Labyrinthectomy

Background

Labyrinthectomy is an effective surgical procedure for the management of poorly compensated unilateral peripheral vestibular dysfunction in the presence of a nonserviceable hearing ear.[1, 2] Relief from vertigo is achieved at the expense of the residual hearing in the ear to be operated. Hence, the procedure is reserved for patients with nonserviceable hearing.

The basic principle of labyrinthectomy is to symmetrically open all the semicircular canals and vestibules; the landmarks should be preserved until the end of labyrinthectomy. After exposing all the ampullae and vestibules, the five individual groups of neurosensory epithelia are excised under direct visualization.[3] This is performed to eliminate abnormal vestibular input from the diseased ear.[4] See the images below.

There are two techniques for vestibular end organ ablation: transcanal labyrinthectomy and transmastoid labyrinthectomy. Transcanal labyrinthectomy[5] is an effective treatment option for the management of poorly compensated unilateral peripheral vestibular dysfunction in the presence of ipsilateral, profound, or severe sensorineural hearing loss. The modern transcanal labyrinthectomy for the management of unilateral peripheral dysfunction was introduced in the 1950s by Schuknecht[6] and Cawthrone.[2, 7]

Transcanal labyrinthectomy has several advantages, including the following[2, 8] :

• Less invasive than transmastoid labyrinthectomy

• Direct approach to vestibular end organ

• Shorter operating time than transmastoid labyrinthectomy

• Lower morbidity than transmastoid labyrinthectomy

However, this approach does have some disadvantages.[8, 4] Transcanal exposure is limited as compared to that in transmastoid labyrinthectomy. There is a significant incidence of incomplete labyrinthectomy in the hands of an inexperienced surgeon. In addition, reaching the ampulla of posterior semicircular canal is difficult because this maneuver is performed with blind probing.

Indications

Labyrinthectomy is indicated for poorly compensated unilateral peripheral vestibular dysfunction in the presence of a nonserviceable hearing ear.

Vestibular disorder should be given appropriate medical treatment before labyrinthectomy. Rehabilitative vestibular therapy also should be attempted before labyrinthectomy.

Labyrinthectomy should be done only in cases with unilateral vestibular dysfunction with ipsilateral severe hearing loss.

Alternative techniques for labyrinth destruction should be considered in young healthy individuals and in patients with bilateral vestibulocochlear disorder.[4]

Indications for the transmastoid approach include the following[1] {ref913-INVALID REFERENCE}:

• Delayed onset of vertigo syndrome

• Posttraumatic vestibular dysfunction

• Unilateral Meniere disease[9, 10]

• Transcanal labyrinthectomy failures

Contraindications

Labyrinthectomy is contraindicated when the affected ear is the only hearing ear. In patients with serviceable hearing, chemical labyrinthectomy or vestibular nerve sectioning should be considered.[4]

Relevant Anatomy

The anatomy of the inner ear consists of the bony labyrinth, a system of passages making up the following 2 main functional parts: (1) the cochlea, which is dedicated to hearing, and (2) the vestibular system, which is dedicated to balance. The inner ear is found in all vertebrates, with substantial variations in form and function. The inner ear is innervated by the eighth cranial nerve in all vertebrates. See the image below.

The osseus labyrinth consists of the cochlea, vestibule, and semicircular canals (see the image below). These bony cavities are lined with periosteum and contain perilymph. The fenestra vestibuli or oval window is an opening in the lateral wall of the vestibule of the osseous (bony) labyrinth. It articulates with the footplate of the stapes from the middle ear and opens into the fluid-filled inner ear.

For more information about the relevant anatomy, see Inner Ear Anatomy and Ear Anatomy.

Patient Education & Consent

Preoperative counseling[2] should include the following discussions with the patient:

• Information about the natural history of the vestibular disease

• Total hearing loss on the operated side

• Persistence of tinnitus after surgery

• Presence of postoperative vertigo for several days

• Permanent disability, which may require rehabilitation

• Risks of surgery like facial paresis or paralysis, cerebrospinal fluid leak or meningitis, and tympanic membrane perforation

• Failure of the procedure to achieve desired results and need for an alternate procedure

• Consent to harvest fat graft if required

Pre-Procedure Planning

Preoperative evaluation should include the following[2, 4] :

• Thorough otorhinolaryngological examination

• Audiological tests: speech discrimination and pure tone audiometry

• Vestibular function tests: caloric test, electronystagmography, positional tests

• Neurological examination to rule out any concurrent neurological disorders

• Radiographic assessment: computed tomography scan and magnetic resonance imaging

Equipment

Necessary equipment includes the following:

• Microdrill, different size cutting and polishing burrs

• Ear surgery microinstruments (eg, 4-mm right-angled hook)

• Facial nerve monitor

• Postaural retractors

Patient Preparation

Anesthesia

Labyrinthectomy should be done under general anesthesia because of the violent vestibular response during the removal of the vestibular end organs.

Revision labyrinthectomy in an ear with minimal residual vestibular function is done under local anesthesia. This may help to locate the site of residual vestibular function during surgery.

Positioning

The patient is placed in the supine position on the operating table, with reverse Trendlenberg tilt and extension of the neck. The head is turned away from the surgeon, with the ear to be operated facing up.[11] The patient is draped with a craniotomy type drape that has a large clear window to visualize the face.[3]

Monitoring & Follow-up

Antibiotic therapy is required. An antiemetic should be given routinely until nausea and vomiting cease. Some patients may require vestibular sedative medication for a few weeks.

