Superior Canal Dehiscence Syndrome (SCDS)
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. The condition causes problems with hearing and balance.
- SCDS is a rare condition caused by an abnormal thinness or incomplete closure of one of the bony canals in the inner ear.
- The problem can cause hearing loss, sound distortion and balance problems triggered by loud noises or intracranial pressure caused by sneezing or coughing.
- Patients often hear internal sounds — their voice, pulse, chewing, eyes moving — or their footsteps in the affected ear.
- Symptoms may appear spontaneously or after a trauma or other incident that breaks the abnormally fragile canal.
- SCDS warrants a visit to a specialist who can assess this unusual disorder, and, if necessary, treat it with surgery.
What causes superior canal dehiscence?
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.
Symptoms of Superior Canal Dehiscence Syndrome
SCDS 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 disturbing symptom of SCDS is autophony (“hearing one’s 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 SCDS speak, they may hear their voice simultaneously from inside and outside of the body, which can be overwhelmingly loud. Many patients with SCDS resort to whispering.
Superior Canal Dehiscence Syndrome (SCDS): Diagnosis and Treatment
A specialist may be able to detect SCDS by using a computed tomography (CT) scan, but CT may give a false impression of a dehiscence when the bone is simply thin but intact. Hearing tests are critical to the proper diagnosis, as is an exam by a neurotologist. Another diagnostic test, called vestibular evoked myogenic potential (VEMP), should also be used — a sound generator tests reactions in neck muscles or eye muscles.
Surgery to correct the dehiscence can bring relief for those who are debilitated by their symptoms. The surgeon creates an opening (craniotomy) in a part of the skull called the middle fossa to gain access to the inner ear. An approach through the mastoid may also be an option in some cases. Surgery may involve image guidance.
The surgeon plugs the canal to eliminate most of the fluid movement, and may resurface the canal. When patients are properly selected for this surgery, they generally do very well and find relief of their hearing and balance symptoms.
Reviewed by John Carey, M.D., from the Department of Otolaryngology-Head and Neck Surgery