SUPERIOR SEMICIRCULAR CANAL DEHISCENCE SYNDROME : A BRIEF

Superior semicircular canal dehiscence syndrome is a set of hearing and balance symptoms, related to a rare medical condition of the inner ear, known as superior canal dehiscence. The symptoms are caused by a thinning or complete absence of the part of the temporal bone overlying the superior semicircular canal of the vestibular system. There is evidence that this rare defect, or susceptibility, is congenital. There are also numerous cases of symptoms arising after physical trauma to the head.

Symptoms of SCDS include:

• Autophony – person's own speech or other self-generated noises (e.g. heartbeat, eye movements, creaking joints, chewing) are heard unusually loudly in the affected ear
• Dizziness/ vertigo/ chronic disequilibrium caused by the dysfunction of the superior semicircular canal
• Tullio phenomenon – sound-induced vertigo, disequilibrium or dizziness, nystagmus and oscillopsia
• Pulse-synchronous oscillopsia
• Hyperacusis – the over-sensitivity to sound
• Low-frequency conductive hearing loss
• A feeling of fullness in the affected ear
• Pulsatile tinnitus

DIAGNOSIS

The presence of dehiscence can be detected by a high definition (0.6 mm or less) coronal CT scan of the temporal bone, currently the most reliable way to distinguish between superior canal dehiscence syndrome (SCDS) and other conditions of the inner ear involving similar symptoms such as Ménière's disease, perilymphatic fistula and cochlea-facial nerve dehiscence.[8][9] Other diagnostic tools include the vestibular evoked myogenic potential or VEMP test, videonystagmography (VNG), electrocochleography (ECOG) and the rotational chair test. An accurate diagnosis is of great significance as unnecessary exploratory middle ear surgery may thus be avoided. Several of the symptoms typical to SCDS (e.g. vertigo and Tullio) may also be present singly or as part of Ménière's disease, sometimes causing the one illness to be confused with the other. There are reported cases of patients being affected by both Ménière's disease and SCDS concurrently.

TREATMENT

Once diagnosed, the gap in the temporal bone can be repaired by surgical resurfacing of the affected bone or plugging of the superior semicircular canal.These techniques are performed by accessing the site of the dehiscence either via a middle fossa craniotomy or via a canal drilled through the transmastoid bone behind the affected ear. Bone cement has been the material most often used, in spite of its tendency to slippage and resorption, and a consequent high failure rate; recently, soft tissue grafts have been substituted