First Described in 1998, by Dr Lloyd Minor, Superior Canal Dehiscence is a condition where there is a segment of bone missing from the roof of the Superior Semicircular Canal which increases the compliance of the inner ear. Approximately 2% of the population have superior canal dehiscence.
With the transmission of sound, the stapes bone in the middle ear vibrates, conducting pressure pulses in the fluid of the inner ear that causes the sensitive hair cells in the cochlea and balance organ to detect hearing and movement. Normally there are only 2 “windows” into the inner ear: the oval window which is where the stapes sits and vibrates in the inner ear and the round “window” which is at the base of the cochlea where this pressure can dissipate.
However with bone missing on the roof of the superior canal, it creates a third window in the inner ear which is abnormal. This creates an abnormal movement of fluid in the inner ear, thus causing a sensation of vertigo with sound, especially when it is loud, as it causes more vibration of the stapes into the inner ear. It also causes vertigo with pressure transmitted from the brain to the inner ear, such as when straining or blowing one’s nose.
The condition may also be associated with the appearance of conductive hearing loss on the audiogram. This is usually not a true hearing loss and instead people often complain of hypersensitivity to sound rather than hearing loss.
Surgical treatment may be required and although there are a few techniques available, most commonly involves covering or plugging the superior canal so fluid cannot pass through it.