Semicircular Canal Dehiscence (SSCD) is a disease caused by the communication of the structures within the inner ear. Healthy individuals have 2 holes or "mobile windows" in their dense otic capsule bone, but those with SSCD have developed a third hole. The thinning or absence of bone located in the semicircular canal triggers vertigo, hearing loss, disequilibrium, and other vestibular and auditory symptoms. A common clinical symptom of SSCD reported by patients is the abnormal amplification of internal body sounds such as heartbeats and eye movement.
SSCD is considered a rare disease and the exact cause is unknown. A study by Carey et al.  analyzed 596 random cadavers of asymptomatic subjects and found an incidence of 0.7%. Most individuals do not present with any clinical symptoms until they reach middle age, although it has been seen in small children.
There are a variety of auditory tests that physicians use to detect and evaluate SSCD including computed tomography and vestibular evoked myogenic potentials. Although these tests are commonly used, routine assessments are not beneficial in the discovery of existing abnormalities.
High-resolution computed tomography (CT) scans of the temporal bone is crucial for physicians to diagnose, confirm, and locate SSCD. Sometimes CT scans can overestimate the SSCD when the size is below 3 mm. Thus, it is important to conduct other clinical and neurophysiological tests to compliment the radiological findings.
Vestibular-Evoked Myogenic Potential (VEMP) responses are used by physicians to confirm a suspected presence of SSCD. Patients with SSCD typically have a lower threshold for VEMP response elicitation and larger VEMP amplitudes. VEMP is also important is determining if it is SSCD that is causing conductive hearing loss instead of a true ossicular disease. Patients with a true ossicular disease have test results that are either absent or of elevated thresholds.
For patients with mild to no symptoms, it is best to be conservative and simply avoid symptom triggers. Patients with primarily pressure-induced symptoms can have a tympanostomy tube placed, but its efficacy is highly variable. Patients who present with clinical manifestations can also be surgically treated.
The transmastoid approach and the middle fossa craniotomy are the two main methods of surgical management where the surgeon resurfaces, plugs, or caps the bony dehiscence. Using the middle fossa craniotomy allows the surgeon to directly visualize the bony dehiscence and has been reported to effectively alleviate vestibular issues. Although the dehiscence cannot be visualized through the transmastoid approach, it offers a slightly lower risk of cerebrospinal fluid leak and intracranial complications. Dehiscences can be resurfaced only through the middle fossa craniotomy while plugging can use either approach. However, using the transmastoid approach to plug increases the risk of harming vestibular and cochlear structures, which results in a higher risk of hearing loss. Middle fossa craniotomy resurfacing also has a slightly higher risk of seizure than the transmastoid approach because the temporal lobe needs to be retracted. There are always risks associated with surgery, but most patients report a high level of improvement after surgical treatment.
A video segment on the Doctors featuring one of the prominent UCLA SSCD Surgeons, Dr. Isaac Yang, can be seen here: http://home.btconnect.com/tjs1/SCDS/SCDS.mp4
A video on the surgical treatment can be seen here: http://vimeo.com/39009411
For recent updates on the disease, visit: https://www.facebook.com/SuperiorSemicircularCanalDehiscence
Read a patients journey through her treatment of SSCD:
More information on SSCD can be found here: http://www.dizziness-and-balance.com/disorders/unilat/scd.htm
1. Carey, J.P., L.B. Minor, and G.T. Nager, Dehiscence or thinning of bone overlying the superior semicircular canal in a temporal bone survey. Archives of otolaryngology--head & neck surgery, 2000. 126(2): p. 137-47.
Isaac Yang, M.D.
Isaac Yang, M.D.
Quinton Gopen, M.D.
Quinton Gopen, M.D.