent hearing loss, the operative consent, audiogram, and ENG are reviewed again as an additional level of safety. The labyrinthectomy is initially carried out using a 3 or 4 mm cutting burr. First, the horizontal SCC is half-opened on its superior border from the ampulla anteriorly to the intersection with the posterior SCC. The horizontal SCC is initially only half-opened to protect the external genu of the facial nerve inferiorly. Next, the posterior SCC is opened and traced superiorly to its confluence with the superior SCC (i.e., common crus) (Fig. 37-3). The common crus may be followed directly toward the vestibule (Fig. 37-4). The superior SCC is also opened along the entire path to the ampulla. During this maneuver, care is taken not to damage the temporal lobe dura, which usually lies in very close approximation to the superior SCC lumen.

FIGURE 37-3 Lateral and posterior semicircular canals have been opened. Posterior canal can be traced superiorly and medially to common crus with superior semicircular canal.

FIGURE 37-4. Superior semicircular canal has been opened. Also, common crus of superior and posterior semicircular canals is now visible. Vestibule has been carefully opened, and soft tissue can be stripped out using a right angle hook.

FIGURE 37-5. Vestibule has been opened. Care must be taken when drilling the ampullated part of the posterior semicircular canal because it is located medial to the mastoid segment of the facial nerve.

FIGURE 37-6. Skeletonizing the bony internal auditory canal (IAC).

FIGURE 37-7. Establishing the contents of internal auditory canal. Superior and inferior vestibular nerves have been avulsed. Vertical crest (Bill’s bar) can be seen with the facial nerve underneath. The cochlear nerve can be found inferior and anterior within internal auditory canal.

FIGURE 37-8. Both branches of vestibular portion of CN VIII have been avulsed. Cochlear and facial nerves are visible in anterior compartment of internal auditory canal.

The superior and posterior surfaces of the external genu of the facial nerve are now carefully identified to facilitate dissection of the posterior SCC ampulla, which lies more medially. Inferior dissection in the retrofacial air cell tract beyond the posterior SCC ampulla is unnecessary in this procedure, and might reveal the jugular bulb. When the three SCC ampullae and the common crus have been opened to the vestibule, the spherical and elliptical recesses of the vestibule and the endolymphatic duct can be appreciated. At this point, all soft tissue elements of the membranous labyrinth are removed. This step would be the normal end point for postganglionic, transmastoid labyrinthectomy (Fig. 37-5).

A key factor for successful TLVNS is thorough dural decompression of the IAC from the porus acusticus to vestibule with precise identification of the facial nerve at the meatal foramen and in its labyrinthine segment. Beyond the labyrinthectomy, the approach to the IAC is aligned by recognizing that the lateral IAC boundary is the vestibule and the three SCC ampullae. The subarcuate artery courses through the arch of the superior SCC within the petromastoid canal, typically superior to the IAC. Also, the IAC lies in a similar plane as the external auditory canal. With these anatomic relationships in mind, the presigmoid posterior fossa dura is decompressed medially until the porus acusticus dura is identified.

When the IAC dura is identified medially, further anterior dissection superior and inferior to the canal allows for the creation of “troughs.” These troughs should create approximately 270 degrees of dural exposure over the medial two thirds of the IAC (Fig. 37-6). The superior trough is bounded superiorly by the temporal lobe dura and inferiorly by the IAC dura. The inferior trough is bounded superiorly by the IAC dura and inferiorly by the cochlear aqueduct and jugular bulb. Frequently, air cells are encountered in the superior trough above the IAC. In the inferior trough, dissection usually reveals the cochlear aqueduct as a fibrous tissue–containing tract that elutes cerebrospinal fluid. Inferior dissection below the aqueduct should be avoided because the lower cranial nerves can be at risk in this region. Finally, dural decompression of the lateral aspect of the IAC should proceed to identify the vertical and the horizontal crests of the IAC, and subsequently the facial nerve in its labyrinthine segment.

The vertical crest (or Bill’s bar) is identified by following the superior IAC dura laterally to the vestibule. The superior vestibular nerve can also be traced to the ampulla of the superior SCC. The vertical crest lies anterior to the superior vestibular nerve. When the vertical crest is identified, emanating medially off the central portion of the superolateral end of the IAC, it is anticipated that the labyrinthine segment of the facial nerve will be just anterior to this structure. The labyrinthine segment is partially identified for confirmation. When bisecting the posterior wall of the IAC in its lateral aspect, the horizontal or transverse crest can be identified. This crest separates the superior and inferior vestibular nerve bundles as they exit the labyrinth.

