Dimensional measurements of inner ear structures by CT target imaging

We investigated the clinical value of CT target imaging with 1.5mm slice thickness for the purpose of finding out the bony inner ear anomalies. In this communication, we have reported the results of dimensional measurements of inner ear structures in 30 ears with normal hearing and described five cases of inner ear anomalies which were found by CT target imaging. The diameter of the porus of internal auditory canal is about 1.0mm bigger in anteroposterior plane (6.71mm) than in vertical plane (5.70mm). The length of the internal auditory canal is very variable in individual cases in both axial and coronal projections compared with the other parameters of inner ear structures. The long axis of bony vestibule (6.49mm) is about 2.3 times large compared with the short axis (2.83mm) in axial projection. The obtained diameter of the short axis of bony vestibule (2.83mm) in axial projection is about the same as the diameter of the transveres axis (2.93mm) in coronal projection. The obtained diameter from the inner wall of the vestibule to the most lateral part of the lateral semicircular canal is about the same in both axial projection (4.82mm) and coronal projection (4.47mm). The distance between the lateral semicircular canal and the posterior semicircular canal in axial projection is about 2.40mm. When the obtained values of dimensional measurements of inner ear structures were compared between the ears with normal hearing and ears with sensorineural hearing loss, the CT target imaging with 1.5mm slice thickness seems to be very useful for finding out the inner ear anomaly which is one cause of the sensorineural hearing loss of unknown etiology. (J.P.N.)