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Vertigo

Vertigo - Medical and Surgical Treatment, March 1998 Article
MEDICAL AND SURGICAL TREATMENT OF VERTIGO
Michael J. LaRouere, M.D.
Michael D. Seidman, M.D.
Jack M. Kartush, M.D.

INTRODUCTION

Vertigo is a term used to describe the hallucination of motion although the subject is stationary. The patient suffering from vertigo often uses the term "dizzy" to describe this sensation. However, it can also refer to such feelings as lightheadedness, unsteadiness, confusion, giddiness, or nausea.

It is the purpose of this chapter to discuss the medical and surgical treatments of vertigo. It is expected that the reader has a general knowledge of the anatomy and physiology of the vestibular system.

The prevalence of vertigo is difficult to ascertain. Disequilibrium has been found to be the first or second most common diagnosis in the short-stay hospital diagnosis related groups (DRG's) with an average hospital stay of 4 days.1 The National Health Interview Survey Supplements on Aging has found that 18% of people over the age of 65 and 25% over the age of 75 have falls.2 When asked, "does dizziness prevent you from doing things you otherwise could do?" 34% of the population between 65- 74 answered yes increasing to 37% over the age of 75. This would place 12.5 million persons over the age of 65 as having serious dizzy complaints.2 National Ambulatory Medical Care Survey in 1981 found the most common presenting symptom in patients 75 years or older was dizziness.3 This information coupled with the fact that in 1980 it was estimated that 11% of the population was age 75 or older adds to the number at risk for vertiginous disorders. This number is expected to increase to nearly 21% by the year 2030.5

CAUSES OF VERTIGO

I.PERIPHERAL CAUSES OF VERTIGO

Meniere's Disease

Vertigo is most commonly caused by disease of the peripheral vestibular system. Prosper Meniere (1861) expanded the work of Pierre Flourens and described an otogenic disorder, erroneously referred to as a triad, consisting of four symptoms: vertigo, tinnitus, fluctuating sensorineural hearing loss and aural fullness.6

Meniere's disease usually begins between the ages of 20-60 years and is estimated to affect 2.4-4-8 million Americans.7 Typically the disease is unilateral, however up to 40% of patients develop symptoms in the opposite ear.19 Clinically, Meniere's disease is characterized by the sudden onset of vertigo often accompanied by pallor diaphoresis, nausea and vomiting. The attacks are usually associated with tinnitus and/or aural fullness. The episodes may last from 20 minutes to several hours. Rarely, some patients may experience explosive attacks precipitating a fall. These drop attacks, termed Crisis of Tumarken or utricular crises, usually occur in the later stages of the disease.

More than a century has passed, there continues to be ambiguity as to the pathophysiology of this disorder. Schuknecht10 states that Meniere's disease is a symptom complex caused by different diseases that share the same pathophysiology: endolymphatic hydrops. Hydrops, an increase in endolymphatic fluid, is thought to result from endolymphatic sac dysfunction (decreased resorptive capabilities) secondary to infection, congenital hypoplasia, trauma, inflammatory causes or an idiopathic etiology. Schuknecht classifies Meniere's disease as an idiopathic endolymphatic hydrops. He has proposed a five step mechanism that leads to the development of Meniere's disease. 1. Decreased endolymph resorption: This may be caused by labyrinthitis, trauma or hypoplasia. 2. Endolymphatic hydrops: occuring because of over accumulation of endolymph which distorts Reisner's membrane. 3. Membrane rupture: Endolymph then mixes with perilymph which temporarily paralyzes the auditory and vestibular system. 4. Healing of ruptures: The breaks of Reisner's membrane heal thus allowing the entire process to repeat itself. 5. Distortion and atrophy: With disease progression, permanent changes in the membranous labyrinth occur which cause persistent disequilibrium and/or hearing loss.12

Vestibular Neuronitis

Vestibular Neuronitis is characterized by the sudden onset of disabling vertigo often associated with nausea and vomiting without auditory symptoms. Typically the onset of symptoms occur after an upper respiratory tract infection. Vestibular neuronitis most often affects patients in the 3rd to 5th decades without a sex predilection. Vertiginous symptoms are often worse with head motion. Clinically, horizontal nystagmus toward the uninvolved ear may be detected during the acute phase. Caloric testing typically reveals a reduced response in the involved ear. Routine audiometry is usually normal. Recovery is generally expected within one to three months.

