What Is Superior Canal Dehiscence Syndrome?
Superior canal dehiscence syndrome (SCDS) is a rare syndrome that is caused by an abnormal opening between the semicircular canal of the inner ear and the brain. This disease can result in hearing problems as well as balance problems for the patients. The uppermost semicircular in the upper part of the inner ear and the brain forms a connection in this condition; usually, there will be a separation between both the compartments.
During fetal development in such patients, there will be either abnormal thinness or incomplete closure of the bony canals of the inner ear, which is causing this condition. So in such patients, sound can leak through and repeat itself in the brain. This can result in problems with hearing and balance.
What Causes Superior Canal Dehiscence Syndrome?
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The real cause for superior canal dehiscence syndrome is unknown. But as this syndrome is caused by thinness or incomplete closure of the canal, it is assumed that the cause is congenital (present from birth) or happened during the development of the ear.
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In normal conditions, this canal is closed, forming a closed passageway, with sound coming through from one end (the stape bone at the oval window) and out the other way (through an opening in the inner ear), and the person will have normal balance and hearing.
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In people having this connection between the inner ear and the brain, there can be a sound leak that can reverberate in the brain; this will result in autophony (an abnormal sound of one’s voice), vertigo, and pressure in the ear.
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The other reason is that some people will have abnormal thinness of this bone by birth which is susceptible to trauma, infection, or age.
What Are the Symptoms of Superior Canal Dehiscence Syndrome (SCDS)?
The symptoms of superior canal dehiscence syndrome will affect hearing and balance to a different extent in different people and will include the following:
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SCDS-related Autophony - In these patients, they hear their own voices as disturbingly loud and distorted sounds deep inside the head as if relayed through a cracked loudspeaker. Even they will be able to hear the slightest of sounds as loud noise. They may even hear the creaking and cracking of joints, the sounds of their walking and running, their heartbeat, and the sound of chewing and other digestive noises. In this condition, the patient will be able to hear the motion of the eyeball within the socket, like “sandpaper on wood.” This symptom is one of the distinctive features of this condition and is almost exclusively associated with SCDS.
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Tullio Phenomenon - In this, the patient will have sound-induced balance loss. These patients will have a loss of equilibrium, nausea, or motion sickness triggered by normal sounds. The volume is necessarily not needed; even the sound of a plastic bag crackling, the sound of a coin tossing on the floor; a phone ringing; a knock at the door; or a patient's own voice can result in a loss of balance when this condition is present. Sound induces involuntary eye movements of the patient making the patient feel the world is tipping, clockwise or anticlockwise, depending on the dehiscence.
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Pulsatile Tinnitus - Pulsatile tinnitus is another typical symptom of superior canal dehiscence syndrome and is caused by the gap in the dehiscent bone allowing the normal pulse-related pressure changes within the cranial cavity to enter the inner ear abnormally.
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Low-Frequency Conductive Hearing Loss - It is present in patients with SCDS as the hole in the semicircular canal acts as a third window. The sound that enters the ear canal and middle ear are abnormally diverted into the intracranial cavity, where the vibrations are absorbed rather than being registered and read by the hearing center, the cochlea. The clinical sign of this condition is the ability of the patient to hear vibrations from the tuning fork, which is kept at the ankle bone.
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Headache and Migraine - This is seen as a result of strain in the adjacent structures of the face and neck for overcompensating for poor hearing of the affected ear.
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Brain Fog and Fatigue - This is due to the brain constantly working to maintain equilibrium when it is receiving confusing signals throughout the day.
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Hyperacusis - Is the hypersensitivity to noise and intolerance to normal sound from the environment.
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Oscillopsia - Is the illusion of stationary objects moving around.
How Is Superior Canal Dehiscence Syndrome Diagnosed?
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In order to diagnose SCDS, a detailed case history is taken by the doctor to understand the symptoms in detail.
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A thorough clinical examination will be done in order to rule out other causes.
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Following this, the clinician will order a series of tests for the diagnosis. Among the tests to diagnose SCDS, a CT scan of the temporal bone is one of them. But a CT scan will not produce a clear image, and even if there is a thin intact bone present, it may not be shown distinctly.
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The other tests include hearing tests, complete balancing tests, and a vestibular evoked myogenic potential (VEMP) test.
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The vestibular-evoked myogenic potential test is done by placing an electrode on one side of the neck or around the eyes. Following this, the sound is introduced into one ear, and the response is measured from the muscles of the neck or the eyes.
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Patients with SCDS show increased response to sound, which is measured from the muscles. This test helps identify the site of injury and hence the cause of SCDS.
What Are the Treatment Options for SCDS?
Most patients with SCDS do not require treatment as they learn to adapt to the condition by avoiding activities causing vertigo and oscillopsia. Also, patients will avoid places with loud noises. Using hearing protection can be effective when you expect loud noises. One can consult a certified vestibular therapist as they can provide patients with exercise that can help improve balance and reduce fall risk.
If the SCD is severe and is interfering with daily living, then in such cases plugging of the dehiscence through surgical repair may be needed. The most common surgical treatments are:
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Resurfacing or plugging the dehiscence from the middle cranial fossa approach.
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Plugging of the dehiscence from the mastoid approach.
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Reinforcement of the round window membrane.
Conclusion
Superior canal dehiscence syndrome is a condition that causes symptoms related to balance and hearing and is related to a rare syndrome known as superior canal dehiscence, in which communication is formed between the inner ear and the cranial cavity. The cause of this condition is mostly genetic or from trauma or infection. The patients will have autophony, vertigo, oscillopsia, and other symptoms. As it is a defect, the treatment for this condition would be a surgical correction. If you or any known person has these symptoms, consult a doctor to receive the right treatment.
