Transcanal Labyrinthectomy

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 the 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. However, experience with transcanal labyrinthectomy, such as vestibular neurectomy, has dramatically decreased in recent decades, likely due to the efficacy of intratympanic gentamicin injection and the consequent reduction in the number of labyrinthectomies being performed.

Medical management appropriate to the unilateral vestibular disorder, including vestibular suppressants and diuretics for Ménière disease, and intratympanic gentamicin or steroids (see Chapter 36 ) should be attempted before considering 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 Ménière disease of 10% to 40%, as reported by Greven and Oosterveld and Paparella and Griebie, 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 poorer and a speech discrimination score of less than or equal to 20%. This threshold for labyrinthectomy should be increased if the 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 only be done for debilitating peripheral vestibular dysfunction. That is, a patient with only mild or infrequent attacks may be best treated without surgery. 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 the total ablation of peripheral vestibular dysfunction but also on compensation for this unilateral vestibular loss. The 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 the Hennebert signs should be done. A neurological examination should be done to exclude concurrent cranial nerve, cerebellar, or other neurological dysfunctions 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. However, the symptoms and findings of long-standing unilateral Ménière disease may be similar to the symptoms and findings caused by lesions of the posterior fossa. MRI with gadolinium enhancement is useful to exclude 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 neurological and radiographic evidence of central neurological disease.

Generally, the functional outcome is better in patients with unilateral Ménière disease than in those with other peripheral vestibular dysfunction. In some patients with Ménière 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 Ménière disease is sufficient to warrant labyrinthectomy, even in the presence of normal caloric function if the other selection criteria are met. The patient should be aware that postoperative vertigo is more severe when the 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 Ménière 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. 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 after surgery there is a period of vertigo similar to a typical attack, and that this episode lasts several days. In addition, a period of protracted disequilibrium may occur, and in patients with negative indicators for compensation, there may be some degree of permanent disability that requires a rehabilitative program.

The alternative treatments for the vestibular symptoms of Ménière disease should be well understood by the patient. The discussion thereof should include the medical regimens; alternative ablative techniques, including intratympanic gentamicin injection (see Chapter 36 ), and transmastoid or translabyrinthine approaches for labyrinthectomy; and selective ablative techniques through the middle or posterior fossa to save the residual hearing. 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 a fat graft may be necessary.

Surgical Technique

General anesthesia is required because of the violent vestibular response during the removal of the vestibular end-organs. One exception may be in a revision labyrinthectomy in an ear with minimal residual vestibular function. In such cases, local anesthesia may allow intraoperative confirmation that the site of the residual vestibular function has been located. The patient is placed supine in a head holder with the head positioned similar to any transcanal procedure. The hair is shaved 0.5 inches (1.3 cm) around the auricle and prepared with an antiseptic solution. Generally, systemic antibiotics and steroids are not required.

Facial nerve monitoring is usually not performed in primary labyrinthectomy, but may be useful in a revision procedure if there is considerable scarring in the oval window area. No special instruments are necessary, but an instrument to remove the utricle from the recesses of the vestibule and a probe to destroy the cristae of the three semicircular canals mechanically should be available. For these purposes, a 4-mm right-angled hook or a whirlybird is useful. A microdrill is necessary to widen the oval window or to connect the oval and round windows for exposure.

Incision and Exposure

The procedure is done by the transcanal approach in most cases. Occasionally, with a very narrow meatus, an endaural incision or postauricular transcanal approach may be useful. An anteriorly-based tympanomeatal flap, longer than that used for stapedectomy, is elevated to allow wide curettage in the oval and round window areas ( Fig. 35.1 ). The horizontal segment of the facial nerve, entire stapes footplate, and entire round window niche all should be easily visible after elevation of the flap and curettage of the posterior aspect of the bony tympanic annulus.

Preparation for Opening the Vestibule

The incus is removed. The stapedial tendon is sectioned and the stapes removed in a rocking motion in an anteroposterior direction to allow the removal of the stapes without fracture. Every effort should be made to avoid aspiration of the vestibule at this time to avoid displacement of the utricle. To obtain access to the vestibular end-organs, the oval window may simply be enlarged at its anterior and inferior aspects ( Fig. 35.2 ), or the oval and round windows may be connected to remove a segment of the promontory ( Fig. 35.3 ). At this juncture, an attempt may be made to expose the posterior ampullary nerve. It may be exposed near the posterior aspect of the round window niche (see Figs. 35.2 and 35.3 ), which affords the surgeon an opportunity to practice the identification and section of the posterior ampullary nerve, and helps guarantee a more complete labyrinthectomy. In a study of labyrinthectomy in the cat, Schuknecht reported that the subtotal destruction of the vestibular end-organs occurred in 10 of 24 ears, and that the crista of the posterior semicircular canal was the end-organ most commonly missed.