Histopathologic studies have suggested involvement of the superior vestibular nerve and vestibular ganglion often with little or no involvement of the actual endorgan. Infection has long been consider a causative factor in vestibular neuronitis.30 There has been little success in documenting a viral etiology, however, intracytoplasmic particles have been recently found in human vestibular ganglia. These are thought to be dormant forms of a virus and may, when activated, produce infection with resultant inner ear disease.29,33 Other causes such as occlusion of the anterior vestibular artery, cerebellar infarctions, and acute diabetic neuropathy have been implicated in the etiology of vestibular neuronitis.31 Toxic and allergic causes are also thought to play a role in the disease process.(ref)

It has been claimed that vestibular neuronitis affects only the vestibular portion of the VIIIth cranial nerve and that the cochlear portion is left unaffected. However, Rahko(ref) found that the involved ear has a 14-24 dB SPL threshold difference compared to the unaffected ear at 20 kHz implicating some degree of damage to the auditory system in patients with vestibular neuronitis.

Benign Positional Vertigo (BPV)

Benign positional vertigo (benign paroxysmal positional vertigo) was first described by Barany in 1921 as a brief violent

vertiginous episode occurring within seconds after a change in

head position. Usually the attacks resolve if the patient remains in that position.36 In 1981, the Research

Committee for Peripheral Disorders in Japan proposed diagnostic criteria for BPV. These include: 1. Whirling vertigo induced by a specific head position or movement, 2. Characteristic burst of positioning nystagmus which is rotary in nature, fatiguable and occurs within seconds after position changes, 3. Exclusion of central nervous system disorders, cervical disorders and cochlear disorders associated with vertigo.38 The nystagmus is typically induced by turning the involved ear downward. Although the nystagmus is usually esotropic and torsional to the direction of the down turned ear, Stahle39 noted that the nystagmus pattern can vary. Calorics are normal in over 2/3 of the patients.(ref) In many series, BPV is the most frequent cause of vertigo. BPV is most commonly seen in people over the age of 40 and females out number males 1.6:1.37 The process lasts for weeks to months with spontaneous recovery in 90%. It is possible that these episodes may recur.39 Longridge and Barber40 have demonstrated bilaterality in up to 15% of affected individuals. The etiology of BPV has been a source of controversy. Baloh37 studied 240 cases of BPV and found that the most common etiology was idiopathic (118/240), followed by post-traumatic (43/240), vial neurolabyrinthitis (37/240) and miscellaneous (42/240). The pathophysiology has been best documented by Schuknecht. He observed basophilic deposits in the cupula of the posterior semicircular canals in two patients with BPV.42 He proposed that otoconia are released from a degenerating utricular macula and settle on the cupula of the posterior canal, causing it to become heavier than the surrounding endolymph.43

Perilymphatic Fistula

A perilymphatic fistula is the result of an abnormal communication between the inner and middle ear spaces. It generally occurs as a result of stapedectomy, head trauma, barotrauma, chronic ear surgery, congenital anomalies, or spontaneously.(Seltzer and McCabe) Because the presenting symptomsare similar to other otologic disorders and the inability to formally diagnose a perilymph fistula, short of operative exploration, this disease continues to be a focal point for debate.

There are no definitive symptoms that will clearly point to a diagnosis of PLF, however, symptoms may be similar to those of Meniere's disease or endolymphatic hydrops.49-50 Typically, a fluctuating unilateral sensorineural hearing loss occurs. Usually patients complain of associated tinnitus, aural fullness, and vertigo. One or more of these symptoms usually exists. Occasionally, Hennebert's or Tullios sign are seen.54,55 In a symptomatic individual with a clear history of barotrauma, closed head injury or prior otologic surgery, the diagnosis is suspect.

Once the diagnosis of PLF is suspected, there are several tests that can be supportive. Only exploratory tympanotomy with direct observation can confirm the diagnosis and even this can be

subject to error as local anesthetics may seep into the middle

ear space, or minimal trauma on the promontory may cause microvascular disruption with release of vessel exudate. Noninvasive tests, such as the fistula test (positive and negative pressure applied to the tympanic membrane) can produce nystagmus and vertigo. Vertigo is most often seen during the application of negative pressure. Daspit56 coupled ENG testing and the fistula test adding more objective evidence as compared to the standard fistula test.56 Platform posturography testing has been recommended by Black59 with some success in diagnosing and a fistula. Recently Schweitzer60 has identified six "best amino acid markers" which differentiate perilymph from serum, plasma or CSF. These include Theonine, Asparginine, Arginine, Histidine, Valine and Glutamic acid.60

Trauma

Trauma is a frequent cause of vertiginous symptoms. Any insult that disrupts the labyrinth or ossicular chain may lead to vertigo. Transverse temporal bone fractures, typically involve the otic capsule and cause labyrinthine dysfunction. Longitudinal temporal bone fractures less commonly cause vertigo but may do so either from head trauma itself, otic capsule injury or ossicular disruption. A concussive effect on the CNS may result in post-traumatic disequilibrium.

