Use of high resolution thin section CT scanning of the petrous bone in temporal bone anomalies.

High resolution thin section axial CT scans (REVIEW reconstruction ARRANGE reformation--General Electric copyright were utilized to evaluate the petrous bone of 17 patients, ages 3 to 60, with congenital hearing loss. Two scanning protocols were evaluated: 1.5 mm thick sections at 1.5 mm intervals, and 1.5 mm thick sections at 1.0 mm intervals. These protocols were qualitatively compared with regard to 1. visualization of small anatomical structures, and 2. computer reformatted images in coronal and sagittal planes. Our experience suggests this imaging capability is highly useful in th evaluation of congenital ear abnormalities. Seventeen patients were examined with high resolution CT scans. The inner ear abnormalities included varying degrees of Mondini's dysplasia. The large vestibule, the large fenestra into the internal auditory canal, as well as the poor cochlear formation, were seen in these malformations. These studies have allowed a greater degree of accuracy in counseling parents of patients with inner ear malformations. Middle and external ear deformities were also encountered. The imaging technique is capable of demonstrating ossicular deformities, as well as the nature of canal atresias. It is particularly useful in the planning of surgery on some of these patients in that location of the plane of the facial nerve canal can be determined prior to surgery. This provides the ability to determine whether surgery is possible, and if so, the probability of opening the middle ear adequately to obtain appropriate reconstruction. Illustrative cases demonstrate the ease of visualizing the small structures of the inner and middle ear and the ability to review these structures in any plane utilizing the ARRANGE program.