Assessment of the volume of the mastoid air cell system using digital image processing.

Abstract

There has been a great deal of controversy concerning the development of pneumatization in the temporal bone. Many reports on the size of the mastoid air cell system have been discussed a planimetric X-ray method, however , there have been no techniques for direct volume measurement based on high-resolution computed tomography (CT) . Discussion of the relationship between ear disease and pneumatization of the temporal bone requires three-dimensional measurement of the temporal bone in vivo. Recently, we developed such a technique by using digital image processing to measure the volume of the mastoid air cell system. With this technique , only the air cells and tympanic cavity, with a gray scale level similar to air outside the skull were easily selected on the CT films. Then, after image processing called "thresholding" , only the areas and volumes of these extracted pneumatized parts were calculated . The volumes of the pneumatized parts of the temporal bone were calculated separately as partial volumes divided by several CT planes .The sum of the partial volumes was calculated as the total volume of the aerated cavity . This technique also made it possible to reconstruct a three-dimensional (3D) model of the air cell system for visual presentation.CT images of 43 normal temporal bones were analyzed. The average volume temporal bone pneumatization (including air cells and tympanic cavity) was about 6ml. There were no differences between pneumatization on the two sides in either sex.Comparisons of partial volumes of pneumatization in the temporal bone revealed that the volumes of portions including the tympanic cavity and its surrounding air cells and those of the antrum and its surrounding air cells were larger than those of other portions. 3D models of the air cell system revealed a variety of shapes. These findings indicated that this technique is not only useful for quantitative analyses but for easy subjective morphological analyses.

The Relationship between Traumatic Tympanic Membrane Perforations and Pneumatization of the Mastoid

“…Thus, people who have a wide mastoid system and an open eustachian tube have a greater risk of perforation of the tympanic membrane, due to the decreased protective role of air as a cushion [10]. While Ito et al [20] in their series of 25 cases found the mean total volume of 41 temporal bone air cells to be 4.05 B 1.59 ml, Isono et al [21] reported that it was 6 ml in 43 normal temporal bones. They did not observe any difference between the volumes of the right and left sides and between the two sexes.…”

Positional relationship between the facial nerve and other structures of the temporal bone

“…The method of evaluating pneumatization in this study was precise and convenient, and differed from the previous studies. [11][12][13][14][15][16][17][18] The volume of pneumatization including air cells and tympanic cavity was calculated and found to be similar to other studies. [13][14][15][16][17][18] It was found x The authors speculate that this information may be of help to surgeons that there were correlations between the pneumatization and all the measured parameters of the facial nerve.…”