Infection

Acute and chronic infection may affect the middle or inner

ears which may lead to a spectrum of clinical symptomatology. The occurrence of vertigo with acute suppurative otitis media, acute suppurative labyrinthitis and chronic suppurative otitis

media with or without cholesteatoma has been well documented.(ref) Less commonly appreciated is the occurrence of vertigo in childhood related to eustachian tube dysfunction with resultant middle ear effusion. In a study of 27 children with dizziness, Blain62 found that five had serous otitis media or glue ear and, when treated appropriately, their dizziness resolved.

Involvement of the labyrinth secondary to infection may be caused by toxins, by actual bacterial invasion via emissary veins or by semicircular canal erosion.63 There exists a variety of viral causes of inner ear disease including mumps, measles, varicella zoster, cytomegalovirus and influenza B. Delayed onset vertigo may occur because of these viral disorders. For example, mumps causing a severe sensorineural hearing loss in childhood, may not affect the vestibular system until years later, perhaps due to delayed endolymphatic hydrops. While viruses are felt to be important etiologic agents, evidence is mostly circumstantial. At the present time only cytomegalovirus and the mumps virus have been cultured from the perilymph of affected ears.73,74

Autoimmune

Immune-mediated attack upon the inner ear with resultant vertigo, sensorineural hearing loss, aural fullness and tinnitus has been an area of intensive research. It was first highlighted by McCabe in 197964 and elaborated by Hughes.65 Hughes states that autoimmune mediated inner ear disease is diagnosed by clinical findings, positive immunologic laboratory testing and positive treatment response.65 The typical patient is middle aged, female, and exhibits bilateral progressive sensorineural

hearing loss (may be asymmetric) with or without dizziness, aural fullness or tinnitus. Symptoms often progress over weeks to months although sudden hearing loss has been reported.67 Occasionally, the patient may have a systemic immune disease such as rheumatoid arthritis.64,65,66 Hughes65 examined 52 patients suspected of having autoimmune inner ear disease and found 7 to have Cogan's syndrome, 4 with rheumatoid arthritis and 1 having systemic lupus erythematosus.65 Cogan's syndrome is a rare disease characterized by non-syphilitic interstitial keratitis associated with tinnitus, vertigo and hearing loss.68 The etiology is uncertain but evidence suggests that immunologic or infectious causes are likely.69

II.CENTRAL CAUSES OF VERTIGO

Vascular Loop

The idea that vascular compression of cranial nerves may lead to clinically significant symptoms dates back to Dandy's75 first description of trigeminal neuralgia secondary to a vascular loop. It is now well accepted that the cause of tic douloureux and hemifacial spasm is a loop of the anterior inferior cerebellar artery or nearby veins pulsating on the trigeminal or facial nerves respectively.76

More recently, vascular loops compressing the vestibulo- cochlear nerve have been considered a possible cause of hearing loss, vertigo and tinnitus.(ref) The symptoms oftem mimic cerebellopontine angle tumors. Examinations such as pneumo- computed tomography and magnetic resonance imaging (MRI) have, occasionally demonstrated prominent vascular loops penetrating into the internal auditory canal (IAC).77,78 Unilateral delays

observed in auditory brainstem response (ABR) testing has also been correlated with compression of the VIIIth nerve complex by a vascular loop.Moeller16

Anatomic dissections indicate that approximately65% of specimens have vascular loops approaching the VIIth and VIIIth nerves.79,80 McCabe91 described eight patients with discrete spells of true vertigo who were previously diagnosed with Meniere's disease or an unknown cause. All eight patients underwent vestibular nerve section and in each case a vascular loop extending far into the internal auditory canal with compression of the superior vestibular nerve was found. Janetta84 has suggested that patients with vascular loops are more apt to present with constant positional vertigo or disequilibrium with nausea. They generally do not have the typical hearing loss of Meniere's disease and vestibular function testing is many times normal.84

Vertebrobasilar Insufficiency

Vascular insufficiency occurs in the vertebrobasilar system secondary to obstruction, stenosis or "steal" flow patterns. Ischemia is responsible for over 80% of central vestibular disturbances.85 The variable history and clinical findings associated with VBI occur because of the complexity and high numbers of sensory and motor pathways that are supplied by the posterior circulation. Carotid insufficiency secondary to stenosis may cause blood flow reversals in the posterior communicating artery with a resultant "steal phenomenon" from the vertebrobasilar system.85

Grad examined a series of 84 patients with posterior circulation problems and found that there was a high incidence of isolated episodes of vertigo associated with vertebrobasilar insufficiency. He also described a 42% incidence of unilateral caloric weakness, concluding that the vestibular labyrinth is selectively vulnerable to ischemia from disorders in the vertebrobasilar system.86 Visual dysfunction, drop attacks, unsteadiness and extremity weakness were the most common associated symptoms in patients with VBI.86

In Valvossori's85 study of 200 patients with VBI, 87% complained of dizziness. He suggested that if computed tomographic dynamic exams were suspicious of flow aberrations, angiography should be obtained to confirm the flow abnormality.85

Multiple Sclerosis

Multiple sclerosis is a demyelinating disorder that is characterized by a variety of neurological signs and symptoms

which have a tendency towards remission and exacerbation. Typically, MS is a disease of young adult white females.

