Labyrinthectomy

Anatomy and Physiology

The vestibular system consists of a paired set of organs located within the inner ears. Its unique anatomy consisting of multiple angles and turns can be described as labyrinthine, and thus the vestibular portion of the inner ear is often referred to as the labyrinth.

Each labyrinth consists of 5 organs: the superior, lateral, and posterior semicircular canals (SSC, LSC, and PSC, respectively), the utricle, and the saccule. The semicircular canals provide information about the rotational movements of the head.  The utricle and saccule provide information about linear movements of the head, with the five organs functioning together akin to a gyroscope to determine the position in space and relative movements of the head. The input from each labyrinth (right and left) corroborates one-another, and this information, as well as inputs from the visual and somatosensory systems, is processed in the brain balance centers. Lack of corroboration can lead to disequilibrium and vertigo.[1]

Indications

The dizziness resulting from a stable vestibulopathy (such as loss of a vestibular organ, or one-time damage to a vestibular organ) can typically be alleviated by central compensation, which can be facilitated by physiotherapy and rehabilitation. Diseases that cause unstable vestibulopathy (a progressive or otherwise changing abnormality of the vestibular apparatus, Meniere disease being the prototypical example) are less likely to be centrally compensated. Failing medical therapy and an extended course of vestibular rehabilitation, unstable vestibulopathy may need to be addressed by vestibular ablation.

Labyrinthectomy is one option for the surgical ablation of the affected organ(s) of the vestibular system, essentially converting an unstable vestibulopathy to a stable one. Other options include intratympanic gentamicin (otherwise described as chemical labyrinthectomy, intentionally introducing a vestibulotoxic agent to the affected vestibular apparatus), or a vestibular nerve section.[2][3]

Contraindications

Because labyrinthectomy necessarily causes total hearing loss in the operated ear, one of the primary contraindications for this procedure is serviceable hearing in the diseased ear. This contraindication becomes even stronger if the ear to be operated is the only hearing hear. More recently, however, this contraindication has eased somewhat because cochlear implantation has been shown to be an effective means of rehabilitating hearing in an ear that has undergone labyrinthectomy.[4] 

Generally, patients with a pure tone average threshold of at least 70 dB or greater, along with a word discrimination score of 30% or less, would be considered as candidates for labyrinthectomy. Nevertheless, serviceable hearing is subjective to the patient, and ultimately the decision to proceed with labyrinthectomy is based on the patient’s and the physician’s thoughtful discussion of risks versus benefits of surgery.

A successful labyrinthectomy procedure depends not only on the complete removal of diseased neuroepithelium from all five vestibular organs but also on the adequate central compensation to normal vestibular function on the opposite side. Therefore, preoperative vestibular testing is imperative to verify normal vestibular function in the non-operative ear. Preoperative counseling in patients undergoing labyrinthectomy for Meniere disease will need to consider the 10 to 40% possibility of future disease of the opposite ear despite normal function at the time of surgery.[5][6] 

The preoperative evaluation will also need to consider the possibility of poor central compensation. Negative indicators for central compensation are mostly centered on a patient’s ability to participate in the course of vestibular rehabilitative physical therapy. These negative indicators include increased age, visual problems, cognitive impairment, and contributors to a sedentary lifestyle such as obesity, arthritis, or lower limb dysfunction.

Equipment

The labyrinthectomy procedure is done under general anesthesia in an operating room. The surgeon will need an operative microscope, an otologic drill with appropriately-sized cutting and diamond burrs, an otologic instrument set, and a facial nerve monitor. Facial nerve monitoring can improve the safety and speed of otologic procedures.[7]

Personnel

As with any operation, the labyrinthectomy procedure requires a team approach for optimal outcomes. The surgeon must communicate with the anesthesiologist or nurse anesthetist, the circulating nurse, and the surgical technician to coordinate a smooth and expeditious procedure. The surgical time-out confirms the correct patient and laterality and ensures that all team members are in agreement regarding the surgical plan.

