The direct signs of acute appendicitis on CT scan with high sensitivity were enlarged appendix with over 6 mm in diameter (93.8%), appendiceal wall thickening (87.5%), appendiceal wall enhancement (90.6%); the signs with high specificity were maximum depth of intraluminal appendiceal fluid greater than 2, 6 mm (100%), appendiceal wall enhancement (87.5%) and appendicolith (87.5%).