High resolution computed tomography in stapedial otosclerosis

The value of high-resolution CT scanning in diagnosing stapedial otosclerosis and in influencing surgical planning was studied. 40 cases, consisting of patients of both genders, above the age of 14 years, with a clinical diagnosis of otosclerosis underwent HRCT of the temporal bones. Images were acquired in axial plane, with a bone algorithm, keeping slice thickness at 0.5 mm and intervals of 0.5 mm. Reconstruction of the volume data set was done to obtain overlapping slices in various planes, so as to obtain the best possible images of the footplate of stapes. The thickness of the footplate was measured and the site of lesion was noted in these images. On exploratory tympanotomy, the footplate was assessed and graded according to a visual scale. HRCT was able to diagnose stapedial otosclerosis in 85% ears. It was able to identify the presence of a thickened footplate correctly with a sensitivity of 85.3% (P value 0.16). It was able to correctly localize the site of otosclerotic focus in 85% cases (P value <0.01). Thus, an estimate of the thickness of the footplate likely to be encountered and thus the amount of drilling likely to be required to create a fenestra; and the likely site of maximum thickness could be made pre-operatively. This study also established the value of multislice CT on the acquisition of such data. This method obviates the requirement of difficult patient positioning, reduces scanning time; while greatly improving the sensitivity of the scanning.