This topic provides information about superior canal dehiscence (SCD), sometimes called superior semicircular canal dehiscence (SSCD).
What is superior canal dehiscence?
Superior canal dehiscence is an opening or extreme thinning in the bone of the superior semicircular canal of the inner ear. The superior semicircular canal is one of the three fluid-filled bony canals located in the inner ear. They are responsible for sensing movement of the head in order to maintain balance.
Superior canal dehiscence is a rare condition. Even more rare is a dehiscence of the other two semicircular canals, the horizontal and posterior canals.
In a normal inner ear there are two openings for which sound pressure enters, the oval window and the round window. In cases of superior canal dehiscence, the bone opening and/or thinning of the superior semicircular canal creates a third opening. This third opening creates a physiological change in the inner ear.
What causes superior canal dehiscence?
There are several proposed theories for the cause of superior canal dehiscence, including:
- Developmental abnormality of the bone over the semicircular canal
- Thinning bone associated with aging and/or vascular changes
- Head trauma
- Complication during surgery of the ear
You have a greater chance of getting superior canal dehiscence if you have a thin bone over the semicircular canals, predisposing you to a dehiscense following a mild head injury, barotrauma, or increased intracranial pressure such as with strained physical exertion or excessive sneezing.
Most cases of SCD occur in only one ear, but can affect both ears simultaneously.
What are the symptoms?
The most common symptom of superior canal dehiscence is vertigo, which can be elicited by loud noises (Tullio’s phenomenon) or an increase in intracranial pressure such as when sneezing, coughing, or physical straining. Symptoms of vertigo will usually increase with activity and decrease during rest.
Other symptoms of superior canal dehiscence can include a hypersensitivity to sounds, especially one’s own voice (autophony) in which the voice is described as “boomy”. Some people may also experience a hearing loss, fullness, and tinnitus in the affected ear.
How is superior canal dehiscence diagnosed?
Superior canal dehisence is most commonly diagnosed with the use of a high resolution CT scan of the temporal bone, which will show the missing or thinned bone.
Other tests that may be performed to help diagnose SCD include:
- Vestibular evoked myogenic potential (VEMP) test
- MRI scan
- Comprehensive audiologic evaluation
- Valsalva test
- Fistula test
- Tympanometry test
- Vestibulonystagmography (VNG) test
Many of these tests are done while observing and/or recording eye movements (nystagmus), as the eye movements will indiate whether an inner ear vestibular response was elicited.
The signs and symptoms of SCD can sometimes mimic other disorders of the ear, such as otosclerosis, Meniere’s Disease, BPPV, and perilymph fistula. For this reason, it is important that a comprehensive evaluation of ear function be performed before diagnosis is made. An Otolaryngologist and/or Otologist will likely recommend the appropriate tests be performed by an Audiologist in addition to imaging scans. Diagnosis should never be made based on the results of one of the above tests alone.
How is it treated?
Unfortunately, superior canal dehiscence is not likely to resolve on it’s own. There are two options when it comes to treating superior canal dehiscence: the conservative approach of adjusting one’s lifestyle to avoid things that cause the symptoms, or surgery to correct the dehiscence.
The conservative approach involves avoiding things that cause the vertigo, such as physical straining or lifting, nose blowing, activities of pressure change such as flying or diving, and loud noises.
Surgical treatment of superior canal dehiscence involves plugging or capping the dehiscence of the bone.
Does superior canal dehiscence cause lasting problems?
The severity of SCD will vary from person to person. For mild cases, an understanding and avoidance of the provoking activities and stimuli is enough. For more severe cases, SCD can cause a debilitating chronic imbalance or vertigo, as well a significant hearing loss and/or sensitivity to sound stimuli.