Mastoid and middle-ear cavity opacification in CT: Proposal of a diagnostic algorithm to predict acute mastoiditis.

Aim Mastoid opacification is a common incidental imaging finding. It may be a sign of acute mastoiditis (AM) requiring prompt treatment up to surgical intervention. We aimed at stratifying visually semantic as well as quantitative imaging features to differentiate unspecific mastoid opacification versus AM and to propose a decision tree for clinical patient management.

Materials and Methods We included 48 patients (male, 28; female, 20; mean age, 59.5 ± 18.1 years) with mastoid opacification (AM, n = 24; control, n = 24) who underwent clinically indicated cerebral CT between 12/2007 and 07/2018 in this retrospective study. Semantic features described the extend and asymmetry of mastoid and middle-ear cavity opacification as well as complications like erosive changes. Minimum, maximum and mean Hounsfield unit (HU) values were obtained as quantitative features. We analyzed the features employing univariate testing. Highest ranked features were applied to build decision trees.

Results Erosive changes were only rarely seen and did not reach the level of significance (Likelihood Ratio (LR) = 0.015). Highest significance was found for asymmetric mastoid or middle-ear cavity opacification (LR < 0.001). Applying a specific threshold of the extent of opacification, we reached significance levels of LR = 0.042 and 0.002 for mastoid and middle-ear cavity opacification. AM cases had higher maximum and mean HU values (p = 0.009, p = 0.024). We built two decision trees to include either visually semantic features or visually semantic features and the quantitative feature maximum. The performance was comparable and promising with levels of accuracy and sensitivity of 0.867, 0.9 or 0.833, 1.0, respectively.

Conclusions We propose two simple to follow and clinically applicable three step decision trees to raise suspicion of AM if mastoid opacification is seen in clinical routine. We could demonstrate inferiority of classical descriptors like erosive changes.

Publication History

Article published online:
11 May 2021