1Department of Otolaryngology, Seoul National University Bundang Hospital, Seongnam, South Korea/2Department of Neurology, Seoul National University Bundang Hospital, Seongnam, South Korea

■ OBJECTIVES: Superior semicircular canal dehiscence (SCD) syndrome is characterized by sound induced vertigo and conductive hearing loss due to the bony dehiscence of superior semicircular canal facing middle cranial fossa dura. Authors diagnosed and treated a case of SCD located unusual site by aberrant course of superior petrosal sinus, which presented atypical nystagmus.

■ METHODS: A 45 year old woman visited for left side pulsating tinnitus, autophony and disequilibrium. Diagnostic work up included high resolution temporal bone CT, temporal bone MRI, vestibular evoked myogenic potential (VEMP) and 3D video-oculography (stimulation: 500 Hz and 1 kHz tone burst, vibration, pressure).

■ RESULTS: Temporal bone CT showed encasement of left superior canal by aberrant course of superior petrosal sinus. The location was closer to common crus compared to usual SCD syndrome. Vibration and sound stimulation evoked purely torsional nystagmus. VEMP threshold of the left ear was lower by 20 dB than right ear. Pulsating tinnitus, autophony and disequilibrium were  esolved following separation of the sinus and surgical repair of the dehiscence via middle fossa approach.

■ CONCLUSIONS: Aberrant course of superior petrosal sinus can be the cause of SCD and induced nystagmus can be variable according to the location of the dehiscence.