Transcanal Labyrinthectomy

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Chapter 40 Transcanal Labyrinthectomy

Joseph B. Nadol, Jr., Michael J. McKenna

Labyrinthectomy is an effective surgical procedure for the management of unremitting or poorly compensated unilateral peripheral vestibular dysfunction in the presence of ipsilateral, profound, or severe sensorineural hearing loss. The physiologic rationale is that central vestibular compensation is more rapid and complete for unilateral absence of peripheral vestibular function than for unilateral abnormal function, either episodic or chronic.¹

Unilateral vestibular ablation has been advocated for more than 6 decades. Selective or total eighth cranial nerve transection by the suboccipital approach was introduced by Dandy in 1928.² Destruction of the peripheral end organs of the vestibular labyrinth was introduced by Jansen³ in 1895 for complications of suppurative labyrinthitis. This technique was applied to unilateral peripheral vestibular disturbance by Milligan⁴ and by Lake⁵ in 1904, and was reintroduced by Cawthorne⁶ in 1943 as a canal wall up technique. In his original description, Cawthorne apparently ablated only the lateral semicircular canal. In its current form, complete vestibular ablation is accomplished by exenteration of all three of the semicircular canals and both maculae.

The earliest report of a transcanal procedure for vertigo is credited to Crockett,⁷ who in 1903 described removal of the stapes as an effective treatment for vertigo. Lempert⁸ described an endaural transmeatal approach to the oval and round windows for Meniere’s disease. In this procedure, the stapes was removed, and the round window was punctured to “decompress” the membranous labyrinth. There was no mention, however, of the importance of destruction of the vestibular end organs. The modern transcanal labyrinthectomy for unilateral peripheral vestibular dysfunction was introduced by Schuknecht in 1956⁹ and by Cawthorne in 1957.¹⁰ In a series of articles, Schuknecht’s technique evolved to emphasize the importance of destruction of all five vestibular end organs.¹¹^–¹³ Armstrong¹⁴ and Ariagno¹⁵ also emphasized the importance of total ablation of peripheral vestibular function.

PATIENT SELECTION

The modern complete transcanal labyrinthectomy is an extremely effective treatment option for unilateral peripheral vestibular dysfunction. Rates of control of vertigo of 95% to 99% have been achieved by several authors. The modified Cawthorne transmastoid labyrinthectomy and the translabyrinthine vestibular or eighth cranial nerve section are equally effective options for ablation of peripheral vestibular dysfunction. The transcanal labyrinthectomy has the advantages of a more direct approach to the vestibular end organs, a shorter operating time, and a lower morbidity, particularly for postoperative facial nerve dysfunction and cerebrospinal fluid leak.

Medical management appropriate to the unilateral vestibular disorder, including vestibular suppressants and diuretics for Meniere’s disease, should be attempted before consideration of labyrinthectomy. These forms of medical management are less successful for poorly compensated peripheral vestibular dysfunction, such as the sequelae of vestibular neuronitis, labyrinthitis, or trauma. In these cases, rehabilitative vestibular physical therapy should be attempted before labyrinthectomy. Labyrinthectomy should be performed only when it has been shown that the vestibular dysfunction is unilateral, and when the ipsilateral hearing loss is severe or profound.

Although the published indications for labyrinthectomy have included hearing levels poorer than a 50 dB speech reception threshold and a 50% discrimination score, in view of the incidence of bilateral Meniere’s disease of 10% to 40%, as reported by Greven and Oosterveld ¹⁶ and Paparella and Griebie,¹⁷ labyrinthectomy should be reserved for cases in which the hearing loss is severe to profound, generally with a speech reception threshold of 75 dB or worse and a speech discrimination score of less than or equal to 20%. This threshold for labyrinthectomy should be increased if hearing in the contralateral ear is not in the normal or near-normal range.

Because of the acute and often protracted vestibular disturbance after labyrinthectomy, this procedure should be done only for debilitating peripheral vestibular dysfunction. That is, a patient with only mild or infrequent attacks may be best treated nonoperatively. The definition of handicapping vertigo also depends on many other clinical factors, such as age, intercurrent disease, and occupation of the patient.

