An endolymphatic shunt is a surgical procedure in which a very small silicone tube is placed in the membranous labyrinth of the inner ear to drain excess fluid.
An endolymphatic shunt is placed as part of the treatment of Ménière's disease, a disorder of the inner ear whose causes are still unknown. Ménière's disease is characterized by the following symptoms:
- a rise in the level of endolymphatic fluid in the labyrinth of the inner ear
- hearing loss that comes and goes
- a sensation that the environment or oneself is revolving or spinning (vertigo)
- ringing, buzzing, or hissing noises in the ears (tinnitus)
- a feeling that the ears are blocked or plugged
Endolymphatic shunt surgery is one of the surgical procedures available to treat Ménière's disease, which is also known as endolymphatic hydrops. The surgery is based on the theory that the disorder causes the inner ear to become overloaded with fluid and that draining this fluid will relieve the symptoms. The fluid is drained by opening the endolymphatic sac, a pouch located next to the mastoid bone at the end of the endolymphatic duct. The endolymphatic duct is a canal that leads to the inner ear.
According to the National Institute on Deafness and Other Communication Disorders (NIDCD), there were an estimated three to five million cases of Ménière's disease in the United States in 1998, with nearly 100,000 new cases diagnosed annually. In most cases only one ear is affected, but as many as 15–40% of patients are affected in both ears. The onset of Ménière's disease occurs most often in adults between the ages of 20 and 50. Men and women are affected in equal numbers.
An endolymphatic shunt is placed with the patient under general anesthesia. The operation takes about two hours to perform. The patient is usually positioned lying on the back with the head turned to one side and the affected ear lying uppermost. The head is immobilized and supported with a pad or brace. The operation itself begins with opening the mastoid bone and identifying the endolymphatic sac. To find the sac, the surgeon removes the bony cover of the sigmoid sinus, which is an S-shaped cavity behind the mastoid bone. The surgeon leaves intact a small rectangle of thin bone called Bill's Island (named for Dr. William House). The sigmoid sinus is then collapsed with gentle pressure. The surgeon exposes the endolymphatic sac and makes an incision in it in order to insert the shunt.
The diagnosis of Ménière's disease is based on the patient's medical history, a physical examination , and the results of hearing tests, balance tests, an electronystagmogram, and imaging studies. An MRI or CT scan is performed to rule out a tumor as the cause of the patient's symptoms. A hearing test (audiogram) identifies the hearing loss that is typical of Ménière's disease. Balance function tests are administered to assess the patient's vertigo.
The patient is prepared for surgery by having the hair removed and the skin shaved over an area of at least 1.5 in (3.8 cm) around the site of the incision. A mild solution of soap and water is commonly used to cleanse the outer ear and surrounding skin.
The operated ear is covered with a Glassock dressing, which is a special dressing applied to keep pressure on the site to reduce swelling. There is usually some tenderness and discomfort in the operated ear and the throat (from the breathing tube inserted during surgery), which can be controlled by such analgesic medications as meperidine (Demerol) or oxycodone (Percocet).
There are few risks associated with endolymphatic shunt surgery. The operation is considered the first-line surgical treatment for Ménière's disease precisely because it is very safe. The chance of hearing loss from the procedure is about 0.5%.
Endolymphatic shunt surgery relieves the vertigo associated with Ménière's disease, with restoration of hearing dependent on the severity of the disease. The patient's ear may protrude slightly shortly after surgery but usually returns to its original position within two to three weeks after the operation. Numbness around the ear is a common complication that may last for several months.
Morbidity and mortality rates
Endolymphatic shunt surgery is considered a lowmorbidity procedure. It has been reported to achieve complete or substantial control of vertigo in 81% of patients, with significant improvement in hearing in about 20%. Overall, there is a 60% chance of curing the vertigo, a 20% chance that the attacks will remain at the same level of severity, and a 20% chance that the attacks will get worse. The patient's vertigo usually improves even if hearing does not improve.
There are several nonsurgical treatments recommended for patients with Ménière's disease:
- Vestibular suppressants. These are drugs designed to control vertigo attacks; they include mechzine (Antivert), diazepam (Valium), and dimenhydrinate (Dramamine).
- Diuretics. Medications that increase the body's output of urine can also help reduce the frequency of vertigo attacks in some patients by lowering the amount of fluid in the body.
- Dietary changes. Although the benefits of a low salt diet have not been confirmed by formal scientific research, many patients with Ménière's disease have noted that their symptoms improve when they restrict their salt intake.
- Steroids. Prednisone and other steroids have been used to treat patients in the early stages of Ménière's disease. Their use in this disorder, however, is still considered experimental as of 2003.
Surgical alternatives to the placement of an endolymphatic shunt include:
- Selective vestibular neurectomy. In this procedure, the surgeon cuts the vestibular nerve, which relays balance, position and movement signals from the inner ear to the brain. Vestibular neurectomy prevents the transmission of faulty information from the affected ear and eliminates attacks of vertigo in many patients.
- Labyrinthectomy. In this procedure, the membranous labyrinth of the inner ear is removed. Labyrinthectomy is more successful than other surgeries in eliminating vertigo, but the patient suffers complete and permanent loss of hearing in the operated ear.
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Brookler, K. H. "A Patient with Endolymphatic Hydrops Refractory to Shunt Surgery." Ear Nose Throat Journal 79 (July 2000): 493.
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American Academy of Otolaryngology—Head and Neck Surgery. One Prince Street, Alexandria, VA 22314. (703) 806-4444. http://www.entnet.org .
National Institute on Deafness and Other Communication Disorders (NIDCD). 31 Center Drive, MSC 2320, Bethesda, MD 20892-2320. (800) 241-1044. http://www.nidcd.nih.gov/ .
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"Ménière's Disease–Surgical Therapy." UPennHealth. <www.uphs.upenn.edu/balance/patient%20education%20brochures/Men ere's-Surgical%20Treatment.htm> .
Monique Laberge, PhD
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
An endolymphatic shunt is performed in a hospital or ambulatory surgery center on an outpatient basis. It is done by an otolaryngologist, who is a surgeon specializing in disorders of the ear, nose, and throat.
QUESTIONS TO ASK THE DOCTOR
- What are the alternatives to an endolymphatic shunt procedure?
- Will I regain my hearing if I have this surgery?
- Can I expect improvement in any of the other symptoms of Ménière's disease?
- How long will it take to recover from the surgery?
- How many endolymphatic shunts do you perform each year?