Effect of mastoid bone pneumatization on the conformation and depth of the sinus tympani, a high-resolution computed tomography study.

Purpose: To investigate the relationship between mastoid pneumatization and the conformation and depth of the sinus tympani (ST) in patients with chronic otitis media (COM), based on the high-resolution computed tomography (HRCT) scans.

Methods: Two hundred and two patients affected by COM were included in the study. The patients were divided into three groups according to the extent of mastoid pneumatization on HRCT scans; pneumatized (group 1), diploic (group 2) or sclerotic (group 3). The variation in the ST area (types A, B, C) was assessed using a radiomorphological classification based on the relationship between the medial boundary of the ST and the third portion of the facial nerve. Depth of the ST was calculated by measuring the distance between the medial boundary of the ST and medial boundary of the third portion of the facial nerve RESULTS: There was a statistically significant difference between the groups in terms of the type of ST (p < 0.001). The mean depths of the ST were 1.59 ± 0.82 mm (0.00-2.80 mm) in group 1, 1.10 ± 0.79 mm (0.00-3.00 mm) in group 2 and 0.53 ± 0.63 mm (0.00-2.60 mm) in group 3. The groups were significantly different in terms of the depth of the ST (p < 0.001).

Conclusion: A well-pneumatized mastoid is highly associated with a deep and posteriorly positioned ST with respect to the facial nerve. The preoperative HRCT scans of patients with cholesteatoma should be carefully evaluated to determine the conformation and depth of the ST.