The etiology is unknown, however, based upon epidemiologic and virologic studies, it is suggested that MS may be caused by an abnormal immunologic response to prior viral exposure.89 Recent studies show wide discrepancies in the percentage of symptoms of vertigo or disequilibrium, ranging from 5% to 51%.92,93 A gaze induced horizontal nystagmus is thought to occur in up to 70% of patients with MS. Vertical nystagmus occurs in approximately one third of multiple sclerosis patients.(need reference)

Migraine

Migraine was fist described by Hippocrates 25 centuries ago.96 It is a common disorder that affects approximately 25% of women, 20% of men and 2-5% of children.94,95 Typically, migraine is characterized by periodic headaches that are occasionally associated with nausea, vomiting and neurologic symptoms. In common migraine, absence of neurologic symptoms is the rule whereas in classical migraine an aura typically precedes the headaches.94,97,98 It is also well documented that neurologic symptoms termed "migraine equivalent" can occur in the interval between headaches.99 Of 200 patients with migraine examined by Kayan and Hood,100 53 complained of vertigo. Vertigo was noted as an aura in 8 patients, during the headache in 25 patients, after the headache in 1 patient, and between headaches in 19 patients.100

Bickerstaff was the first to describe basilar artery migraine. This was characterized by an aura of scotomata, transient blindness, vertigo, dysarthria, parasthesias, ataxia and tinnitus.

Cervical Vertigo

Cervical vertigo was first documented by Claude Bernard in 1858.107 Longet and Shift108,109 described gait disorders resembling cerebellar ataxia after severing cervical muscles in several animal species.108,109 There are several theories as to he etiology of cervical vertigo including inflammatory and degenerative changes in the cervical spine or neck musculature which can lead to altered neck proprioceptive input. These reflexes or impulses are important for cervical righting reflexes. Barre110 injected 1% procaine into deep cervical tissues and found not only vertigo, horizontal contralateral nystagmus, ipsilateral past pointing, and falling toward the injected side, but also observed tinnitus and an ipsilateral Horner's Syndrome.110 Vascular insufficiency may be another cause of cervical vertigo. It is well known that turning the head leads to decrease flow in vertebral vessels,111 however, general cardiovascular causes such as atherosclerosis appear more important. Irritation of the cervical sympathetic system has also been implicated as a potential cause of cervical vertigo.110.112

III.MISCELLANEOUS CAUSES OF VERTIGO

There are multiple metabolic derangements that have been implicated as causative factors in inner ear disease

According to Rubin117 there are five major organ systems responsible for inner ear homeostasis. These include the adrenal and pituitary glands, the hormonal and immune systems and the hypothalamus.117

The most frequent laboratory abnormality associated with vestibular dysfunction in hyperglycemia. Frequently dietary manipulation will lead to a beneficial response.118,119 Spencer120 reported on 1,400 patients with hearing loss and vertigo who were diagnosed with hyperlipidemia. Hypothyroidism has also been implied as a potential cause of neuro-otologic dysfunction.118

Many different drugs are known to produce vertigo including alcohol, Phenobarbital, Dilantin, Chlorpromazine, Adrenocorticotropic antagonists, Cholinomimetics, Cholinesterase inhibitors and Gammaaminobutyric acid agonists.121

It has also been suggested that food allergies or inhalant allergies may be a contributing factor in the development of endolymphatic hydrops. Shambaugh currently encourages dietary management of food allergens for relief of symptoms of Meniere's Disease.122

MEDICAL TREATMENT OF VERTIGO

Meniere's Disease

Treatment options for Meniere's disease are diverse. Initial medical treatment includes a salt restricted diet often in combination with a diuretic. Other dietary adjustments proposed by Spencer and Kinney are a reduction of carbohydrate and lipid intake.25,26

The oral diuretics (Benthiazides, Chlorthalidone, potassium- sparing drugs and Furosemide) are commonly used. It is interesting to note that this type of therapy tends to reduce the number and severity of the vertiginous attacks, but it has not been shown to have a long term effect on hearing.13-15 In contrast, osmotic diuretics have shown dramatic, albeit temporary, improvement in hearing in approximately 60% of patients with Meniere's disease.16-18 Examples of osmotic diuretics include glycerin, Mannitol, urea and isosorbide. The effect of these drugs is to withdraw water from the labyrinth.

