Superior semicircular canal dehiscence syndrome by the superior petrosal sinus

Thinning or dehiscence of the superior semicircular canal may occur on the middle cranial fossa floor or adjacent to the superior petrosal sinus (SPS). However, no symptomatic cases of superior canal dehiscence by SPS have been previously described. A 45-year-old woman presented with left-side pulsating tinnitus, autophony and disequilibrium. Examination showed conductive hearing loss and decreased threshold of vestibular evoked myogenic potential in the left side. Sound and vibration stimuli and positive pressure insufflations into the left ear evoked mainly torsional nystagmus instead of vertical-torsional nystagmus. High-resolution temporal bone CT revealed a dehiscence of the superior canal close to the common crus, which was encased by SPS. Symptoms and signs resolved after plugging the dehiscence through a middle fossa approach. Deep groove of SPS may cause superior canal dehiscence close to the common crus, and costimulation of the superior and posterior canals may explain the mainly torsional nystagmus induced by sound and vibration stimuli.