The pressure bandage is removed after 24 hours and sutures are removed on postoperative day 7.

Patients should be gradually mobilized and physiotherapy exercises should be started. Patients should be encouraged to walk and take an active role in their rehabilitation.

Patients should not drive until they are free from attacks of spontaneous vertigo for at least 3 months and can make head movements without any sensation of unsteadiness.

Complications

Cerebrospinal fluid leak can occur when the cribrosa area is fractured. It can be managed by sealing the vestibule with tissue graft or subcutaneous tissue.

Failure to locate the utricle is a possible complication. While aspirating the perilymphatic fluid from the vestibule, the utricle usually retracts superiorly to lie medial to the horizontal segment of the facial nerve. This can be managed by using a utricular hook. Removing bone from the inferior aspect of the oval window and connecting it to the round window will improve access to the vestibule.

The horizontal segment of the facial nerve may be injured during transcanal labyrinthectomy. This can occur while removing the utricle and is managed according to the grade of injury. An intraoperative facial nerve monitor is used to prevent this complication.

Postoperative disequilibrium is managed by vestibular rehabilitation therapy and by occasional vestibular suppressants.

The incidence of incomplete labyrinthectomy is less than 5%. It is managed according to persistence of postoperative symptoms. Incomplete labyrinthectomy may require revision surgery or transmastoid labyrinthectomy and labyrinthine vestibular nerve resection.[2]

Approach Considerations

Labyrinthectomy is usually performed using the transcanal approach. The transmastoid (postaural) approach may be required in patients with a narrow meatus.

Transcanal Approach

In the transcanal approach, an anteriorly based tympanomeatal flap is elevated and the posterior aspect of the bony tympanic annulus is curetted to visualize the stapes foot plate. The horizontal segment of the facial nerve, stapes foot plate, and round window area should be completely visible to proceed further.

After removing the incus, the stapes tendon is sectioned; it should be removed carefully without fracturing it. The oval window is enlarged at its anterior and inferior aspects. The oval and round windows are connected to remove a segment of promontory using drill.

Near the posterior end of the round window niche, posterior ampullary nerve is exposed and sectioned.[2] The vestibule and basal turn of cochlea are exposed widely to create a common cavity. The utricle and saccule are scraped from the walls of the vestibule by using a right-angled hook. Probing is done to determine the locations of the ampullae of semicircular canal.[4]

After destruction of the end organ, the vestibule may be filled with a gelatin sponge (optionally soaked in gentamycin or streptomycin[6] or fat graft from the ear lobe.[2]

Cerebrospinal fluid leaks should be repaired with tissue seal. The tympanomeatal flap should be placed against the posterior canal wall and ear canal packed with the gelatin sponge.

Transmastoid Approach

In the transmastoid approach, a postaural incision is made and the mastoid cortex is exposed. A simple cortical mastoidectomy is performed with a large cutting burr, operating microscope, and suction irrigation. The aditus ad antrum is widened to visualize the short process of incus.[12]

The superior and posterior perilabyrinthine air cell tracts and retrofacial air cells are removed carefully to skeletonize the bony labyrinth; the facial nerve is then identified.[1, 3] The tegmen mastoideum is thinned with a medium diamond burr . Medium cutting burrs are used on the bony labyrinth because the bone is very hard. Continuous suction irrigation is used to remove bone dust as drilling is continued.[13] While working near the facial nerve, diamond burrs and copious irrigation should be used.[11]

The labyrinthectomy is started by drilling over the superior aspect of the lateral semicircular canal anteriorly and drilling is carried out towards the posterior semicircular canal. The lateral semicircular canal, which appears as a blue line, is opened along its superior surface. The inferior surface should be preserved as a landmark for the facial nerve.[1]

The drilling is continued in the posterior direction to open the posterior semicircular canal. The drill is then carried superiorly until the common crus and the superior semicircular canal is identified and opened. Anteriorly, the neuroepithelium of the superior and lateral ampulla is identified and dense labyrinthine bone is removed to open the vestibule.[1, 3]

The posterior semicircular canal is followed inferiorly and medial to the facial nerve to visualize the posterior canal ampulla. The portion of the posterior semicircular canal extending under the genu of the facial nerve should be drilled with a diamond burr. The horizontal segment of the facial nerve is then skeletonized.[1, 3]

During labyrinthectomy, bone should be preserved in the following regions[13] :

• Over the inferior wall of the lateral canal, to protect the second genu of the facial nerve

• Over the inferior wall of the posterior semicircular canal, to protect a high riding jugular bulb

• Over the medial wall of the superior semicircular canal ampullae, to protect the facial nerve anterior to the superior vestibular nerve at the fundus of the internal auditory canal

The bony dissection is complete when the neurosensory epithelium of the three ampulla, utricle, and saccule are visualized. After exposing all five portions of neurosensory epithelium, they are removed with a sickle knife, taking care not to rupture the underlying bony cribrosa.

Penetration in this area may cause cerebrospinal fluid leak. If there is cerebrospinal fluid leak, it should be repaired. Small leaks can be closed with bone wax and large defects are managed by obliterating the vestibule with muscle plug.[1, 3]

An attempt should be made to remove every vestige of neuroepithelium because a viable remnant may subsequently give rise to spontaneous, neuronal activity and continuation of vertigo. The surgical defect is washed with saline. The mastoid cavity is closed in layers. A standard mastoid head bandage is applied.[11]