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 Oosterveld¹⁶ 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.

SURGICAL TECHNIQUE

General anesthesia is required because of the violent vestibular response during 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 residual vestibular function has been located. The patient is placed in a supine position in a head holder with the head positioned similar to any transcanal procedure. Hair is shaved 0.5 inch around the auricle and prepared with an antiseptic solution. Generally, systemic antibiotics and steroids are not required.

Facial nerve monitoring is usually not done in primary labyrinthectomy, but may be useful in a revision case 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 mechanically the cristae of the three semicircular canals should be available. For these purposes, a 4 mm right angled hook or a whirlybird from the Austin middle ear instrument set 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. 40-1). The horizontal segment of the facial nerve, the entire stapes footplate, and the 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.

FIGURE 40-1 Incisions for transcanal labyrinthectomy. Anteriorly based tympanomeatal flap should be slightly wider and longer than flap used for stapedectomy to allow wide curettage of bony tympanic annulus. Curettage should allow visualization of horizontal segment of the facial nerve and entire oval and round window niches.

FIGURE 40-2. Access to vestibule may be achieved by widening oval window niche by removing a segment of promontory. At this time, posterior ampullary nerve may be located in the floor of the round window niche. This step is facilitated by removal of round window overhang.

FIGURE 40-3. As an alternative method to expose vestibule, the round and oval windows may be connected to remove lateral aspect of the promontory.

FIGURE 40-4. Normal anatomic positions of five vestibular end organs are superimposed on surgical exposure.

Removal of Vestibular End Organs

Total mechanical destruction of the five vestibular end organs is the goal of this surgery. The normal position of the vestibular end organs and their relationship to the oval and round windows are shown in Figure 40-4. Endolymphatic hydrops or intraoperative loss of perilymph may cause displacement of these end organs, however. During aspiration or loss of perilymphatic fluid, the utricle usually retracts superiorly to lie medial to the horizontal segment of the facial nerve. Before aspiration of the vestibule, the utricle should be removed with a 4 mm hook, whirlybird, or utricular hook in the superior aspect of the vestibule (Fig. 40-5).

FIGURE 40-5 Removal of utricle can be accomplished with a 4 mm hook (as shown), utricular hook, or whirlybird. Removal of utricle often results in simultaneous avulsion of ampullary ends of the lateral and superior canals, but not of the posterior canal.

FIGURE 40-6. After removal of utricle and aspiration of saccule, any residual neuroepithelium of the three semicircular canals is destroyed by mechanical disruption using a 3 to 4 mm angled hook.

FIGURE 40-7. After avulsion and destruction of vestibular end organs, vestibule is filled with Gelfoam soaked in gentamicin or streptomycin solution and a tissue graft, such as fat.

The utricle is substantial and can easily be seen under low power of the operating microscope. Avulsion of the utricle from the vestibule usually results in avulsion of the cristae of lateral and superior semicircular canals as well, but not that of the posterior semicircular canal. The saccule is destroyed mechanically by aspiration of the medial aspect of the vestibule in the area of the spherical recess. Manipulation of the medial aspect of the vestibule must be done with care to avoid fracture of the cribrose area, which would result in profuse leakage of cerebrospinal fluid from the internal auditory canal. Any residual neuroepithelium of the cristae of the three semicircular canals is destroyed by mechanical probing. The surgeon can feel the 4 mm hook drop into the ampullary ends of the bony canals (Fig. 40-6). This entire technique should be practiced in the temporal bone laboratory to gain familiarity with the anatomy and proficiency in this procedure.

After destruction of the vestibular end organs, the vestibule is usually packed with absorbable gelatin sponge (Gelfoam) or, preferably, a small fat graft from the ear lobe (Fig. 40-7). Some surgeons recommend the use of gentamicin or streptomycin-soaked Gelfoam in the medial aspect of the vestibule to guarantee destruction of residual neuroepithelium. As seen in Figure 40-8, the absence of a tissue graft of the open oval window results in a pneumolabyrinth postoperatively. Generally, this result does not cause a problem, but a tissue seal with fat or fascia provides a better barrier between the middle ear and cerebrospinal fluid spaces. Leakage of cerebrospinal fluid after aspiration of the vestibule should be repaired with a tissue seal. The tympanomeatal flap is returned to the posterior canal wall and held in place with packing, and the procedure is terminated.

FIGURE 40-8 Vestibule (V) remains in communication with middle ear (ME) 14 years after transcanal labyrinthectomy.

POSTOPERATIVE CARE

The degree of postoperative vestibular disturbance is positively correlated with preoperative residual vestibular function. That is, individuals with normal or near-normal caloric response preoperatively have a more severe reaction than individuals with minimal or no vestibular response. Third-degree nystagmus, nausea, and vomiting can be expected. Control of the vestibular symptoms may be achieved with promethazine or droperidol. Vestibular suppressants should be tapered as quickly as possible, given the evidence that they may impair or slow central compensation for unilateral vestibular ablation. Rapid advancement of physical activity should be encouraged, including sitting and ambulation with assistance in the first few days. The patient may be discharged when he or she is relatively self-sufficient and ambulating without assistance. This improvement may take 3 to 7 days.

At the first postoperative visit at 1 week, the packing is removed, and progressive activity is encouraged. The patient is seen 1 month postoperatively to evaluate residual symptoms, progress, and compensation, and to ascertain healing of the tympanic membrane and ear canal. At this time, there is usually no residual spontaneous nystagmus, and a caloric test of the ear that had surgery, using 20 mL of ice water and Frenzel’s lenses, is used to ascertain the completeness of unilateral vestibular ablation. Further follow-up depends on the patient’s progress.

