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Peripheral· Onset: Often gradual; sound/pressure-triggered · Duration: Chronic
Superior semicircular canal dehiscence (SSCD)
Overview
Summary
A bony defect in the roof of the superior (anterior) semicircular canal creates a 'third window' in the labyrinth, allowing sound and pressure to abnormally stimulate the canal and producing vertigo and conductive hyperacusis.
Diagnostic criteria
See the Bárány Society / clinical practice guideline papers[14,15] listed on the references page for the consensus diagnostic framework used in this profile.
Epidemiology
Radiographic prevalence ~1–2%; symptomatic dehiscence less common. Adults 30–50s.
Pathophysiology
Bone loss over the superior canal (developmental thinness + minor trauma) creates a third compliant window dissipating acoustic and pressure energy through the labyrinth.
Prognosis
Surgery resolves vestibular symptoms in most; small risk of hearing loss.
Key examination findings
- ◆Tullio phenomenon: vertigo + nystagmus evoked by loud sound (the nystagmus moves in the plane of the superior canal — vertical-torsional).
- ◆Hennebert sign: pressure-evoked vertigo (Valsalva, tragal pressure).
- ◆Autophony — hearing one's own voice, footsteps, eye movements amplified.
- ◆Conductive hyperacusis: hearing a tuning fork on the ankle.
Investigations
- ▸High-resolution temporal bone CT with reformatted images in Pöschl plane — gold standard.
- ▸VEMPs: lowered cervical VEMP thresholds and elevated ocular VEMP amplitudes on affected side.
- ▸Audiogram: 'pseudoconductive' hearing loss with supranormal bone conduction at low frequencies (negative bone-conduction thresholds).
Management
- ●Avoidance of triggers if mild.
- ●Surgical plugging or resurfacing of the dehiscent canal (middle fossa or transmastoid approaches) for disabling symptoms.
Clinical pearls
- ★Patient who reports hearing their eyes move or their footsteps loudly → think SSCD.
- ★VEMPs are very useful — both cervical and ocular.