A gap or thinning in the bone covering the top of the superior semicircular canal. Causes vertigo and hearing changes triggered by loud sounds, physical straining, or pressure changes — a rare but often misdiagnosed condition.
Medical definition
Superior canal dehiscence syndrome (SCDS), first described by Lloyd Minor in 1998, results from a defect in the bone of the arcuate eminence — the ridge of temporal bone that covers the superior semicircular canal. This dehiscence creates an abnormal third mobile window into the inner ear (in addition to the oval and round windows). Sound energy and pressure changes that should drive fluid movement in the cochlea instead leak through the dehiscence, stimulating the superior canal and producing vertigo. The characteristic features are: vertigo or oscillopsia triggered by loud sounds (Tullio phenomenon), vertigo with straining or pressure changes (Valsalva-induced), autophony (hearing one’s own voice or body sounds loudly), low-frequency bone conduction hearing better than normal on audiometry, and a visible bony gap on high-resolution CT of the temporal bone.
Why it matters for vertigo
SCDS is frequently misdiagnosed because clinicians are not familiar with its characteristic combination of sound-triggered vertigo and autophony. Patients are often labelled with Meniere’s disease, perilymph fistula, or anxiety for years before the correct diagnosis is made. The audiometric finding is distinctive and free: bone conduction thresholds that are better than 0 dB HL at low frequencies — air-bone gaps without middle ear pathology — should always prompt a temporal bone CT. CT findings (a visible thinning or gap in the bone over the superior canal) confirm the diagnosis. Management ranges from observation and avoidance triggers to surgical canal plugging or resurfacing for severe cases.
Where I see this in clinic
I think of superior canal dehiscence when a patient describes vertigo that happens specifically when they hear a loud noise — a truck horn, a loud speaker, their own singing voice — or when they strain on the toilet or blow their nose. These triggers are not typical of BPPV, Meniere’s, or vestibular neuritis. In online second-opinion consultations, I ask directly about autophony (does your voice sound abnormally loud in your head?) and about sound-triggered spinning. When both are present alongside normal MRI and normal standard audiometry, I request a temporal bone CT and cervical VEMP testing, and refer for a specialist otologist opinion if CT confirms the diagnosis.
Related terms
Oscillopsia – can be triggered by sound in superior canal dehiscence. Aural fullness – sometimes present, which can mimic Meniere’s disease. Caloric test – may show superior canal abnormality in some cases. Nystagmus – vertical-torsional nystagmus is triggered by loud sounds in active SCDS.
Medical Disclaimer: This glossary entry is for educational purposes only. Consult Dr. Prateek Porwal directly. WhatsApp: 7393062200.