Vasodilator therapy has been used with some success. Overall, it is felt to be effective in acute situations, stabilizing hearing and reducing vertigo. Vasodilatory agents currently in use are Nicotinic acid,20 intravenous Histamine20 and Betahistidine21 (an oral histamine preparation). Carbon dioxide with oxygen (carbogen), a potent vasodilator, has been reported to improve hearing.(Fisch ref) Hearing improvement is more likely to be seen in early stages of Meniere's.19-21

Pressure chamber therapy has been touted to be successful

in providing long lasting improvement in both hearing and vertigo in 45% of Meniere's patients. The decompression chamber causes a reduction in air pressure which creates a relative positive pressure in the middle ear decreasing venous congestion and reducing endolymphatic hydrops.20

McCabe23 has demonstrated that vestibular suppressants, specifically Diazepam, are effective in reducing the

vestibular symptoms associated with Meniere's disease. Daily therapy is considered important in reducing the likelihood of recurrent vertigo. Anticholinergics are also helpful in ameliorating associated nausea and vomiting.

Graham was able to demonstrate preservation of or improvement in hearing as well as alleviation of vertiginous episodes in patients with bilateral intractable Meniere's disease using titration Streptomycin therapy. The purpose of this treatment is to eliminate vertigo short of creating oscillopsia or hearing loss. This is achieved by frequent assessment of audiologic and vestibular function during treatment.

Vestibular Neuronitis

Treatment for vestibular neuronitis is essentially symptomatic. During the acute phase it is important to provide the patient relief from the intense vertigo, nausea and vomiting. This includes the use of a vestibular suppressant such as Diazepam or Meclazine combined with an antiemetic. Short term steroid use has also been effective.(Reference) It is important to limit the use of vestibular suppressants to the acute stage of the disease, thereby allowing compensation to occur in the long term.

Benign Positional Vertigo

Treatment for BPV is primarily symptomatic. During acute exacerbations vestibular suppressants such as Benzodiazepines and antihistamines are used. However, in order to habituate the vestibular system rather than suppress it, head exercises or customized vestibular exercises(ref) are used which reduce symptomatology and lessening the severity of recurrences.

Perilymphatic Fistula

The mainstay in medical management of PLF is bedrest for seven to ten days.(Reference needed) Vestibular suppressants may be effective in alleviating vertigo in the early stages of this disease. Failure of bedrest to resolve the vertigo or a progression of the sensorineural hearing loss are indications for surgical intervention.

Autoimmune Inner Ear Disease

Glucocorticoids have been the primary treatment for autoimmune inner ear disease and Cogan's syndrome.(McCabe) & 70,71 Cyclophosphamide and Azathioprine have also been used with some success.70 Plasmapheresis has lead to good results as documented by Luetje.88 Plasmapheresis entails the removal of plasma from withdrawn blood thereby removing antibodies, antigens, immune complexes and blocking antibody.88 Leutje studied eight patients diagnosed with autoimmune inner ear disease and concluded that plasmapheresis can be used as alternative or adjunctive therapy in patients with autoimmune inner ear disease in that it stabilizes or improves auditory and vestibular symptoms in selected patients.88

Migraine

Medical intervention for vertigo associated with migraine includes the typical treatments for migraine headaches.

During an attack, Ergotamine tartrate helps alleviate symptoms.101 Propranolol has been effectively used in long-

term control of migraine symptoms including vertigo102-104 as have calcium channel blockers Amitriptyline, Periacton and Methysergide Maleate.101,105,106

SURGICAL TREATMENT OF VERTIGO

Surgical therapy for vertigo is considered when conservative management (diet and medical) fails. Prior to surgery, the pathology needs to be isolated to the peripheral vestibular system and the diseased ear needs to be identified through history and auditory - vestibular testing. Various other factors such as hearing level, severity and frequency of symptoms and physiological age must also be considered. Two types of surgical procedures exist which offer relief of vertigo: preservation procedures (endolymphatic sac surgery,

cochleosacculotomy, microvascular decompression and perilymphatic fistula repair) and ablative procedures (labyrinthectomy, vestibular nerve section, singular neurectomy, posterior semi- circular canal occlusion and streptomycin perfusion of the labyrinth).

Endolymphatic Sac Surgery

Several surgical procedures have been proposed to treat vertigo associated with Meniere's disease 1,2,3,4 and delayed onset of vertigo (delayed endolymphatic hydrops).5,6 In those patients refractory to medical management, endolymphatic sac surgery can be offered as an attempt to decompress the hydropic condition (increased endolymphatic fluid) which is thought to exist in the diseased ear.

