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Semicircular Canal Dehiscience

Superior Canal Dehiscence Syndrome

For over 100 years ear specialists have recognised that, in certain conditions, the sound transmitted to the inner ear may activate the vestibular (balance) system. The inner ear consists of a cochlea (hearing component) and fluid-filled canals (balance component). These normally work independently, however, patients with some conditions or diseases have reported that sounds can cause vertigo (spinning sensations) and nystagmus (eye movements). It is assumed that the sound causes fluid in the balance canals to move, which gives the person the impression that they are physically moving. This can be a minor and temporary inconvenience or a major disability. In many cases the imbalance disappears when the underlying condition is addressed.

A new condition was discovered in the 1990's, which could not be explained by any known disease or condition. Patients exhibited one or some of the following:

  • Imbalance
  • Hearing loss
  • High sensitivity or intolerance to sounds of certain frequencies or character (e.g. a mobile phone dial tone, a cry of a child, a particular note on a church organ)
  • Motion Intolerance
  • An ability to hear internal sounds such as eye movements or walking

X-ray and CT scans revealed that these people had a dehiscence (thinning) of the bone overlying one of the balance canals - the superior semicircular canal.

Sound normally moves the fluid in the cochlea which activates the hair cells and converts the sound into electrical signals. This same fluid is shared by the balance canals. Loud sounds change the pressure of the fluid in the cochlea and the canals. This may result in slight movement of the thinned bone, which is interpreted by the brain as physical movement. If the patient's eyes are open, visual cues tell the brain that there is no movement. This 'confusion' results in feelings of imbalance. The patient's eyes may also move suddenly in an effort to compensate for this apparent motion.

The cause of the condition is not fully understood. There appears to be a physical disposition to this condition, which is triggered by a particular event. It can occur in one or both sides of the head.

Diagnosis

Diagnosis involves a number of investigations, including a comprehensive hearing test, tests in a vestibular clinic to assess eye movement, and a CT scan. The direction of eye movement helps to determine if the problem is on the left or right side. The thinning bone can be seen on the CT scans.

Treatment

Patients seen by specialists at Ear Science Institute Australia have been successfully treated in one of two ways:

  • Diagnosis and counselling - a number of patients have been assisted merely by a diagnosis, which allows them to avoid the condition/s that trigger an attack. After many years of living with the condition they are relieved to have an explanation.
  • Surgery - surgery to repair the thinning of the bone has been very successful. This surgery must be performed under a general anaesthetic, and requires drilling through a section of the skull above the ear, and using a cement to thicken the covering over the superior canal. The problem is resolved for most patients, and significantly reduced for others.