Ear Center: Superior Semi-Circular Canal Dehiscence Syndrome
Superior Semi-Circular Canal Dehiscence Syndrome (SSCCDS)
Superior semi-circular canal dehiscence syndrome (SSCCDS) is a recently described condition in which there is an abnormal anatomic connection between the superior semi-circular canal (one of three semi-circular canals that are part of the inner ear balance mechanism) and the middle cranial fossa (the mid-portion of the inside floor of the skull) due to slow absorption of bone overlying the top of the canal. The absorption is probably secondary to constant pounding of the brain (dura) against the bone of the canal due to physiologic brain pulsations as well as variations in bone thickness among people. Usually seen in adults, it may develop as a result of congenital thinning of the normal bony partition between the balance system (vestibular system) and the base of the skull. Affected patients present with sound or pressure induced spinning dizziness (vertigo) and/or a perceived bouncing of the horizon during walking (oscillopsia) as well as a low frequency conductive hearing loss.
Superior semi-circular canal dehiscence and its surgical repair were first described by Lloyd Minor, M.D. and colleagues in 1998. Their report led to increasing awareness of the clinical disorder. The syndrome explained why some middle ears explored for otosclerosis (bone condition causing fixation of the third hearing bone, the stapes) had mobile stapes and "negative findings".
To date, several hundred patients, including many who suffered with symptoms for years, have been diagnosed and have undergone surgical repair that has resulted in hearing improvement and elimination of troublesome balance (vestibular) symptoms.
Definitive diagnosis of superior semi-circular canal dehiscence requires the use of high-resolution computed tomography
(CT scanning) of the skull bone that contains the ear (temporal bone) and physiologic testing with vestibular evoked myogenic potentials. However, recently, a new, in office screening vibration test has been introduced by Judith White, M.D., Ph.D. and colleagues in the Section of Vestibular and Balance Disorders of the Cleveland Clinic Head & Neck Institute.
Left ear: dehiscence of the left superior semi-circular canal (yellow arrow)
The vibration test is performed in the office setting and does not require any anesthesia. The test is performed by fitting patients with optical or video lenses (Frenzel lenses) that eliminate the ability to visually fixate. A hand-held, 100 Hz. vibrator is then applied to the back of the head near the lower hairline (posterior occiput). Patients with superior semi-circular canal dehiscence syndrome will respond with brisk rotational eye movements (torsional nystagmus). Patients with a positive vibration test then undergo CT scanning of their temporal bones and possibly vestibular evoked myogenic potentials
Like many other medical tests, the vibration screening test was discovered as a result of observations made during the treatment of patients who were thought to have another common balance disorder called "Benign Paroxysmal Positional Vertigo" or BPPV. When a vibrator was placed against their skulls in an attempt to treat their BPPV, patients with SSCCDS were noted to develop very unique and violent rapid eye motions (nystagmus). Further evaluation of such patients documented SSCCDS rather than BPPV.
As is common with most balance (vestibular) disorder, the patient's history is a key feature in suggesting the diagnosis of SSCCDS. Affected individuals will complain of dysequilibrium that is exacerbated by exposure to loud noises or to events that cause changes in middle ear and/or intracranial pressure, such as riding in an elevator in tall buildings, straining, hiccupping, or sneezing. Some patients may complain of their own voice echoing in their ear (autophony).
On audiometric testing, patients with SSCCDS will have nerve (bone) levels above 0 decibels. Although the same audiometric profile can be seen in patients with otosclerosis (autosomal dominant genetic hearing loss condition characterized by fixation of the stapes by abnormal hypervascular bone), otosclerosis patients have absent stapedial reflex tests (because their stapes are fixed) whereas patients with SSCCDS have normal acoustic reflexes (because their stapes are mobile, not fixed). Patients with SSCCDS have low frequency conductive hearing losses because they have three inner ear "windows" rather than the normal two "windows".
Once SSCCDS is diagnosed, definitive neurotologic or neurosurgical treatment requires bone graft repair of the dehiscent canal bone performed through a middle cranial fossa approach.
If you would like to learn more about the diagnosis and treatment of SSCCDS, please contact our office at (336) 273-9932.
- Copied and edited for clarification from: the Section of Vestibular and Balance Disorders of the Cleveland Clinic
Head & Neck Institute, 2006, page 5.
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Last revised October 21, 2012