After drilling is complete, bone chips are removed, and the dura is opened. Dural opening is accomplished via sharp dissection. The safest way to identify the intradural facial nerve is by careful palpation of Bill’s bar with visualization of the labyrinthine segment. The superior vestibular nerve is avulsed from its labyrinthine attachment, and the soft tissue plane between the vestibular and facial nerves is developed. The inferior vestibular nerve is transected similarly and dissected medially (Fig. 37-7). Scarpa’s ganglion lies approximately midway within the IAC portion of the nerve. If pathologic assessment is needed, a portion of the nerve is removed and sent to the laboratory (Fig. 37-8). Although the cochlear nerve may also be sectioned, this action would preclude its use in future cochlear implantation if that opportunity arises.⁴¹

Closure is accomplished by first plugging the eustachian tube and then closing the dural defect and wound. The eustachian tube is addressed through the facial recess by placing a piece of absorbable knitted fabric (Surgicel) deeply in to the tubal lumen. Secondarily, pieces of muscle usually from the temporalis are packed into the eustachian tube and middle ear up to the facial recess opening; another sheet of Surgicel holds this in place. The dural opening is closed by careful packing with strips of abdominal fat placed partly through the opening.⁴² With such a small defect, a watertight closure is usually attained with a few carefully placed pieces. A titanium mesh placed over the mastoid cortex opening is often helpful to bolster the fat in place.⁴³ The wound is closed in layers with an interrupted absorbable suture, and a firm mastoid dressing is placed.

POSTOPERATIVE CARE AND FOLLOW-UP

The patient is watched in the intensive care unit for a day with hourly neurologic checks and then is moved to a step-down room when neurologic stability is ensured. If an abdominal wound drain was used, this is removed on postoperative day 1. Antibiotics are discontinued after 24 hours so as not to promote infection with resistant organisms. Patients are encouraged to sit up and dangle their legs off the side of the bed on the 1st or 2nd postoperative day, and to begin ambulation with help as soon as possible. Ambulation and activity are usually limited by the degree of vertigo, nausea, and vomiting. These symptoms are usually controlled medically with vestibular suppressants, such as droperidol, diazepam, meclizine, and dimenhydrinate. When static compensation is sufficient, ambulation is usually possible with some assistance. At this point, head movements still elicit significant vertigo and are usually avoided. Discharge is possible when the patient is able to ambulate and tolerate a diet; however, driving is contraindicated until head movement does not cause dizziness. This level of activity usually requires dynamic compensation to occur. This process can take weeks to occur, and may require a course of vestibular rehabilitation therapy to become complete.³¹

The rate of static compensation for vertigo while in the hospital is predicted by the severity of the postoperative nystagmus. Horizontal spontaneous nystagmus is evident in all three directions of gaze (third-degree nystagmus) on the 1st or 2nd postoperative days. According to Alexander’s law, as the level of static compensation increases as a result of alterations in the vestibular nuclei tonic discharge rate, nystagmus becomes evident only in central and contralateral gazes (second-degree nystagmus). When further compensation occurs, nystagmus may be evident only on contralateral gaze (first-degree nystagmus). This level of nystagmus usually coincides with the patient’s ability to ambulate and readiness for discharge around the 5th to 7th postoperative day.¹⁸

COMPLICATIONS

Complications seen with TLVNS may include cerebrospinal fluid leak, meningitis, and facial paralysis.^6,36,44 Facial paralysis can be considered the consequence of working in an area in which the nerve is anatomically at risk. Avoidance is the best solution to this problem: the surgeon should be certain of the nerve’s location and treat it with respect.⁴⁵ Postoperative steroids or limited decompression of the nerve, particularly in the labyrinthine segment, may be useful in preventing sequelae when the nerve is known to have been traumatized. When fever and meningismus occur, a lumbar puncture is performed, and appropriate antibiotic coverage is instituted to treat bacterial meningitis. This complication is rare.

Cerebrospinal fluid leakage occurs in less than 5% of TLVNS cases using the previously described techniques. This low incidence is likely due to the limited dural opening needed for this procedure and careful closure. If wound leakage occurs, this can be managed with simple oversewing at the bedside. If rhinorrhea occurs, this is managed with a firm pressure bandage, head of bed elevation, and lumbar subarachnoid drainage for 5 days.⁴⁶ If resolution of the leak is not seen after aggressive drainage, the wound is explored, and the adipose plug is readjusted.

RESULTS AND LITERATURE OVERVIEW

TLVNS is successful at relieving spontaneous attacks of vertigo in 75% to 95% of patients with Meniere’s disease; it is substantially less successful in patients with vertigo not related to Meniere’s disease.^36,47 These findings suggest that our ability to diagnose the disorder correctly as one of the peripheral vestibular apparatus or ability to induce stable and complete central vestibular compensation remains imperfect.^5,6,32

CONCLUSION

TLVNS is a highly effective approach for achieving complete surgical deafferentation in patients with refractory vertigo from Meniere’s disease and other peripheral labyrinthine disorders. Patients should be carefully selected for this procedure and be willing to give up their residual hearing in the affected ear for vertigo control. They should be aware that deafferentation may be a tradeoff between relief of spontaneous vertigo at a cost of unsteadiness and imbalance. Although compensation is common among young and healthy patients, elderly patients may not be as tolerant. When carefully performed, TLVNS is the gold standard procedure for peripheral deafferentation, and can be used in patients who have failed previous medical and surgical attempts at controlling symptoms. Although complications can occur, they are uncommon and mostly not serious.