Superior semicircular canal dehiscence: prevalence in a population with clinical suspected otosclerosis-type hearing loss.

Superior semicircular canal dehiscence (SSCD) can present with a variety of symptoms that can be predominantly auditory, predominantly vestibular or both. It can mimic a wide range of otological disorders, in particular otosclerosis-like stapes fixation. Our study revealed that, in 5.3% of our patients with clinically suspected otosclerosis, SSCD was detected in high-resolution multi-detector computed tomography (HRMDCT) of the temporal bone. We therefore emphasise the value of HRMDCT with reconstructions in the plane of the superior semicircular canal and perpendicular to the superior semicircular canal in the diagnostic work-up of each patient with a tentative diagnosis of otosclerosis-type stapes fixation. Where there are doubts, VEMP testing should be performed. We believe that a number of unexplained complications after an uneventful stapedotomy procedure might be explained by a pre-operatively undetected dehiscent superior semicircular canal and therefore unwarranted surgery. The typical feature of the conductive hearing loss due to SSCD compared to otosclerosis is an air-bone gap which is much more prominent at low frequencies than at high frequencies.