Introducing the ratio of cross diameters of the appendix for ultrasound diagnosis of acute appendicitis can significantly increase specificity.

Abstract

To validate whether the introduction of the ratio of the cross diameters on the transverse section of the appendix (RATIO) ≤ 1.18 is useful for improving the ultrasound diagnosis of acute appendicitis (AA). Data from 220 patients with AA and 110 patients with a normal appendix were retrospectively studied. The RATIO ≤ 1.18, maximal outer diameter (MOD) > 6mm, and a combination of RATIO ≤ 1.18 and MOD > 6mm were used for predicting AA. The area under the receiver operating characteristic curve (AUC), sensitivity, specificity, positive and negative predictive values (PPV and NPV) were calculated. The RATIO ≤ 1.18, MOD > 6mm, and a combination of RATIO ≤ 1.18 and MOD > 6mm for predicting AA showed a sensitivity of 90, 100, and 90%; specificity of 79.1, 27.3, and 88.2%; and AUC of 0.845, 0.636, and 0.891, respectively. When comparing the outcomes between MOD > 6mm and a combination of MOD > 6mm and RATIO ≤ 1.18, the specificity and PPV increased from 27.3 to 88.2% and 73.3 to 93.8%, respectively (all P < 0.0001). The sensitivity and NPV decreased from 100 to 90% and 100 to 81.5%, respectively (all P < 0.0001). The AUC increased from 0.636 to 0.891 (P < 0.0001). When comparing the AUC of MOD > 6mm, and a combination of RATIO ≤ 1.18 and MOD > 6mm for predicting AA with the AUC in a previous study, there were no significant differences between each other (all P > 0.05). Introducing the RATIO ≤ 1.18 for the evaluation of AA can improve the diagnostic performance and significantly increase specificity.