Morphological characterization and classification of air cells in temporal bone by digital processing of CT images

Abstract

We determined the extent of pneumatization in the temporal bone and reconstructed three-dimensional structures of air cells by computer-assisted digital processing of high resolution CT images of the bone. We attempted morphological classification of temporal bone air cells by characterization of the three-dimensional structures obtained. A total of 52 ears in 33 normal subjects (18 males and 15 females; mean age 51 years) was examined. The volume of pneumatization in the temporal bone, as measured by CT, ranged from 2.08 to 20.05 ml (mean 6.40 +/- 4.09). The morphological characteristics of air cells in the three-dimensional images were examined with reference to the volume of air cells and the direct on of their growth. The three-dimensional structures were observed from four directions (lateral, supralateral, anterolateral and supramedial). Large air cells existed plentifully in all directions. Anteriorly, air cells were growing in two directions; laterally and toward the petrous apex. The growth in the latter direction was especially marked, and this contributed to the growth in the medial direction. Air cells that grew anteriorly had two directions of growth (lateral and toward the petrous apex). The directional difference in growth varied with the ear. On examining the suprainferior growth, air cells that grew large in the anterior direction were found to grow large in the suprainferior direction and those that did not grow large in the anterior direction were found contrarily to grow poorly in the suprainferior direction. With the above morphological characteristics taken into consideration, morphological classification of air cells into five types was attempted by the volume of air cells and the direction of their growth.