SURGICAL COMPLICATIONS AND MANAGEMENT

HISTOPATHOLOGY OF LABYRINTHECTOMY

Postmortem histopathology of temporal bones from patients who, in life, underwent labyrinthectomy has been reported by Belal and Ylikoski,²⁰ Linthicum and associates,²¹ Pulec,²² and Schuknecht,²³ and all have reported examples of incomplete mechanical disruption of the vestibular end organ after transcanal labyrinthectomy. These results underscore the importance of proper exposure, removal of the utricle, and thorough probing of the ampullae. In an animal study of labyrinthectomy, Schuknecht²³ reported that the neuroepithelium of the posterior semicircular canal persisted in 10 of 24 ears. This fact argues for wider exposure of the vestibule by connecting the oval and round windows, and for selective destruction of the posterior ampullary nerve, as recommended by Gacek,²⁴ as an additional step to guarantee complete labyrinthectomy.

Linthicum and associates²¹ and Belal and Ylikoski²⁰ reported traumatic neuroma within the vestibule after labyrinthectomy (Fig. 40-9). Both groups interpret this finding as an indication of the superiority of the translabyrinthine vestibular neurectomy. In one case, a traumatic neuroma was also described after transmastoid labyrinthectomy and section of the superior vestibular nerve. In an experimental study in the cat, Schuknecht²³ reported no evidence of regeneration of vestibular nerve fibers or formation of traumatic neuroma after labyrinthectomy. In temporal bone specimens from human subjects who had undergone transcanal labyrinthectomy during life, degeneration of the vestibular nerve was seen in one, and a proliferation of nerve fibers was identified in another (Fig. 40-10). No evidence exists, however, to suggest that nerve fibers, whether residual or regenerative, can contribute to afferent vestibular input if the vestibular neuroepithelium distal to it has been destroyed.

FIGURE 40-9 Histopathology of superior vestibular nerve 36 months after transcanal labyrinthectomy in a cat. A, Unoperated control ear at the level of the normal macular utriculi (MU). B, In the ear that had undergone labyrinthectomy, there was moderate degeneration of vestibular nerve (VN), new bone and fibrous tissue within the vestibule (V), and no evidence of proliferation of remaining vestibular nerves.

FIGURE 40-10 Histopathology 4 months after left labyrinthectomy. A, Macular utriculi (MU) of the operated ear shows atrophy. The stroma of the macula is intact, however, and there has been proliferation of nerve fibers (NF) within it. B, Superior vestibular nerve and MU of the unoperated side appear normal.

Two patients are cited by Linthicum and associates²¹ as examples of failure of labyrinthectomy because of traumatic neuroma. In the first case, reported by Hilding and House,²⁵ the neuroma was uncovered at revision labyrinthectomy, but there was no evidence that the persistent symptoms resulted from the neuroma, rather than from residual neuroepithelium.

In the second case, reported by Pulec,²² a traumatic neuroma was identified by postmortem temporal bone histopathology in a patient with persistent vestibular symptoms for 10 years after labyrinthotomy, not labyrinthectomy. In addition, despite no response on the premortem caloric testing, the ampulla of the posterior semicircular canal was normal. In this case, the persistent vestibular symptoms probably resulted from residual vestibular neuroepithelium rather than from the traumatic neuroma.

RESULTS OF SURGERY

The reported results as measured by ablation of caloric function or cure of the patient have varied considerably. Linthicum and associates²¹ reported that only 17 (60%) of 25 patients who underwent labyrinthectomy were cured or improved by this approach; they advocated translabyrinthine nerve section as a more reliable method of ablating vestibular function. Ariagno¹⁵ found, however, a 98% success rate in controlling peripheral vestibular disorders through transcanal labyrinthectomy, emphasizing the need for total destruction of the vestibular end organs by joining the oval and round windows. Hammerschlag and Schuknecht²⁶ reported a cure of episodic vertigo in 120 (96.8%) of 124 patients by transcanal labyrinthectomy. The remaining four patients had continuing dysequilibrium, and three with persistent vestibular response by postoperative ice water caloric tests were cured by revision transcanal labyrinthectomy, resulting in an overall cure rate of 99%.

SPECIAL CONSIDERATIONS

The advent of cochlear implantation as a possibility for rehabilitation of profoundly deaf patients, and the fact that 10% to 40% of patients with Meniere’s disease have bilateral involvement require consideration of the implications for eventual implantation after any surgical procedure for management of vestibular disturbance. Chen and colleagues²⁷ reported on three temporal bone cases from patients who in life had undergone labyrinthectomy, two by the transcanal route and one by the transmastoid approach. Based on the patency of the cochlear duct, remaining spiral ganglion, and neural elements, and maintenance of the organ of Corti as evaluated by histopathologic study, these authors predicted that labyrinthectomy would not preclude subsequent cochlear implantation. In six patients who had undergone previous unilateral transmastoid labyrinthectomy, Lambert and coworkers²⁸ reported that round window electric stimulation resulted in a psychophysical response to stimulus in all patients and electrically evoked middle latency response in five of six patients. Kveton and associates²⁹ reported an ear deafened by transmastoid labyrinthectomy with subsequent successful cochlear implantation resulting in speech comprehension comparable to that of patients deafened by other causes.