The Department of Otolaryngology-Head & Neck Surgery

SUPERIOR CANAL DEHISCENCE SYNDROME

Some patients note a strange set of symptoms: Loud noises cause them to suffer sudden vertigo and blurred vision. Their hearing for internal noises (like a heartbeat and the grating of knee joints) is much better than normal. Until recently, these complaints were often considered psychosomatic.

One of the early achievements of our lab was defining a particular balance disorder that had never been described before, a discovery that took place in 1995. After assembling a range of clues, we determined that the condition, which involves a tear in the uppermost canal of the vestibule of the inner ear, occurs because the bony surface of the canal never grew to proper thickness during development. We named the condition superior canal dehiscence syndrome (a “dehiscence” is a hole). Then, we took our findings a step further and established a treatment for patients who suffer from the condition.

MENIERE’S DISEASE

Our lab has made great strides in improving the treatment of another balance disorder known as Ménière’s disease, which affects as many as 5,000,000 people worldwide. As of today, no one knows why people with Ménière’s disease accumulate fluid in the inner ear, but the effects are clear: fluctuating hearing loss, lack of balance and periods of terrible vertigo.

Many patients with Ménière’s disease are treated with dietary changes and diuretics to eliminate excess fluid, but that therapy doesn’t work for all patients. Endolymphatic sac surgery was offered by many centers, but results have been inconsistent. In extreme cases, surgery to cut the vestibular nerve or remove the vestibular part of inner ear solves the problem, but at the cost of major surgery and a chance or certainty of hearing loss.

Several years ago, doctors realized that gentamicin, an antibiotic commonly used for systemic infections has the side effect of knocking the vestibular structure out of commission by damaging hair cells.

Although gentamicin toxicity can itself be a cause of vestibular disorders, hearing loss and vertigo, this drug can be used to effectively and safely treat Meniere’s disease. Key to this concept is that the vertigo of intractable Meniere’s is due to fluctuation in vestibular function in the affected ear. By reducing or destroying residual vestibular hair cell function, gentamicin Adapted for use in treating Meniere’s disease, the medication is give by small injection directly into the ear. Though the treatment worked well to eliminate the debilitating spells of dizziness, it had the drawback of causing hearing loss in ten percent of patients.

Through work in the lab, our team has improved that treatment, known as intratympanic gentamicin, by determining that a lower dose of the drug can also be effective. In more than 100 patients we’ve treated during the last eight years with the low-dose version of the therapy, we’ve seen vertigo cured 90 percent of the time, results that equal the effectiveness of surgery. Most importantly, the incidence of hearing loss has been reduced substantially.

VERTIGO DUE TO AN OPENING IN THE BONE OVERLYING THE SUPERIOR SEMICIRCULAR CANAL

We have identified a syndrome in which vertigo and imbalance are triggered by loud noises or pressure in the affected ear. These symptoms are due to an opening in the bone overlying one of the inner ear balance canals. We believe that such an opening may result from congenital problem in the development of the inner ear, from certain infectious diseases, and/or from trauma. While this syndrome has only recently been identified, our studies of past records and of temporal bones (the bones containing the inner ear hearing and balance organs) indicate that the syndrome has been present, but not specifically identified in the past.

This syndrome produces some very specific symptoms. Patients can experience vertigo (an illusion of motion) caused by noises or pressure in the ear. The noises that can provoke such symptoms include loud music, being in a noisy environment such as a sports event, sounds on the telephone such as the dial tone or a busy signal, and sounds made by the patient such as singing at certain pitches. The pressure symptoms that can provoke the symptoms include pushing on the outer aspect of the ear, blowing through the nose while pinching the nostrils, and straining while lifting heavy objects. In addition to these symptoms that occur in specific association with the stimuli just described, patients with this syndrome may experience a generalized and more constant sense of disequilibrium and unsteadiness.

The diagram above shows the structures of the inner ear. The inner ear balance organs consist of three semicircular canals (the horizontal, posterior, and superior canals) that are located at roughly right angles to one another. These balance canals give the brain information related to the angular motion of the head. They function somewhat like a gyroscope in an airplane. The otolith organs (utriculus and sacculus) are the other balance organs in the inner ear. They give the brain information related to linear movements of the head and to the orientation of the head relative to gravity.

CT image in the plane of the superior semicircular canal of a normal patient. Note that bone covers the circumference of the canal. An air cell is visualized in this bone.

These inner ear balance receptors are ordinarily encased in very dense bone. If there is an opening (dehiscence) in the bone surrounding one of the balance canals, then this canal can be activated by stimuli other than head movements. The balance canal with such an opening can now respond to loud sounds and to pressure in the ear. Activation of a balance canal in this fashion results in movements of the eyes in the plane of the affected canal. This abnormal activation of the balance canal results in vertigo and in a sensation of motion of objects that are known to be stationary.

CT image in the plane of the superior semicircular canal of a patient with dehiscence of bone overlying this canal.

The syndrome we have identified is due to an opening in the bone overlying the superior semicircular canal. A diagram of the eye movements that can be induced by sound or pressure in the affected ear of a patient with this disorder is shown below.

Click on eye image to view movie

The eye movements that are induced by sound and/or pressure in the affected ear(s) of these patients are "to-and-fro" eye movements termed nystagmus. Such eye movements are made up of slow and fast components. The diagram above shows the direction of the slow components of the eye movements evoked by loud sounds in the right ear of a patient with an opening in the superior semicircular canal on that side. Note that the eyes movement upward and away from the stimulated ear. The fast components of the evoked eye movements are in the same plane but in the opposite direction.

These eye movements can be observed during clinical testing by administering tones over the frequency range of 500 – 2000 Hz with intensities of 100 – 110 dB. Similar eye movements can, in some cases, also be seen with pressure on the external ear or with blowing the nose while pinching the nostrils. The eye movements are best observed when the patient is wearing Frenzel lenses (20x magnifying lenses that enlarge the image of the eyes for the examiner but which blur vision for the patient and thereby prevent the nystagmus from being suppressed by looking at an object).