Various techniques of decompression include endolymphatic sac-subarachnoid shunts,4 endolymphatic sac-mastoid shunts,6 and wide bony decompression of the endolymphatic sac.1,2 Despite the technique used the success rate for endolymphatic sac surgery has ranged from 60-85%1,2,3,4,5,6,7,8 with respect to a reduction in or a cure of vertigo. Hearing improvement occurs in 10-56%.6,7,8 Aural pressure is often reduced and occasionally tinnitus is lessened.

The above results are comparable to those of Bretlau et al.7 who evaluated 23 patients with active Meniere's disease. In their double blind study approximately 70% of patients receiving either a simple mastoidectomy or endolymphatic-mastoid shunt experienced an elimination of or a significant reduction in their vertigo. These results were reported after a nine year followup period. The author argued for a strong placebo effect of sac surgery and suggested that the effect of surgery was not specifically related to manipulation of the sac.

Several authors offer endolymphatic sac decompression- shunting as an early alternative in Meniere's patients hoping to reduce or eliminate vertigo and stabilize hearing. Brown9 reviewed 245 patients who underwent endolymphatic sac surgery and found that in the early stages of Meniere's disease 75% of patients had relief of vertigo while 50% had continued relief after 10 years. If surgery was offered in the late stages of the disease, only 40% demonstrated improvement. The majority of the latter group had a progressive decline in their hearing.

The surgical technique is straightforward. After performing a wide mastoidectomy, bone is removed from over the endolymphatic sac located in the posterior fossa dura just inferior to a line (Donaldson's line) drawn through the posterior semicircular canal where it is bisected by the horizontal semi- circular canal (figure 1). At this point the surgeon has the option of opening the sac and placing a drain or valve in it.

A recent modification of this technique introduced by Kartush,10 involves bony decompression not only of the posterior fossa dura and endolymphatic sac but also wide decompression of the sigmoid sinus. In conjunction, the sigmoid sinus size is reduced with the aid of bipolar cautery. Initial results have been promising with 90% of patients demonstrating complete to substantial control of vertigo at one year.

Complications resulting from endolymphatic sac surgery are rare and occur in less than 2% of cases.1 The risk of a sensori- neural hearing loss is slightly increased when the sac is opened and a valve or shunt is placed.

Revision sac surgery has been shown to be equally as effective as a primary endolymphatic sac procedure if symptoms recur.11 Paparella12 has shown that, along with vertigo reduction, hearing gain can occur following a revision endolymphatic sac procedure.

Cochleosacculotomy

Schuknecht, in 198213 introduced the concept of creating a fistula between the endolymphatic and perilymphatic spaces there by decompressing the endolymphatic compartment . The

cochleosacculotomy procedure involves inserting a 4mm hook

through the round window membrane and the osseous spiral lamina of the basal turn of the cochlea. The round window is then sealed. This procedure can be performed transcanal, under local anesthesia.

The procedure is primarily indicated for Meniere's disease. Since the surgery can be performed under local anesthesia, it can be done in the elderly and those who are poor surgical risks. Schuknecht14 reports up to 72.6% of patients obtained relief of vertigo and 55% maintained hearing. Although considered a preservation procedure, it should not be performed in an only hearing ear as up to 45% of patients develop a severe to profound sensorineural hearing loss (11/90) in the operated ear.

Microvascular Decompression of the VIIIth Nerve Complex

Microvascular decompression of the VIIIth nerve complex has been introduced by Janetta and Moller15 as a method to relieve disabling positional vertigo (DPV). Patients with DPV present with a constant sensation of being off balance that is associated with nausea. The diagnosis is usually made by history and abnormal auditory brainstem evoked response testing (ABR). A difference of 0.2 msec in the latency of peaks I-III compared to the contralateral side or an absolute increase in the I-III latency exceeding 2.3 msec is considered an indication of VIIIth nerve compression.

Following a retrosigmoid craniectomy, the VIIIth nerve complex is identified as it leaves the brainstem and enters the internal auditory canal. Vascular compression is reduced by inserting a small piece of teflon felt between the nerve and a blood vessel which lies on the nerve.

Moeller16 reported the results of 41 patients undergoing microvascular decompression for DPV. Thirty patients became totally symptom free or had a marked improvement in symptoms. Two patients had a mild improvement in their symptoms and nine experienced no relief. The author states that all patients had a significant compression of the VIIIth nerve by one or more vessels. One patient suffered a complete loss of hearing due to the microvascular decompression procedure. Moeller16 concludes that microvascular decompression is an effective method of treating disabling positional vertigo with gradual improvement of symptoms noted 4-12 months postoperatively.

Perilymphatic Fistula Repair

A leak of perilymphatic fluid from either the round or oval windows, generally associated with an episode of barotrauma, can cause a variety of ear symptoms including sensorineural hearing loss and vertigo. Seltzer and McCabe18 note that disequilibrium, with occasional spells of true vertigo, is the most common vestibular symptom pattern.

