Assessment of Mastoid Air Cell Size Versus Sigmoid Sinus Variables with a Tomography-assisted Digital Image Processing Program and Morphometry

We assessed the mastoid air cell size and variables of the sigmoid sinus in healthy ears and ears with chronic otitis media (COM). Thirty-eight patients with unilateral COM [15 with cholesteatoma (COM/+) and 23 without cholesteatoma (COM/-)], and 20 subjects with healthy ears, were included in the study. Assessment was performed using a quantitative digital image processing computed tomography (CT) program, and the volume of the mastoid bone was measured using the morphometric method of Cavalieri. In both COM/+ and COM/- patients the sigmoid to suprameatal spine distance and mastoid size were greater on the healthy side than on the diseased side ( p<0.05). The distance and area were significantly greater in the healthy control subjects than in either the healthy or the diseased ears of the patients with COM ( p<0.05). In the healthy ears of COM patients, there was significant correlation between the sigmoid to suprameatal spine distance and air cell size and mastoid volume ( p<0.05). In the diseased ears of COM patients, this correlation was absent ( p>0.05). The sigmoid sinus shape was of the half-moon type (62%), protrusive type (22%) and saucer type (16%). The digital image processing CT program allowed us to estimate the individual area of the air and soft tissue filled mastoid air cells. The mastoid size in both intact and disease ears of COM patients was smaller than in the healthy controls. The mastoid size may be determined genetically. However, environmental factors such as infection may also affect the mastoid size. Therefore, both genetic and environmental factors may be related to COM as far as the size of the mastoid air cells is concerned.