Which finding best characterizes superior canal dehiscence?

• A. Thinned bone over the superior semicircular canal causing vertigo or disequilibrium with loud noises (Tullio phenomenon) or pressure changes; low-frequency VOR abnormalities.
• B. Progressive unilateral SNHL.
• C. Normal caloric testing with no nystagmus.
• D. Hearing loss only with high-frequency sounds.

Answer: (A)

Superior canal dehiscence creates a third window in the inner ear because the bone over the superior semicircular canal is thinned or missing. This abnormal window alters the vibration mechanics of the vestibular system, so sounds or pressure changes can provoke vertigo and disequilibrium. That’s why vertigo can be triggered by loud sounds (the Tullio phenomenon) or by changes in pressure, and you often see low-frequency vestibulo-ocular reflex abnormalities, while higher-frequency responses may be less affected.

Understanding this helps distinguish it from other patterns: progressive unilateral sensorineural hearing loss points to cochlear hair cell loss or neural issues rather than a vestibular third window; normal caloric testing would not explain the provocative vertigo with sound/pressure; and hearing loss limited to high frequencies is more typical of cochlear pathology, not a third-window syndrome.