Appendicitis Imaging Studies

Localized air-fluid levels, localized ileus, or increased soft tissue density in the right lower quadrant is present in 50% of patients with early acute appendicitis. Less common findings are a calculus, an altered right psoas shadow, or an abnormal right flank stripe. The finding on plain films of a calculus in the right lower quadrant coupled with pain in this area strongly supports a diagnosis of appendicitis. Although perforated peptic ulcer is by far the most common cause of free intraperitoneal air, free air is also a rare manifestation of perforated appendicitis. In general, however, the findings on plain films are nonspecific and rarely of help in diagnosis. A suggestion that barium enema may contribute to the diagnosis has not been supported by experience.

A spiral CT examination of the appendicitis may be of help in diagnosis. An enlarged appendix with wall thickening or enhancement or periappendiceal fat stranding are the most useful CT findings of acute appendicitis. Other findings may be present including focal cecal thickening, appendicoliths, extraluminal air, intramural air, and pericecal phlegmon, but are less reliable. CT scans are of greatest value in patients with less than typical clinical and laboratory findings, where a positive study would be an indication for appendectomy. In the face of typical time course of disease, right lower quadrant pain and tenderness plus signs of inflammation (eg, fever, leukocytosis), a CT scan would be superfluous and, if negative, even misleading. Ultrasound imaging is much less reliable than CT. When appendicitis is accompanied by a right lower quadrant mass, an ultrasound or CT scan should be obtained to differentiate between a periappendiceal phlegmon and an abscess.