Introduction: The pneumatization of the mastoid part of the temporal bone is assigned a major role in the pathogenesis and therapy of middle ear diseases.The trapped air in the mastoid serves as a reservoir, that can alleviate pressure differences in the tympanic cavity. Lack of mastoid pneumatization was emphasized as an unfavorable factor in the development of middle ear diseases. Accordingly, a good pneumatization is considered a favorable factor in middle ear surgery. So far, several pathways of pneumatization of the mastoid process have been discussed: i) genetic predisposition, ii) pneumatization via the activity of the mastoid epithelium and iii) pneumatization via the Eustachian tube, the tympanic cavity and the aditus ad antrum.
Materials and methods: 30 CT scans of patients without known Eustachian tube dysfunction were analyzed. 3D reconstruction and volumetry of the mastoidal trapped air was performed using 3D slicer. Additionally, the cross-sectional area of the aditus ad antrum was assessed. Statistical analysis was performed using SPSS software.
Results: The mean volume of the mastoid air cell system ranged from 329.0mm³ to 14253.2mm³ (mean 5223.65 mm³, SD 3081.7 mm³). The mean cross-sectional area of the aditus ad antrum ranged from 3.1 mm² to 19.5mm² (mean 9.4mm², SD 4.2mm²). We found a good correlation between the mastoid air cell system volume and the cross-sectional area of the aditus ad antrum (r=0.6, p<0.0005).
Discussion: This study showed a good correlation between the opening width of the aditus ad antrum and the pneumatization of the mastoid. Therefore, the cross-sectional area of the aditus ad antrum could be an indicator of a lack of pneumatization of the mastoid and might be a viable surrogate parameter in assessing middle ear disorders.

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