A comparison between area and volume measurements of the mastoid air spaces in normal temporal bones.

In a study of 26 normal cadaveric temporal bones, a significant correlation was found between the area of the mastoid air spaces assessed from a conventional lateral radiograph and the mastoid volume as determined using high resolution computed tomography. The relationship, which was found to be linear, is of the form V = 0.82 A + 0.13. The correlation coefficient is 0.95 with a residual standard deviation about the regression of 1.14 cm3. It is apparent, therefore, that an accurate assessment of the mastoid air space volume can be obtained by means of a simple and routinely requested investigation, i.e. the 35 degree lateral oblique radiograph.