The main purpose of this study is to determine the radiological incidence of Superior (SSCD) and Posterior Semicircular Canal Dehiscence (PSCD) and to compare radiologic SSCD to the incidence of this condition on cadaver specimen. We have also analysed the relation between the ossification state of the semicircular canals and the degree of mastoid pneumatization and integrity of Tegmen Tympani.Temporal bones have been investigated by means of CT scan on patients and direct observation on cadaver specimen, respectively.604 ears and 160 cadaver temporal bones have been investigated by means of CT scan and direct observation, respectively. 3.6% and 0.3% of the studied ears had SSCD and PSCD, respectively, on CT scan. Only 0.6% of the cadaver specimen ears did have anatomical SSCD. Degree of pneumatization of the mastoid bone is related to the mean thickness of bone overlying the Superior and Posterior Semicircular Canal. Radiological absence of Tegmen Tympani is more frequent in ears that also have radiologic SSCD.CT scanning gives higher incidence figures of SSCD than anatomical studies, 3.6% vs. 0.6%. We also found a 0.6% incidence of radiological PSCD in the studied ears. There is a direct relation between the degree of ossification of Superior and Posterior Semicircular Canal and certain temporal bone anatomic features: temporal bone pneumatization and absence/presence of Tegmen Tympani or Antri.