New CT criterion for acute appendicitis: maximum depth of intraluminal appendiceal fluid

The purpose of this study was to evaluate whether a new criterion-maximum depth of the intraluminal appendiceal fluid-is useful to differentiate between a normal appendix with diameter greater than 6 mm and appendicitis without periappendiceal inflammation.

The study included 59 patients showing a normal appendix with diameter greater than 6 mm and having no adjacent lesions (noncomplicated-normal-appendix group), 30 patients showing a normal appendix with diameter greater than 6 mm and having adjacent lesions (complicated-normal-appendix group), and 38 patients showing appendicitis without periappendiceal inflammation (appendicitis group). The following specific CT findings were retrospectively evaluated: maximum appendiceal diameter greater than 6 mm, maximum appendiceal wall thickness greater than 3 mm, appendiceal wall enhancement, focal cecal wall thickening, adjacent adenopathy, appendicolith, and maximum depth of the intraluminal appendiceal fluid.

The mean maximum depth of the intraluminal appendiceal fluid in the appendicitis group was significantly higher than in the two groups with a normal appendix (Mann-Whitney U test: p < 0.001). When using maximum depth of the intraluminal appendiceal fluid greater than 2.6 mm for a criterion of appendicitis, sensitivity and specificity for differentiation between the appendicitis group and the other two groups with a normal appendix were both greater than 80%. In contrast, when using another CT a criterion, either sensitivity or specificity was 50% or less.

The new CT criterion based on the maximum depth of the intraluminal appendiceal fluid greater than 2.6 mm is particularly useful for differentiating appendicitis without periappendiceal inflammation from a normal appendix with a diameter greater than 6 mm.