Semicircular Canal Dehiscence Syndrome (SSCDS)
Symptoms of vertigo (spinning dizziness or sense of movement) caused by loud noises or changes in middle or inner ear pressure has been recently discovered in patients with a defect (dehiscence) in the bone covering the semicircular canal of balance in the inner ear. Such patients may also have chronic dizziness. The boney defect in the semicircular canal allows for abnormal movement of the inner ear membranes in the superior semicircular canal to respond inappropriately to sound or pressure changes in middle ear or head pressure to activate the nerve endings of balance leading to the symptoms of vertigo. Normally the intact boney canal prevents abnormal displacement of the semicircular canal inner ear membranes and fluid, when subjected to sound or pressure changes. Activities such as pushing on the outer ear, use of Q-tips, coughing, hiccupping, nose blowing, sneezing riding in an elevator in a tall building, or straining can cause these pressure changes. Echoing of one’s own voice (autphony) may occur in some patients with SSCDS.
In the adult the boney dehiscence of the semicircular canal is caused by erosion the thin bone partition separating the brain cavity from the base of the skull containing the semicircular canals. Such erosion can occur from pressure from the brain pulsations and its surrounding membrane (the "dura"). The superior semicircular canal, closest to the overlying brain and dura, is the most commonly affected canal associated with this syndrome.
Patients with SSCDS may initially present with unusual symptoms of a bobbing of their vision or the panorama (oscillopsia) in association with their pulse, walking, or pressure changes. They may complain that they "hear" their eyes moving. They may also have a low frequency conductive hearing loss, which may be confused with otosclerosis form of conductive hearing loss.
Diagnosis of SSCDS
A diagnosis of SSCDS can be considered with characteristic symptoms, and certain observed eye movements (nystagmus) elicited with sound or pressure stimuli. These eye movements can be directly visualized by your examiner or with video recordings. A "vibration" test is frequently performed to elicit characteristic brisk rotational eye movements (torsional nystagmus) with a hand-held vibrator applied to the back of the head.
In addition to initial audiometric (hearing) test, ancillary diagnostic tests have been utilized, such as vestibular evoked myogenic potentials (VEMP) elicited by loud tones to cause reflex responses in certain neck muscles. One of the inner ear balance end organs (sacculus) is stimulated by the loud sound to produce a reflex activity recorded from the activated neck muscle
The most definitive test for SSCDS is with high resolution CT scan imaging to demonstrate the opening of the bone lining the semicircular canal. The CT scan is specially formatted also not to miss thin but intact bone covering the semicircular canal.
Management of SSCDS
After an accurate diagnosis is made, which is sometimes difficult because SSCDS may be seen in varying combination with other disorders affecting the inner ear or nervous system. In the past perilymphatic fistula has been unsuccessfully treated for these symptoms of vertigo and hearing loss. Some patients may be able to minimize or control their symptoms by avoiding the sounds or activities that produce the vestibular disturbances. Such activities can be: pushing on the outer ear, use of Q-tips, coughing, hiccupping, nose blowing, sneezing riding in an elevator in a tall building, scuba diving, or straining Those with debilitating symptoms may require surgery to repair the dehiscent semicircular canal with bone wax or graft through the mastoid or middle cranial fossa approach.