Added value of ratio of cross diameters of the appendix in ultrasound diagnosis of acute appendicitis

Abstract

BACKGROUND The maximum outer diameter (MOD) of the appendix is an essential parameter for diagnosing acute appendicitis, but there is space for improvement in ultrasound (US) diagnostic performance. AIM To investigate whether combining the ratio of the cross diameters (RATIO) of the appendix with MOD of the appendix can enhance the diagnostic performance of acute appendicitis. METHODS A retrospective study was conducted, and medical records of 233 patients with acute appendicitis and 112 patients with a normal appendix were reviewed. The MOD and RATIO of the appendix were calculated and tested for their diagnostic performance of acute appendicitis, both individually and in combination. RESULTS The RATIO for a normal appendix was 1.32 ± 0.16, while for acute appendicitis it was 1.09 ± 0.07. The cut-off value for RATIO was determined to be ≤ 1.18. The area under the receiver operating characteristic curve (AUC) for diagnosing acute appendicitis using RATIO ≤ 1.18 and MOD > 6 mm was 0.870 and 0.652, respectively. There was a significant difference in AUC between RATIO ≤ 1.18 and MOD > 6 mm (P < 0.0001). When comparing the combination of RATIO ≤ 1.18 and MOD > 6 mm with MOD > 6 mm alone, the combination showed increased specificity, positive predictive value (PPV), and AUC. However, the sensitivity and negative predictive value decreased. CONCLUSION Combining RATIO of the appendix ≤ 1.18 and MOD > 6 mm can significantly improve the specificity, PPV, and AUC in the US diagnosis of acute appendicitis.