Volume of mastoid pneumatization: Three-dimensional reconstruction with ultrahigh-resolution computed tomography

The volume of the mastoid air cell system was measured in 69 patients with normal middle ears. All patients underwent axial ultrahigh-resolution compu ted tomography. Mastoid pneumatization was marked on each axial slice, and 3-dimensional reconstruction was performed. The volumes were measured with a volumetric algorithm. A polyethylene tubing phantom with a density simila r to that of bone on computed tomography was devised. The polyethylene tubi ng was tied in a particular fashion so as to create interconnecting air spa ces with a known volume. The phantom was scanned with the imaging parameter s used for scanning the temporal bone. The air in the tubing was marked, an d 3-dimensional reconstruction for the marked phantom air was performed. Th e volume of the interconnecting air spaces was measured and found to be ide ntical to its known volume, thereby verifying the accuracy of the method us ed. The mean mastoid volume was 6.61 cm(3). The smallest volume measured wa s 1.3 cm(3). and the largest was 12.7 cm(3). The importance of this techniq ue lies in its high accuracy, ease of use, and ability to directly correlat e mastoid size and clinical findings.