Endolymphatic Shunt Placement 

Updated: Sep 05, 2018
Author: Matthew Ng, MD; Chief Editor: Arlen D Meyers, MD, MBA 

Overview

Background

Endolymphatic sac (ES) shunt surgery is a treatment for medically refractory disabling vertigo in Meniere disease, which is an inner ear disorder that features the symptomatic tetrad of episodic vertigo, aural fullness, fluctuating sensorineural hearing loss, and tinnitus.

The pathologic correlate to Meniere disease is endolymphatic hydrops, a dilation of the endolymphatic compartment of the inner ear, both in the cochlea and vestibule.[1, 2] This suggests an accumulation of endolymph. It is unknown whether the accumulation of endolymph results from overproduction or underresorption of endolymph. The precise etiology of Meniere disease is still unknown, even after a century and a half since Prosper Ménière first described the syndrome.[3]

Endolymph is produced by the stria vascularis and flows toward the endolymphatic sac, where it is resorbed. The endolymphatic sac has been the center of attention for the treatment of Meniere disease. If Meniere disease is related to an excessive accumulation of endolymph, the basis for endolymphatic sac surgery would be to surgically release the endolymphatic sac from its bony and dural confines to relieve the pressure via decompression or to incise the sac to drain the endolymph via shunting.

Surgery on the endolymphatic sac for the control of vertigo dates back to 1927, when it was performed by Georges Portmann.[4] He believed that Meniere syndrome resulted from overpressure of the endolymphatic fluid due to either an endolabyrinthine or extralabyrinthine cause. He used the term “aural glaucoma” to describe the situation in the inner ear. In his procedural descriptions, he simply incised the endolymphatic sac and allowed the clear endolymphatic fluid to drain. In this manner, he successfully treated numerous patients with vertigo.

The endolymphatic sac’s role in Meniere disease was more convincing after surgical obliteration or occlusion of the endolymphatic duct and sac led to a histologic endolymphatic hydrops in animal studies.[5, 6] Surgeries either to surgically open the endolymphatic sac and stent the lumen of the sac open with a shunt or to simply decompress the sac were performed with successful control of vertigo in Meniere disease.

Studies have demonstrated endolymphatic sac shunting to be effective in control of the vertigo in Meniere disease in 50%–75% of patients.[7, 8, 9, 10, 11, 12] In fact, it appears that endolymphatic sac decompression is as effective as endolymphatic sac shunting for control of vertigo.[13, 14, 15, 16]

The precise mechanism by which endolymphatic sac surgery helps to control the vertigo is unknown. However, endolymphatic sac surgery stands as the only surgical nonablative option for the treatment of Meniere disease. Thus, hearing can be preserved with such an operation, in contradistinction to the ablative surgical options.

Indications

Endolymphatic sac shunting is indicated for the control of the disabling vertigo of Meniere disease that has failed to improve with medical therapy. The side of involvement in unilateral Meniere disease should be clearly evident based on audiography and auditory symptoms, such as tinnitus and aural fullness. The patient should meet the most current criteria for the diagnosis of Meniere “definite” disease.[17] If bilateral Meniere disease is present, endolymphatic sac surgery is performed on the worse offending symptomatic side.

Medical management of Meniere disease includes a low-salt diet and diuretics. Other adjunctive medical options include vasodilators, systemic or intratympanic corticosteroids, and allergy or immune-mediated treatment. Vestibular suppressants and sedatives are used for symptomatic control of vertigo. If these are not sufficient to control the episodic, disabling vertigo, either nonablative or ablative therapies may be considered.

Ablative treatment involves destruction of the neuroepithelium or sensory structures of the inner ear (deafferentation). Therefore, permanent hearing loss and vestibular dysfunction can be expected after such therapy. Ablative procedures include intratympanic gentamicin (chemical labyrinthectomy), surgical labyrinthectomy, and vestibular nerve section. The only nonablative treatment is endolymphatic sac surgery.

Contraindications

Patients who do not fulfill the diagnostic criteria of “definite” Meniere disease should not be considered for endolymphatic sac shunt surgery. Patients with vertigo due to nonvestibular causes or central nervous system abnormalities should not undergo endolymphatic sac surgery.

Patients with definite Meniere disease whose condition is well-controlled with medical therapy should not undergo endolymphatic sac shunt surgery. These include patients with infrequent vertiginous attacks who can still carry on daily life activities, relatively uninterrupted by the dizziness. Patients who are chronically imbalanced and affected with disequilibrium should not undergo endolymphatic sac surgery, as these symptoms result from to end-organ vestibular damage due to long-term Meniere disease.

Endolymphatic sac surgery is not used to reverse longstanding hearing loss, to eliminate aural fullness, or to alleviate the tinnitus of Meniere disease.

Technical Considerations

Surgical access to the endolymphatic sac is via a postauricular transmastoid extradural approach. Standard mastoidectomy procedures are followed with the additional steps of skeletonization of the sigmoid sinus extending inferiorly toward the jugular bulb, sinodural angle, and the posterior fossa dura that lies between the sigmoid sinus and posterior semicircular canal. The endolymphatic sac is extradurally located on the posterior fossa dura in the infralabyrinthine region as a dural duplication or thickening.

