The clinical signs and symptoms of appendicitis are usually typical. However, nearly a third of patients have atypical findings on clinical examination, which has led to the use of imaging to assist in diagnosis.
Ultrasound and CT have both been recommended for evaluating patients with possible appendicitis.
Ultrasound has a reported sensitivity of 90%. The abnormal appendix is noncompressible, has an outer diameter of 7mm or more, and may contain an appendicolith. Hypoechoic masses adjacent to the appendix raise the possibility of periappendiceal abscess. Unfortunately, adequate imaging may not always be possible due to severe abdominal pain, muscle guarding, or obesity.
Using thin-section helical CT technique and colonic distention with rectal contrast material, the appendix can be identified in most individuals. In prospective trials for the detection of appendicitis, CT has a sensitivity of 96% to 98% and a specificity of 83% to 89%.
The appendix originates from the medial side of the apex of the cecum. The wall of the appendix is no more than 3mm thick and no more than 6mm in diameter. The normal appendix usually has no luminal contents but may contain a small amount of gas or contrast material administered prior to the CT examination. The periappendiceal fat is of normal density.
In mild appendicitis, the wall is thickened and the surrounding fat shows ill-defined increased density due to edema. As the inflammation becomes more severe, adjacent structures show inflammatory changes. The terminal ileum may become thickened and small bowel obstruction may develop . CT is useful in distinguishing abscess from phlegmon by demonstrating the space-occupying nature and the typical contrast-enhancing wall typical of abscess. Periappendicular air is indicative of an abscess and can be detected either by CT or abdominal radiographs. |