A successful labyrinthectomy depends not only on total ablation of peripheral vestibular dysfunction, but also on compensation for this unilateral vestibular loss. Negative indicators for successful vestibular compensation generally include increased age, visual disturbances, obesity, sedentary lifestyle, arthritis or other lower limb dysfunction, dependent personality, or clear indication of secondary gain.

PREOPERATIVE EVALUATION

A complete history and otolaryngologic–head and neck examination should be performed. Bilateral behavioral audiometry, including pure tone thresholds for air and bone conduction and speech discrimination, is necessary. Vestibular testing should include at least bilateral caloric function, best done by electronystagmography. This assessment is necessary to evaluate the possibility of bilateral vestibular dysfunction, and to confirm vestibular dysfunction in the affected ear based on audiometry and history. Hallpike’s positional testing and evaluation for the presence of the fistula and Hennebert’s signs should be done.¹⁸ A neurologic examination should be done to rule out concurrent cranial nerve, cerebellar, or other neurologic dysfunction that would belie the working diagnosis of a peripheral unilateral vestibular dysfunction.

Radiographic assessment with computed tomography (CT) and magnetic resonance imaging (MRI) is not essential in every case. The symptoms and findings of long-standing unilateral Meniere’s disease may be similar, however, to the symptoms and findings caused by lesions of the posterior fossa. MRI with gadolinium enhancement is useful to rule out cerebellopontine angle or other tumors and demyelinating lesions. The ideal candidate for labyrinthectomy is an individual with unremitting or uncompensated peripheral vestibular dysfunction with severe to profound unilateral sensorineural hearing loss, unilateral vestibular dysfunction on electronystagmography, and lack of neurologic and radiographic evidence of central neurologic disease.

Generally, the functional outcome is better in patients with unilateral Meniere’s disease than in patients with other peripheral vestibular dysfunction. In some patients with Meniere’s disease, electronystagmography is normal. In such cases, labyrinthectomy is justified if the symptoms and signs are sufficiently localizing to be convincing of unilateral peripheral dysfunction. The presence of fluctuating or severe to profound sensorineural loss, ipsilateral tinnitus, and aural symptoms concurrent with an attack of Meniere’s disease is sufficient to warrant labyrinthectomy, even in the presence of normal caloric function if other selection criteria are met. The patient should be aware that postoperative vertigo is more severe when preoperative function is normal or nearly so in the affected ear.

PREOPERATIVE PATIENT COUNSELING AND INFORMED CONSENT

Preoperative counseling should include a discussion of the natural history of Meniere’s disease, including the spontaneous rate of remission of approximately 70% within 8 years and the 10% to 40% incidence of involvement of the second ear.¹⁹ In addition, the patient should be aware that all hearing will be lost in the ear receiving surgery, and that the effect on tinnitus is unpredictable. The patient must be aware that immediately postoperatively there is a period of vertigo similar to a typical attack, and that this episode lasts several days. In addition, a period of protracted dysequilibrium may occur, and in patients with negative indicators for compensation, there may be some degree of permanent disability that requires a rehabilitative program.

A discussion of alternative treatments for the vestibular symptoms of Meniere’s disease should be well understood by the patient. The discussion should include medical regimens; alternative ablative techniques, including transmastoid or translabyrinthine approaches; and selective ablative techniques through the middle or posterior fossa to save residual hearing. Particularly in elderly patients or in patients with other negative indicators for compensation, a round window labyrinthotomy should be considered and discussed with the patient as a possible alternative to labyrinthectomy. This procedure has the advantage of not resulting in a protracted period of dysequilibrium, and does not preclude a labyrinthectomy, if necessary. The usual risks of ear surgery also should be discussed, including paresis or paralysis of the facial nerve, perforation of the tympanic membrane, dysgeusia, failure of the procedure to achieve the desired result, the possible need for revision or secondary procedures, cerebrospinal fluid leakage or meningitis, and the fact that harvesting of a fat graft may be necessary.