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

Objective: 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.

Methods: 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.

Results: 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.

Conclusions: 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.