ABSTRACT
OBJECTIVE: To compare audio-vestibular findings caused by a dehiscence of the posterior semicircular canal with those found in the superior canal dehiscence syndrome. STUDY DESIGN: Case report. SETTING: University hospital, tertiary referral center. PATIENT: The 44-year-old woman suffered from a gradual hearing loss with pulse-synchronous tinnitus as well as sound and pressure-induced vertigo. INTERVENTION: Audio-vestibular testing and high-resolution computed tomography. MAIN OUTCOME MEASURE: The superior canal dehiscence syndrome is caused by failure of normal postnatal bone development in the middle cranial fossa leading to absence of bone at the most superior part of the superior semicircular canal. The typical features for this syndrome are sound- and pressure-induced vertigo with torsional eye movements, pulse synchronous tinnitus and apparent conductive hearing loss in spite of normal middle-ear function. We present a patient with very similar symptoms and findings who, instead, had a posterior semicircular canal dehiscence caused by an apex cholesteatoma. CONCLUSION: Patients with semicircular canal dehiscence have common auditory-vestibular features regardless of which of the two vertical semicircular canals is affected. The only obvious difference between the two is the vertical component of the sound and pressure-induced eye movements (which beats in opposite directions).