A case report of superior semicircular canal dehiscence syndrome

The superior semicircular canal dehiscence (SSCD) syndrome was first reported by Minor et al. in 1998. They reported that patients with SSCD typically exhibit symptoms of oscillopsia and pressure-/sound-induced vertigo due to the absence of the bony layer covering the superior semicircular canal. Although many cases of SSCD have been reported from America and Europe, only fourteen cases have been reported in Japan since 2003. We report a case of SSCD. The patient was a 30-year-old man who presented with the complaint of unsteadiness. He had been administered streptomycin for the treatment of pulmonary tuberculosis when he was 12 years old. Pure-tone audiometry showed a sloping pattern of sensorineural hearing loss bilaterally, with detection of 40 to 55 dB at high frequencies. Rightward-beating nystagmus was observed when the patient lay down, but not when he was sitting. Caloric responses were normal, ruling out the effect of streptomycin. Coronal computed tomography with 1.0-mm collimation revealed dehiscence of the left superior semicircular canal. Fistula symptoms were observed when positive pressure was applied to the external auditory canal. Tullio's phenomenon was also observed with sound stimulation (100 dB, 5Hz, click sound) to the left ear. These findings were compatible with the features of SSCD. The body-position dependency of the rightward-beating nystagmus could be attributable to changes in the intracranial pressure or intralabyrinthine pressure with the body posture, or to the nystagmus being of the pulse-synchronous type. A sloping pattern of the sensorineural hearing loss may be one of the characteristics of SSCD.