[The volume ratio between squamosal and petrosal air cells divided by Körner's septum]

Pneumatized air cells of the temporal bone are embryologically divided into two portions; the squamosal portion and the petrosal portion. These two portions are anatomically separated by the petrosquamous fissure and petrosquamous lamina, the so-called Körner's septum. In this study, the volumes of the two portions were measured with Target Imaging CT in 5 normal ears (3 subjects) with a clearly recognizable Körner's septum. The combined volume of the two portions, in all CT slices, was also measured. The squamosal portion occupied 32.7% of the total air cell volume, on average, and the petrosal portion was 67.3%. A positive correlation was observed between the total air cell volume of the temporal bone and the volume ratio of the petrosal portion. When the volume of each part was examined according to the CT slice level, from high to low, the maximum volume of the squamosal portion was at the slice level of the epitympanic cavity. The volume of the petrosal portion was prominent at the slice level of the epitympanic cavity and the upper antrum. These results that the petrosal portion plays a more important role than the squamosal portion in pneumatization of the temporal bone. This analysis with Target Imaging CT provides useful information for understanding the middle ear pathology resulting from poor pneumatization of the temporal bone.