Classification of Temporal Bone Pneumatization on Computed Tomography

The pneumatized temporal bone functions as an air reservoir during eustachian tube dysfunction to prevent the middle ear from developing severe negative pressure. Therefore, the degree of pneumatization is an important prognostic factor in planning middle ear surgery. In this study, we looked for useful criteria to evaluate the whole pneumatization of temporal bone on CT scan.

Method: The volume of temporal bone air cells was measured in a three-dimensional reconstruction model using the GE AW 4.0 program (GE Co.) by applying the multiplanar volume rendering technique. In the second aspect of the study, the extension of air cells was classified into four groups according to the lines drawn from the anterior border and middle most-protruded portion and posterior border of the sigmoid sinus. The line was at an angle of 45 degrees toward the anterolateral direction. (1) Hypopneumatization is the pneumatization progressed ahead of the drawing line from the anterior border of the sigmoid sinus. (2) Moderate pneumatization is the pneumatization progressed between the lines drawn from the anterior border and the most-protruded portion of the sigmoid sinus. (3) Well pneumatization is the pneumatization progressed between the lines drawn from the most protruded portion and the posterior border of the sigmoid sinus. (4) Hyperpneumatization is the pneumatization progressed over the posterior boundary of sigmoid sinus.

Next, we examined the difference of the entire volume among the groups at the level of the dome of the superior semicircular canal, MI complex, and IAC, EAC, and the descending carotid artery. There was significant difference in the whole volume among the groups. Further, there was no significant correlation between the cross-sectional area of the antrum and the entire volume of the temporal bone.

Conclusion: We can estimate the degree of the pneumatization of temporal bone easily by evaluating of the air cells around the sigmoid sinus at axial CT image. The result of this study can be helpful in planning tympanomastoidectomy.