Antibiotics for computed tomography (CT)-confirmed uncomplicated acute appendicitis is a safe and feasible treatment alternative highlighting the importance of accurate pre-interventional differentiation between uncomplicated and complicated appendicitis. CT is the gold standard in assessing appendicitis severity. The aim of this study was to assess potential prognostic CT factors for complicated acute appendicitis.

A large prospective patient cohort was collected in concurrence with enrollment in two randomized clinical trials between April 2017 and November 2018 with CT-diagnosed acute appendicitis with both available histopathology and surgical diagnosis. The main aim was to evaluate the effect of appendiceal diameter on appendicitis severity. Other assessed CT variables included appendiceal wall enhancement defect and fluid and edema around the appendix. A subgroup analysis on patients without an appendicolith was performed.

The main analysis included 3085 patients with CT-diagnosed appendicitis, and there were 1965 patients without an appendicolith in the subgroup analysis. In both analyses, wider appendiceal diameter (p < 0.001) and appendiceal wall enhancement defect (p < 0.001) were associated with increased risk of complicated acute appendicitis. No clear cut-off point for appendiceal diameter association with complicated appendicitis could be determined. Among patients without an appendicolith, appendiceal wall enhancement defect had an odds ratio (OR) of 3.39 (95% confidence interval [CI] = 2.10 to 5.50) for complicated appendicitis.

Wider appendiceal diameter and appendiceal wall enhancement defect on CT are objective imaging findings associated with an increased risk of complicated acute appendicitis. These findings and risks should be acknowledged by clinicians when selecting the optimal treatment alternative for each patient and assessing whether a patient is suitable for non-operative treatment.