The diagnosis of acute appendicitis is a clinical one, and given a typical presentation, imaging is not necessary. Often, however, the clinical picture is less than classic, and then imaging can be extremely helpful. An exception to this is the detection of an appendicolith by plain film in the setting of acute RLQ pain. Other imaging such as barium enema and abdominal CT are sometimes used, but have limitations. CT is good for the detection of perforation and abscess formation, it is relatively poor for acute uncomplicated appendicitis.
Barium enema has a significant high false positive and negative rate.
Tc99m -wbc scan has limited use. Scanning is begun over the point of maximal tenderness, gradually increasing pressure to scan deep structures in both longitudinal and axial slices. The presence of a fecolith is also taken as a positive sign. The absence of mucosal folds or peristalsis is important in order to differentiate from cecum or ileum. It is less sensitive in cases of perforated appendix, however.