Preparation

Prior to the induction of anesthesia, the surgeon and anesthesia provider will discuss the need for facial nerve monitoring and avoidance of a long-acting paralytic during induction. Preoperative antibiotic prophylaxis is administered. Intravenous steroids can be given per surgeon preference. Once general anesthesia has been induced, and the patient has been intubated, the bed is turned 180 degrees. The surgical technician will move to the side opposite the ear to be operated, and the microscope will be at the head of the table.

With the goal of creating a sterile field that is free of hair, postauricular hair can either be shaved or separated from the field with adhesive drapes. Facial nerve monitoring electrodes are placed, and the proper equipment function is verified. Local anesthesia is typically injected into the EAC and postauricular incision (if used) to promote vasoconstriction and reduce pain.

Technique or Treatment

The labyrinthectomy procedure can be performed by either a transcanal approach or a transmastoid approach.[1][8] The transcanal approach is less invasive and requires less operative time; however, there may be a higher chance of incomplete removal of neuroepithelial tissue. The transmastoid approach is considered to be the gold standard for labyrinthectomy.[9] From an outcomes standpoint, vertigo control between transcanal and transmastoid approaches are equivalent and very high (100% transcanal; 95.5% transmastoid). Persistent disequilibrium seems to be significantly more common via the transcanal approach (62.5% transcanal; 22.7% transmastoid).[10]

Transcanal Labyrinthectomy

It begins as a long tympanomeatal flap centered over the posterior superior quadrant of the tympanic membrane. Once the flap has been elevated, the scutum may need to be curetted in order to completely visualize the stapes footplate and the round window niche. As the flap is being elevated and the scutum is curetted, care is taken to avoid injuring the chorda tympani nerve. The incudostapedial joint is then separated, the stapedial tendon is ligated, the incus is removed, and the stapes along with the footplate are gently rocked out of the oval window.

Removal of the promontory between the oval and round windows allows for adequate visualization of the vestibule. Care is taken not to suction the perilymph so as not to disrupt the positions of the membranous neuroepithelial tissue. A 4 mm right-angle hook is then extended superiorly medial to the horizontal facial nerve to gently excise the utricle neuroepithelium from the elliptical recess. The hook is then used to palpate and excise the ampullae of the superior and lateral semicircular canals.

Gentle suction is used to remove the saccule from the spherical recess taking care not to injure the medial wall of the vestibule and cause a cerebrospinal fluid leak from the internal auditory canal. The right-angle hook can then be used medial to the vertical facial nerve to palpate and excise the ampulla of the posterior semicircular canal. Alternatively, drilling of the bone posterior to the round window can identify the singular nerve which can subsequently be sectioned. Once the procedure has been completed, the middle ear is packed with gel-foam soaked in gentamicin to chemically ablate any remaining neuroepithelium that may have been missed.

Transmastoid Labyrinthectomy

It begins with a complete mastoidectomy. Exposure is obtained through a postauricular curvilinear incision, raising of anterior and posterior flaps at the level of the superficial temporal fascia, and a T-shaped incision through the periosteum with the top of the T at the linea temporalis and the vertical segment extending toward the mastoid tip. An anterior subperiosteal flap is elevated toward the ear canal until the edge of the bony canal has been reached, and the spine of Henle has been identified.

A posterior subperiosteal flap is elevated to allow for adequate exposure of the mastoid cortex and placement of a Wietlander retractor. A complete mastoidectomy is then performed, identifying the tegmen mastoideum superiorly, the sigmoid sinus posteriorly, and thinning the bony external auditory canal anteriorly. Medially, the lateral semicircular canal and the antrum are identified. At this point, the labyrinthectomy procedure begins. Using a 3 mm diamond burr, the air cells surrounding the otic capsule of the semicircular canals are removed. These include air cells lateral to the SSC and extending into the subarcuate area as well as air cells posterior to the PSC and extending superiorly to the crus communis. Once the semicircular canals have been identified, the labyrinth is typically first entered at the dome of the LSC.

