Dehiscences of the semicircular canals as discrete third window lesions of the inner ear

The aim of this study was to assess the role of high resolution multi-detector CT in diagnosis of different dehiscences of the semicircular canals (SCC).Material and MethodsThis study was conducted on 20 patients within one year interval. All the patients had given clinical diagnosis of dehiscences of the SSC by clinical examination and/or audiogram. Sixty-four MDCT was used in assessment of all patients.ResultsCongenital defects of the SCC were encountered in 9 cases (45%); acquired defects were encountered in 11 cases (55%). Among the congenital defects, superior and posterior SCC were involved in 6 and 3 patients (30 and 15%) respectively. Congenital defects of lateral SSC were not encountered in this study. Cholesteatoma was the most common single etiology causing defect within the SCC.ConclusionRadiological diagnosis of SCC dehiscences depends on the use of high resolution MDCT. Ultrathin reconstruction with MPR is mostly sufficient in accurate display of the defects. Primary congenital dehiscences do occur in the superior SCC but also less commonly within the posterior canal. In this study, lateral canal dehiscence was only acquired. Secondary semicircular canal dehiscences could be caused by cholesteatoma and temporal bony aggressive mass lesions.