Anatomo-radiological study of the superior semicircular canal dehiscence of 37 cadaver temporal bones.

ABSTRACT

PURPOSE: To assess the presence of dehiscence of the superior semicircular canal (SSCC) on computed tomography (CT) scanning and to study the microscopic anatomo-radiological correlation. MATERIALS AND METHODS: Thirty-seven temporal bones preserved in formalin, regardless of the clinical history of cadavers, were studied. A microscopic anatomical study was conducted with an operative microscope (20×). The settings of the CT permitted to obtain 0.6 mm slices contiguous reconstruction in Pöschl plane and in Stenvers plane. Three-dimensional (3D) reconstructions were performed if a radiological dehiscence was observed. The apex thickness was measured in Pöschl plane. The radiological positive criterion of SSCC dehiscence was an absence of bone coverage of more than 1 mm long in Pöschl and Stenvers planes. RESULTS: We observed three dehiscences of the 37 temporal bones on CT in Pöschl and Stenvers planes. However, no dehiscence was found microscopically. The 3D reconstruction was also positive in these three cases. Reconstructions in the Pöschl plane offered good results up to a bone thickness of 0.6 mm. When it was lower than 0.6 mm, the interpretation of the images appeared to be subjective. CONCLUSION: This study emphasizes the limitations of CT imaging, with a risk of false positives to take into account when interpreting the images. The 3D reconstructions also give too many false positives to be used alone and make an accurate diagnosis. The diagnosis of SSCC dehiscence will therefore remain clinical. Complementary and instrumental radiological examinations should be performed only to confirm this clinical suspicion.