Superior Canal Dehiscence Syndrome

Superior Canal Dehiscence Syndrome (SCDS) is caused by an abnormal opening between the uppermost semicircular canal in the upper part of the inner ear and the brain.

Deep inside the inner ear are three delicate, fluid-filled loops called semicircular canals, which detect head rotations. In very rare instances, during fetal development, the uppermost semicircular canal fails to close or thicken normally. Both normal balance and hearing depend on this canal forming a closed passageway, with sound coming in through one end (the stapes bone at the oval window) and out the other (an opening in the inner ear called the round window). With a thin area or opening in the canal, sound can “leak” through and reverberate in the brain. In addition, the vibration of sound can move the fluid in the canal.

Superior Canal Dehiscence Syndrome can cause problems with hearing and balance, either intermittent or constant. Sound vibrations escape the normally closed system of the inner ear and activate the hair cells that sense rotation in the superior canal. A loud noise can cause a sensation that the world is tumbling or bobbing up and down. Coughing or sneezing can cause the same phenomenon.

Another somewhat disturbing symptom of Superior Canal Dehiscence Syndrome is autophony ('hearing one self'). While some sounds from the outside of the body are perceived normally through the ear, sound from inside the body such as breathing, heartbeat and blood flow — or even slight movement of the muscles surrounding the eye — may enter the inner ear directly through the abnormal third opening.

When people with Superior Canal Dehiscence Syndrome speak, they may hear their voice simultaneously from inside and outside of the body, which can be overwhelmingly loud. Many patients with Superior Canal Dehiscence Syndrome resort to whispering to avoid hearing too much noise.