Extradural location of the endolymphatic sac Extradural location of the endolymphatic sac

The decision by the surgeon to proceed with either endolymphatic sac decompression or endolymphatic sac shunt placement to the mastoid depends on surgeon preference, experience, and clinical outcomes.

Potential structures at risk for injury include posterior semicircular canal leading to fenestration and labyrinthine injury, posterior fossa dura leading to cerebrospinal fluid (CSF) leak, facial nerve leading to paralysis, and sigmoid sinus leading to hemorrhage.

Outcomes

Studies have demonstrated endolymphatic sac shunting to be effective in control of the vertigo in Meniere disease in 50%–75% of patients.[7, 8, 9, 10, 11] In fact, it appears that endolymphatic sac decompression is as effective as endolymphatic sac shunting for control of vertigo.[13, 14, 15]  During endolymphatic sac shunt placement, consideration may be given to the local application of steroids and intra-saccular infiltration with steroids, which have been reported to increase vertigo control rates compared to sac shunt placement alone.[18, 19]

 

 

 

Periprocedural Care

Patient Education & Consent

When endolymphatic sac surgery is indicated, the surgeon should explain to the patient, in the simplest terms, that the purpose of the surgery is to access that part of the inner ear putatively responsible for drainage or absorption of endolymph. By removing the surrounding bone, external pressure is relieved from the endolymphatic sac and duct. By creating an opening into the sac and placing a silicone shunt, a portal will be created for continuing drainage of endolymph into the mastoid cavity.

Potential risks and complications include bleeding, infection, CSF leak, dizziness, hearing loss (total or partial), facial paralysis, and failure to achieve improvement in the disabling vertigo. Risk of hearing loss has been estimated to be 1%–2% of endolymphatic sac cases.

Options and alternatives should be discussed in the preoperative counseling period. Usually, if a patient with Meniere disease has decided to consider endolymphatic sac surgery, the only other treatment options include ablative-type interventions to control the disabling vertigo. These include intratympanic gentamicin, surgical labyrinthectomy, and vestibular nerve section.

Postoperative instructions are given to the patient prior to surgery. This will assist patients in their preparation for surgery. Typically, after uneventful surgery, the patient can be discharged the same day of surgery. The patient may be kept overnight in the hospital for observation if any complications are encountered during the surgery, such as CSF leak or sigmoid sinus injury. Mastoid pressure dressings are kept on for 24 hours. Local wound care is administered as appropriate.

Pre-Procedure Planning

Prior to surgery, audiogram is obtained to document the hearing status. The audiogram can be used to assess hearing changes as a result of the surgery and as a baseline to monitor future hearing changes as the disease progresses.

In cases of unilateral Meniere disease, VNG with caloric testing is performed to determine if contralateral vestibular hypofunction is present.  Further evidence of contralateral Meniere's disease may be evidenced by audiogram that shows a low tone sensorineural hearing loss or abnormal contralateral electrocochleography or vestibular-evoked myogenic potentials. If this is the case, the presence of contralateral subclinical endolymphatic hydrops is a distinct possibility. Clinical suspicion of bilateral Meniere disease may arise if there is aural fullness, tinnitus, or an incipient low-tone sensorineural hearing loss in the contralateral ear. If bilateral Meniere disease is present, ablative procedures are avoided to prevent bilateral vestibular hypofunction and chronic imbalance, disequilibrium and oscillopsia.

Temporal bone CT scan should be obtained prior to surgery to determine whether the sigmoid sinus is anteriorly situated, which will require more aggressive skeletonization of the sigmoid sinus with decompression and posterior retraction to gain access to the endolymphatic sac. Mastoid pneumatization is assessed to determine the ease of exenterating the air cells just before reaching critical structures. Jugular bulb position is checked to make sure that it is not high-riding so that inadvertent injury will be avoided as bone removal over the sigmoid sinus is undertaken adjacent to the mastoid tip area. The vestibular aqueduct is assessed to make sure that it is not hypoplastic. This would make identification of the endolymphatic sac more difficult. The position of posterior semicircular canal relative to the endolymphatic sac is assessed so that inadvertent fenestration of the canal will be avoided.

Equipment

Surgical instrumentation required for endolymphatic sac surgery is the same as that used for chronic ear and lateral skull base surgery (high speed otologic drill, operating microscope and facial nerve monitor). Facial nerve monitoring would be helpful particularly when bone removal and dissection are undertaken adjacent to the retrofacial air cells. The most vulnerable area of the facial nerve at risk is the mastoid segment of the facial nerve.

Patient Preparation

General anesthesia is administered during endolymphatic sac surgery. The use of muscle paralytics is avoided for intraoperative facial nerve monitoring and stimulation.

