Superior Canal Dehiscence Syndrome (SCDS)
Superior semicircular canal dehiscence is a condition in which there is a hole in the part of the inner ear that controls balance. For some people, this hole lets in sounds and changes in pressure that affect hearing and balance. When pressure transmission through the hole causes noticeable symptoms, this condition is called superior canal dehiscence syndrome (SCDS).
What You Need to Know
- The cause of the opening in the superior semicircular canal is unclear. Some research suggests it could be present at birth.
- Not everyone who has a bony opening in the superior semicircular canal will experience SCDS symptoms. And those without symptoms may not need treatment.
- SCDS may cause hearing distortion, balance issues, dizziness and other problems.
- Symptoms typically do not become worse over time but can be triggered or worsened by sudden change in pressure inside the skull, like from a strong sneeze.
- Ear specialists (otologists or neurotologists) evaluate and treat SCDS. In some cases, SCDS can be treated with surgery.
What is SCDS?
Superior canal dehiscence syndrome is a rare disorder that happens when there is an opening (hole) between the brain cavity and the superior semicircular canal in the inner ear. The hole is covered by the lining of the brain cavity (the dura) — fluid does not leak out, but this opening allows sound and pressure to enter and leave the inner ear in the wrong direction. This can lead to hearing and balance problems.
The inner ear is located deep inside the bone at the base of the skull. It includes the cochlea, which helps us hear, and the vestibular system, which helps us balance. The semicircular canals are part of the balance system and are made of three delicate, fluid-filled loops of bone (canals) that help us keep our balance and steady our vision when we move our heads. For the canals to work properly, the inner ear bone needs to be closed. There must be only two openings: one for sound to go into the inner ear (oval window) and one for sound to leave (round window).
When the wall of the superior canal is too thin or there is an opening, sound and pressure can get into and out of the inner ear, causing problems with hearing and balance.
What causes superior canal dehiscence syndrome?
No one is certain what causes SCDS. Some studies suggest it might be present at birth. The superior semicircular canal is the last part of the inner ear bone to develop in a fetus. If this process is not completed, it perhaps could lead to SCDS.
Sometimes, symptoms of SCDS start suddenly after an injury to the head or another event that causes a sudden pressure wave inside the skull. Research shows that SCDS could develop over time due to thinning of the bone of the superior semicircular canal. This thinning may be caused by pulsing of the dura onto the thin bone over the canal.
Superior Canal Dehiscence Syndrome: Q&A with a Johns Hopkins Expert
SCDS Symptoms — What to Look For
SCDS can affect one or both ears, and symptoms can be constant or come and go. However, for most people with SCDS, symptoms do not go away on their own. People who have SCDS may experience changes in hearing and balance.
Hearing Distortions and Autophony
For people with SCDS, certain sounds from within their body may be abnormally loud in the affected ear. They may hear their voice, pulse, stomach or digestive noises, or even eyeballs moving very loudly. This is called “autophony.” People often use this term to describe hearing their own voice loudly. Autophony is caused by the opening in the superior semicircular canal, which allows sounds from various parts of the body to enter the inner ear.
Balance Problems and Dizziness
SCDS affects the normal ability of the superior semicircular canal to detect head movements. This can make a person feel dizzy or unsteady, or have a sense of motion when they are exposed to loud noises or changes in pressure inside the skull. This can happen during sneezing, straining and coughing, which create pressure changes in the skull.
The sound pressure from loud sounds can also cause abnormal movements in the fluid in the inner ear. Normally, the fluid only moves as a response to head movement. However, with an opening in the superior canal, the moving fluid in the semicircular canal can be perceived by your brain as sudden movements, leading to feelings of dizziness and imbalance.
Other Symptoms
In addition to the main symptoms of SCDS, people may experience problems including:
- Muffled hearing
- Feeling like the ears are full or plugged
- Trouble with the neck or shoulders from trying to keep the head upright
- Feeling that surroundings are moving, bouncing or going up and down in sync with the heartbeat
- Trouble thinking clearly, making decisions or remembering things — this “brain fog” is thought to be caused by the extra effort and focus it takes to hear people talk, to communicate and to stay balanced while trying to figure out the mixed signals from the balance system (all of this is very tiring and fatigue is common)
Diagnosing Superior Canal Dehiscence Syndrome
If a doctor thinks you might have SCDS, the doctor will likely do the following to narrow down the diagnosis:
- Ask you about your medical history and examine you, focusing on the ears, eye movements and balance
- Look at the bones of the head with a specialized computerized tomography (CT) scan of the bone around the ear, which can show if there is a hole in the bone of the superior semicircular canal
- Check your hearing with a test called an audiogram
- Perform other tests to evaluate the balance system
Other Conditions to Consider
SCDS can be hard to diagnose because it is rare, some symptoms are difficult to describe and other health issues can cause similar symptoms. Your doctor may conduct more tests. Other health problems that may share symptoms with SCDS include:
- Vestibular migraine
- Eustachian tube dysfunction
- Pseudotumor cerebri (also called idiopathic intracranial hypertension)
Treatment for Superior Canal Dehiscence Syndrome
- People who have a hole in the superior canal, confirmed by a CT scan, but do not have any symptoms may not need treatment.
- People who have symptoms of SCDS that are bothersome should see an ear specialist, who can help diagnose the problem and suggest treatments. Simple ways to manage SCDS symptoms include avoiding loud noises and activities that cause straining, like heavy lifting. Your doctor may also recommend vestibular therapy.
- For people whose symptoms are severe and affect daily life, surgery may be an option. This type of surgery can plug the hole in the superior canal and relieve many symptoms.
An ear specialist can help you determine if you have SCDS and what treatment may be best for you.
Superior Canal Dehiscence Syndrome – Getting a Correct Diagnosis
Johns Hopkins Otology and Neurotology
The Johns Hopkins Otology, Neurotology and Skull Base Surgery team is dedicated to diagnosing and treating superior canal dehiscence, acoustic neuromas, and other conditions of the skull base.
