Acute appendicitis is one of the commonest causes of an ‘‘acute abdomen’’ and appendectomy is the commonest emergency surgical operation performed worldwide. The two diagnostic CT signs of acute appendicitis are:

1. unequivocal identification of an abnormal appendix: usually fluid-filled with a slightly thickened and circumferentially enhancing wall and dilated more than 6 mm in transverse diameter
2. an appendicolith associated with pericaecal inflammatory stranding