The technique of perilymphatic fistula repair involves an exploratory tympanotomy under local anesthesia. The oval and round windows are then observed.

Patients are placed in the head down position and are asked to bear down while the surgeon examines each window. Fascia, perichondrium or fat supported by gelfoam is then used to seal each window.

Shelton and Simmons17 report that in patients in whom a perilymphatic fistula was observed, 64% had resolution of their major symptom. When no fistula was found, 44% demonstrated resolution of their major symptoms. Seltzer and McCabe18 found that closure of a perilymphatic fistula improved vestibular symptoms in the majority of cases however auditory symptoms improved to a lesser degree.

The most difficult aspect of a perilymphatic fistula repair is the recognition of a true leak of perilymphatic fluid. To this end investigators are pursuing tests which would specifically identify perilymphatic fluid as compared to other body fluids or local anesthetics.

Labyrinthectomy

A labyrinthectomy is an ablative procedure in which the sensory epithelium and distal nerve fibers are removed from the vestibular end organ. It is generally performed in patients with non-serviceable hearing, (greater than 60 dB speech reception threshold and speech discrimination less than 50%) and symptoms of vertigo or disequilibrium. In a majority of cases, electronystagmography reveals hypofunction of the involved ear (that with a marked sensorineural hearing loss) although the vestibular response in the diseased ear may be normal or totally absent.

A labyrinthectomy can be performed by one of two approaches; transcanal or transmastoid. The transcanal labyrinthectomy, first described by Schuknecht in 1956,19 involves removing the stapes and curettage of the vestibule. Armstrong20 in 1959 advocated removal of a portion of the promontory to allow for more complete removal of neural epithelium. Vertigo is controlled in over 90% of patients with a properly performed labyrinthectomy.

To allow for more complete removal of neural epithelium and distal nerve fibers, Pulec21 described the transmastoid labyrinthectomy procedure in 1969. This technique involves a mastoidectomy with fenestration of the horizontal, posterior and superior semicircular canals as well as the vestibule.(figure 2) Under direct vision, the ampullae of the three semicircular canals and maculae of the saccule and utricle can be completely removed.

Graham and Kemink22 discussed their five year experience with this technique and noted a 93% success rate in controlling vertigo. As expected, all residual hearing is lost with this procedure. The complication rate following labyrinthectomy is low. There is a 2% incidence of facial weakness.

Vestibular Nerve Section

Vestibular nerve section has become the most accepted method of controlling medically refractive vertigo or disequilibrium caused by unilateral vestibular dysfunction in patients with serviceable hearing. In several studies23,24,25, regardless of the surgical approach, those patients with Meniere's disease faired better with respect to alleviation of vertigo than did non-Meniere's patients.

There are currently four surgical approaches commonly used to perform a vestibular nerve section; middle cranial fossa, retrolabyrinthine, retrosigmoid and translabyrinthine. All but the latter offer the opportunity for hearing preservation. Until 1961, vestibular nerve section was performed by the suboccipital route. In 1961 House26 introduced the middle cranial fossa approach (figure 3). This involves a temporal craniectomy with retraction of the temporal lobe medially exposing the superior surface of the temporal bone. After opening the internal auditory canal the superior and inferior vestibular nerves are individually sectioned. Utilizing this approach, relief of vertigo was obtained in 85-99% of patients27,28. The advantage of the middle cranial fossa approach over other surgical approaches used for vestibular nerve section in the ability to completely section all vestibular fibers prior to their becoming more intimately associated with cochlear fibers as has been demonstrated in the cerebellopontine angle. The disadvantages of the middle cranial fossa technique stem from a greater risk of facial nerve injury and sensorineural hearing loss. The risk of neurological complications (aphasia, seizures and hemiparesis) may be higher with this approach.

In 1980 Silverstein and Norrell29 introduced the retrolabyrinthine vestibular neurectomy. This allows direct access to the cerebellopontine angle (CPA). After a wide mastoidectomy is performed, bone is removed from over the sigmoid sinus and posterior fossa dura down to the posterior semicircular canal. The dura is incised just inferior to the superior petrosal sinus, gaining exposure to the CPA. The VIIIth nerve complex is identified and the vestibular portion of the nerve, located on the tentorial side, is sectioned. Approximately 75% of nerves demonstrate a distinct cleavage plane between the cochlear and vestibular division.30

