Incidence of semicircular canal dehiscence in Singapore.

Semicircular canal dehiscence is a congenital syndrome that mainly affects the superior and, less commonly, the posterior semicircular canals. The diagnosis of superior semicircular canal dehiscence syndrome depends on the demonstration of a very small defect in the bony wall of the superior semicircular canal. Any amount of intact bone present excludes the diagnosis. The study will give an approximation of the incidence of semicircular canal dehiscence in Singapore. No specific data regarding the number of such cases exist currently. Retrospective review of CT scans of the temporal bone performed at our institution between January 2005 and July 2007 revealed a total of 10 such cases over this period, comprising 8 males and 2 females, with all cases involving the superior semicircular canal. Almost all of the patients scanned had evidence of previous or existing cholesteatoma. Three patients had bilateral superior semicircular canal dehiscence (all males), with an almost equal number of semicircular canal dehiscence on both sides for both sexes. Our study shows no significant advantage to obtaining reformatted oblique sagittal images for all temporal bone studies, unless the visualized walls show questionable defects. In these cases, reconstructed images are probably advantageous and should be obtained and reviewed.