Care is taken to enter LSC superiorly and to avoid drilling past the inferior edge of the lumen in order to minimize the chance of facial nerve injury. The LSC is followed anteriorly to its ampulla, which is signified by an obvious increase in caliber compared to the lumen of the canal itself.  The lateral semicircular canal is then followed posteriorly toward the dome of the PSC, where the lumen of the PSC is entered. This is followed inferiorly and slightly anteriorly until the ampulla is reached. As this is being done, care is taken to avoid drilling inferior to the inferior border of the lumen of the PSC in order to avoid possible injury to the jugular bulb. Also, note that the ampulla of the PSC is medial to the facial nerve.

The PSC is then followed superiorly to the crus communis, and the posterior limb of the SSC is identified. This is then traced superiorly and anteriorly toward the dome of the SSC. Care is taken to stay inferior to the superior border of the lumen to avoid injuring the tegmen. Note that drilling the SSC typically results in some bleeding from the subarcuate artery that can be stopped with bone wax or bipolar cautery. The SSC is then followed anteriorly until its ampulla. Drilling then continues deep to the LSC between the ampulla of the LSC and PSC to enter the vestibule widely. At this point, a small suction and a joint knife are used to gently scrape all neuroepithelial elements from the vestibule as well as all three ampullae. Gelfoam soaked with gentamicin can be used to pack the vestibule and ampullae based on the surgeon’s preference to chemically ablate any residual neuroepithelium.[11]

Complications

CSF Leak Typically caused by violating the macula cribrosa on the medial wall of the vestibule and allowing CSF penetration into the vestibule from the internal auditory canal.

Facial Nerve Injury is possible as neuroepithelial elements of the vestibule, as well as the PSC, lie medial to the course of the facial nerve. Great care must be taken when dissecting these areas, and powered instrumentation should be avoided for this portion of the procedure.

Disabling Chronic Disequilibrium is a rare unfortunate complication.

Cochlear Ossification and the subsequent inability to rehabilitate hearing by cochlear implantation could be considered a less frequently acknowledged complication of labyrinthectomy. Cochlear patency is typically preserved for many years after labyrinthectomy.[12] Violation of the internal auditory canal and disruption of the labyrinthine artery may predispose to cochlear ossification.[13]

Clinical Significance

The goal of the labyrinthectomy procedure is to ablate an unstable and dysfunctional vestibular system in order to promote central compensation for patients with episodic vertigo and/or baseline disequilibrium. As discussed earlier, total hearing loss in the operated ear is expected. Vertigo control rates are high (95 to 100%), but there is a significant possibility of persistent disequilibrium.

Enhancing Healthcare Team Outcomes

The otologic surgeon who would typically perform a labyrinthectomy likely works within a healthcare team to perform many other otologic procedures. If not, certainly, a working relationship needs to be established between the surgeon, the anesthesiologist, the circulating nurse, and the surgical technician. This will ensure proper preoperative preparations regarding antibiotic prophylaxis, steroid administration, and facial nerve monitoring concerns. This will also minimize delays resulting from a lack of proper supplies or equipment in the operating room.

Nursing, Allied Health, and Interprofessional Team Interventions

Unlike with many other otologic procedures, a patient undergoing a labyrinthectomy is expected to be admitted as an inpatient after surgery. The admission typically revolves around control of the expected postoperative vertigo. Patients who experience a sudden ablation of vestibular function will experience severe vertigo along with nausea and possible vomiting for 48-72 hours after the procedure. During this time, the surgeon will need to work with skilled nursing to control symptoms with medication as well as to ensure proper hydration of the patient. During admission, a referral can be made to physical therapy to begin the process of vestibular rehabilitation and lower extremity conditioning.

Nursing, Allied Health, and Interprofessional Team Monitoring

After labyrinthectomy, the monitoring of the patient is typically shared between the otologist and the audiologist. Assuming that vertigo has been controlled, the degree of residual disequilibrium needs to be assessed and addressed. If vertigo recurs, vestibular testing with the audiologist will need to be repeated to determine if there is a remaining vestibular function in the operated ear or if the opposite ear has become diseased. The patient’s ability to adapt to the loss of hearing will need to be assessed. Hearing rehabilitation options will be discussed with the audiologist. This discussion will include options such as a CROS-type hearing aid, a bone-anchored hearing aid, and/or cochlear implantation.