Patient positioning during endolymphatic sac surgery is the same as for other transmastoid neurotologic surgeries. After induction of general anesthesia, the operating table is turned 180 degrees. The anesthesiologist is situated at the foot of the bed. The surgeon is at the head of the bed. A pillow is placed under the knees to prevent strain on the patient’s lower back lying supine. Patient is strapped across the upper torso and hips to avoid patient movement during table rotation. The patient’s head is turned opposite the operation side. There is no need for head fixation with pinions.

Anesthesia

Local anesthetic with vasoconstrictor (eg, 1% lidocaine with 1:100,000 epinephrine) is used to infiltrate the planned postauricular incision site for better hemostasis.

Monitoring & Follow-up

Postoperative monitoring largely depends on whether any complications were encountered during surgery. If a dural or sigmoid sinus tear was encountered, the patient should be monitored closely for acute neurologic changes or an expanding wound hematoma. Postoperative vertigo should be assessed with examination looking for irritative nystagmus that might indicate injury to the posterior semicircular canal. Facial nerve function should also be assessed.

Postoperative audiography is obtained 2 months after surgery to document hearing. At this time, the patient will also be able to discern whether the operation has been effective and has reduced the frequency of vertiginous attacks.

 

Technique

Approach Considerations

Complete mastoidectomy is performed with the additional steps to skeletonize the sigmoid sinus from sinodural angle inferiorly toward the jugular bulb and additional bone removal posterior to the sigmoid sinus will assist in depression of the sigmoid sinus to obtain a better surgical view of the endolymphatic sac.   The posterior fossa dura anterior to the sigmoid sinus is also skeletonized. The anterior limit of dissection is the posterior semicircular canal and mastoid segment of the facial nerve. There is no need to blue-line the posterior semicircular canal.

One of the key anatomical landmarks used in endolymphatic sac surgery is Donaldson's line. This is an imaginary line drawn posteriorly from the course of the horizontal semicircular canal. The line should course perpendicular to that of the posterior semicircular canal. The endolymphatic sac is located inferior to this line.

Donaldson line used to approximate location of end Donaldson line used to approximate location of endolymphatic sac.

Endolymphatic Shunt Placement

With the patient’s head turned opposite the side of the affected ear, the entire auricle and postauricular area is prepared and draped. Local anesthetic with vasoconstrictor (eg, 1% lidocaine with 1:100,000 epinephrine) is injected in the area of the planned postauricular incision. The incision is carried back behind the auriculocephalic crease the same distance as that for routine mastoidectomy for chronic ear disease, approximately 1 cm.

The plane lateral to the temporalis fascia is entered.

A periosteal T-shaped incision is created along the linea temporalis. A perpendicular incision from the linea temporalis incision is extended inferiorly toward the mastoid tip.

The musculoperiosteal flap is elevated forward until the posterior bony external auditory canal is reached. The remainder of the musculoperiosteum is elevated posteriorly and superiorly to expose the lateral mastoid cortex in preparation for mastoidectomy.

Mastoidectomy is commenced with the otologic high-speed drill using cutting burs for aggressive bone removal and using diamond burs as the approach nears critical structures. The tegmen mastoideum, sigmoid sinus, and sinodural angle are skeletonized, and the posterior bony ear canal wall is thinned. The mastoid tip air cells are opened to the level of the digastric ridge, which should approximate the level of the descending segment of the facial nerve as it courses toward the stylomastoid foramen.

Bone removal anterosuperiorly proceeds toward the mastoid antrum as Koerner septum is identified and opened. The prominence of the horizontal semicircular canal is identified. The zygomatic root toward the epitympanum (posterior epitympanotomy) is opened to identify the body and short process of the incus that will provide additional landmarks for orientation within the mastoid.

Bone removal over the sigmoid sinus can now continue inferiorly toward the jugular bulb. The mastoid segment of the facial nerve is skeletonized. This will assist in locating the retrofacial air cells and protecting the facial nerve from injury.

Using the prominence of the horizontal semicircular canal, Donaldson's line is identified to approximate the anticipated position of the endolymphatic sac. The endolymphatic sac should be located inferior to this line.

The endolymphatic sac usually presents as a dural duplication or dural thickening during exposure of the posterior fossa dural plate between the sigmoid sinus posteriorly and the posterior semicircular canal anteriorly. Removal of the retrofacial air cells, when present, will help gain more exposure to locate the endolymphatic sac. The endolymphatic sac is typically located deep and inferior to the posterior semicircular canal (infralabyrinthine). When the endolymphatic sac is located, it can be followed forward toward the endolymphatic duct that courses just medial of the posterior semicircular canal.

Once the endolymphatic sac is identified, the sac may be incised with a sharp sickle knife, and the lumen, characterized by its glistening and shiny appearance, is entered with an annulus elevator or blunt probe.

The right endolymphatic sac is opened. Shunt may b The right endolymphatic sac is opened. Shunt may be placed inside the lumen of the sac.

A silicon sheet (thickness 0.010 in or 0.05 mm) is cut and positioned inside the lumen. A commercially available shunt may also be used . There is usually no need to secure this silicone fashioned shunt.

The musculoperiosteal flaps are then re-approximated and sutured together. The postauricular tissues are closed in layered fashion.

A mastoid pressure dressing is placed.