Results are excellent with this approach. Silverstein,27 reports a 93% success rate in resolving or improving vertigo with no patients demonstrating a total neural hearing loss. The risk of facial nerve weakness compared to middle cranial fossa approach, was significantly reduced from 4% to 0%.31 Drawbacks to the retrolabyrinthine approach include a 3-10% incidence of cerebrospinal fluid leakage, limited exposure of the neurovascular structures in the cerebellopontine angle, the risk

of facial nerve or posterior semicircular canal fenestration within the mastoid and increased risk of limited exposure if the sigmoid sinus is anterior, the jugular bulb is high or the mastoid is sclerotic.31

Due to limitations of the retrolabyrinthine approach several authors have advocated the retrosigmoid technique,25,30 for sectioning the vestibular nerve. This procedure involves exposing the sigmoid and lateral sinuses and performing a craniectomy posterior and inferior to these structures (figure 4). The dura is cut in a linear curve manner exposing the cerebellum (figure 5). Minimal retraction on the cerebellum results in wide exposure of the cerebellopontine angle (figure 7). The vestibular nerve is then sectioned.(figure 7) The dura is closed tightly, markedly reducing the incidence of a cerebrospinal fluid leak.31,32

Control of vertigo, obtained after performing a retro- sigmoid vestibular nerve section is similar to that obtained with the retrolabyrinthine approach (93-95%)25. Disadvantages of the procedure involve the close association of cochlear and vestibular fibers in the cerebellopontine angle as well as headaches. Headaches have nearly been eliminated with the use of two modifications introduced by Kartush32. Bicol, a soft non- adherent collagenous material is placed between the retractors and the cerebellum to minimize trauma and the bone plug, obtained from the craniectomy site, is replaced after the dura is closed.

The translabyrinthine approach for sectioning the vestibular nerve involves performing a labyrinthectomy, exposing the internal auditory canal with subsequent sectioning of the superior and inferior vestibular nerves.33 This procedure, as opposed to the other approaches for performing a vestibular neurectomy, involves total loss of hearing. In our experience, a complete transmastoid labyrinthectomy obviates the need for a translabyrinthine vestibular nerve section. Failure of the transmastoid labyrinthectomy to control vertigo either results from an incomplete procedure (retained neural epithelium) or concurrent disease in the contralateral labyrinth or central nervous system.

Singular Neurectomy and Posterior Semicircular Canal Occlusion

Benign positional vertigo (BPV) is generally a self-limited disorder associated with pathology involving the posterior semi- circular canal ampullae.34 Patients with BPV are generally free of their vertiginous symptoms within one year of their onset. Those with symptoms past 12 months appear to have intractable disease.

Two procedures have been advocated for the relief of symptoms of benign positional vertigo; singular neurectomy and occlusion of the posterior semi-circular canal. Gacek35 introduced the singular neurectomy approach in 1974. It involves lifting a tympanomeatal flap by a transcanal approach. After identifying the round window membrane, the singular canal is found by drilling 1-2 mm deep to the inferior round window membrane in the posterior one third of the round window nitch. The nerve to the posterior ampullae is then avulsed with a hook.

Relief of vertigo occurs in 91-97% of patients36,37 following this procedure. Drawbacks to this procedure include a 6-8% incidence of sensorineural hearing loss in the most experienced hands.36 The difficulty in adequately exposing the posterior ampullated nerve has lead many otologic surgeons into performing a complete vestibular neurectomy for persistent benign positional vertigo.

Parnes and McClure38 have recently introduced a transmastoid posterior semi-circular canal occlusion procedure, effectively relieving intractable benign positional vertigo in two patients. Each patient demonstrated preserved lateral semi-circular canal function. Both patients had a preoperative profound sensorineural hearing loss. The authors are currently examining the effect of this procedure in patients with serviceable hearing. After a mastoidectomy is completed, a small diamond burr is utilized to penetrate the posterior semi- circular canal impacting bone ships within the adjacent canal ends. A layer of fascia sealed with human fibrinogen glue is then placed on each canal end to secure occlusion.

Streptomycin Profusion of the Labyrinth

A new surgical procedure introduced by Norris and Shea 199039 involves fenestration of the horizontal semicircular canal creating a fistula between endolymph and perilymph and applying Streptomycin (125 micrograms) between the bony canal and membranous duct. Fifteen patients with Meniere's disease were treated in the initial study. According to the author, all 15

enjoyed complete remission of their vertigo and 7 of 8 patients treated with a dose of 125 micrograms maintained their hearing. Although preliminary results are encouraging, further clinical trials will be needed to assess both short and long term vertigo control rates as well as hearing stability.

Conclusion

Several medical approaches and surgical procedures are available for control of vertigo. Essential to their use are a fundamental knowledge of the anatomy and physiology of the vestibular system and an understanding of the strengths and weaknesses of vestibular testing. With the development of newer modalities for vertigo control, prospective randomized studies will be needed to assess the value of both new and old treatments which may relieve vertigo.

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