Superior semicircular canal dehiscence syndrome (SSCDS) was first described in 1998 by Dr. Lloyd Minor, then of Johns Hopkins. Over the prior decades, otolaryngologists would encounter a patient who would be able to hear his or her own voice and internal body sounds (eye movements, heartbeat, tendon and ligament movements, etc) in usually one ear. In addition to this, the patient would often also get momentary episodes of dizziness when that ear was exposed to loud noise, with nose blowing, or with straining while having bowel movements. Often, these patients would be diagnosed with something called a perilymph fistula, where there is a leak of inner ear fluid from usually around the stapes bone (3rd hearing bone). But surgery to try to fix this would often not be beneficial to the patients.
It wasn’t until the resolution on CT scans became high enough that the anatomy of the superior semicircular canal could be better visualized. The superior semicircular canal is part of the peripheral vestibular (balance) system and helps to detect angular acceleration. It plays a role in keeping our eyes focused on something when our head does certain motions. Everyone is born with a certain thickness of bone over the superior semicircular canal. If someone is born with very thin bone over the superior semicircular canal, over time, as the brain rests on the skull base, that bone can wear away and eventually cause the inside of the superior semicircular canal to be in communication with the dura of the brain.
In certain patients, sound and pressure can be transmitted preferentially through this dehiscence. This can lead to an apparent conductive hearing loss, as sound is transferred through the dehiscence in the superior canal rather than into the cochlea. Sound and transmitted internal body pressure could also be transmitted through the dehiscence. With sound being more easily transmitted into the inner ear through the dehiscence, internal sounds can be heard in the affected ear. If intense enough, it can also deflect the cupula (a sense organ) of the superior canal, which can cause the patient to have momentary episodes of vertigo. And if pressure is transmitted through the dehiscence in the canal (such as with noseblowing), that can also deflect the cupula, also causing momentary episodes of vertigo.
Treatment of SSCDS
Medical therapy
What many neurotologists have found over the last 20 years regarding SSCDS is that there are many patients who have evidence of dehiscence on CT scans done for another reason, but no symptoms of SSCDS. In my opinion, the main reason why some patients have symptoms and some do not is because patients will have variable brain and nerve sensitivity. Therefore, the first treatment I usually offer patients, if they have not yet tried, is treatment for this sensitivity (a.k.a. treatment for migraine, even in the absence of headaches).
Information on migraine therapy can be found here:
https://briankungmd.com/migraine-associated-dizziness-migraine-in-otolaryngology/
There are patients who have symptoms and signs of SSCDS and are reassured that there is an explanation for their symptoms and choose to go the route of migraine therapy and hope to have improvement in the severity of their symptoms.
Surgical therapy
However, there is also surgery that can be done to treat SSCDS. The first approach is a transmastoid approach. This is an outpatient surgery where an incision is made behind the ear and the mastoid is opened with a drill. The semicircular canals are identified and the superior semicircular canal is outlined. Then a small opening can be made into each end of the superior canal and the lumen of the canal is plugged with fascia/perichondrium/bone dust and tissue sealant. The advantage of this approach is that it is usually done outpatient and is a more familiar approach for most ear surgeons. Also, it does not require the presence of a neurosurgeon in the vast majority of cases. The disadvantage of this approach is that the dehiscence is usually not directly visualized and sometimes, if the patient pushes in the region of the mastoid after surgery, he/she can have some symptoms. Therefore, the surgeon can choose to put a surgical mesh over the mastoidectomy defect to help prevent this problem postoperatively.
Another approach to treat SSCDS is middle fossa canal plugging. This is most often done in conjunction with a neurosurgeon. Sometimes, a lumbar drain is placed to help in elevating the dura off of the floor of the middle fossa where the dehiscent canal will be located. Patients will usually stay in the hospital at least overnight after this surgery. An incision is made from the ear up into the scalp. Bone is removed from the lateral aspect of the skull for later replacement. The dura is elevated off of the middle fossa floor and the dehiscence visualized. It is then plugged with fascia/perichondrium/bone dust and tissue sealant. The surgeon can choose to also consider resurfacing the middle fossa floor with bone cement. The dura is laid back down, the bone from the lateral aspect of the skull replaced, and the wound closed. The main advantage of this approach is that the dehiscence is directly visualized. The disadvantage of this approach is that it usually involves a hospital stay postoperatively. Some patients can also have some issues with swelling of the temporal lobe if it is elevated and retracted for long periods of time (relatively rare).
One of the biggest side effects of surgery is dizziness that hopefully will resolve in a few days. Patients usually will have resolution of at least the episodes of dizziness caused by loud noises and pressure changes within the body. They usually have reduction of the ability to hear internal sounds in the involved ear, but that symptom is not as reliably treated as the vestibular (balance) symptoms. Other risks can include loss of hearing in the ear, facial paralysis, loss of vestibular function, cerebrospinal fluid leak, recurrence of symptoms, and need for more procedures.
More information on SSCDS
https://entad.org/resources/patient-information-dr-teixido/superior-canal-dehiscence-syndrome/
Brian Kung, MD 