Using a sum of the cross diameters of the appendix measured on ultrasonography as a criterion can more effectively predict acute appendicitis.

Objective: To investigate whether using a sum of the cross diameters on the transverse section of the appendix as a criterion can improve the diagnosis of acute appendicitis (AA).

Methods: In this retrospective study, 433 patients with AA and 207 patients with a normal appendix were assigned to the training and validation groups in a proportion of 7:3. Each group was divided into subgroups consisting of patients with AA and a normal appendix. The training group included 144 patients with a normal appendix and 302 patients with AA, while the validation group comprised 63 patients with a normal appendix and 131 patients with AA. Graded compression ultrasound was performed to evaluate the appendix, and the cross diameters on the transverse section were measured, with one of them used as the maximum outer diameter (MOD).

Results: The cut-off value of the sum of cross diameters for predicting AA was 13.5 mm or more. When it was applied to evaluate the appendix in the training group, a sensitivity of 98.7%, specificity of 99.3%, positive predictive value of 99.7%, negative predictive value of 97.3%, and an area under the receiver operating characteristic curve of 0.990 were achieved. Which were significantly higher than those (except for a sensitivity of 99.3%) obtained using the criteria of MOD ≥ 6 mm. Similar results were obtained in the validation group.

Conclusion: Using a sum of cross diameters of the appendix of 13.5 mm or more as a criterion to diagnose AA can yield excellent diagnostic performance, and can replace the current criteria of MOD of 6 mm or more.

Key Points: Question A MOD of the appendix ≥ 6 mm is a recommended criterion for diagnosing AA, but often results in a false-positive diagnosis. Findings Using the sum of the cross diameters of the appendix ≥ 13.5 mm as a criterion yielded significantly higher diagnostic performance than the recommended criteria. Clinical relevance The sum of the cross diameters of the appendix is a better criterion for the evaluation of patients with suspected AA, exhibiting significantly higher diagnostic performance than the MOD of the appendix.