The potential imaging modalities for diagnosis of acute appendicitis include plain radiographs, ultrasound, and computed tomography. Prior to the widespread use of modern imaging techniques, plain abdominal films were often obtained in patients with abdominal pain, and a right lower quadrant fecalith (or appendicolith) was considered pathognomonic for acute appendicitis. A number of studies question this teaching, however. Teicher and colleagues reviewed the abdominal radiographs of 200 appendectomy patients, 100 with pathologically proven appendicitis and 100 with a normal appendix. Of those with appendicitis, 10.5% had an appendicolith on x-ray, compared to 3.3% of those without appendicitis. An extensive review of appendectomy specimens at the Mayo Clinic showed that fecaliths or appendiceal calculi were present in 9% of patients with nonperforated appendicitis and 21% of those with perforated appendicitis. Interestingly, fecaliths were also present in 7% of patients with suspected appendicitis who had a pathologically normal appendix, and 2% of patients who had an appendectomy for other reasons.
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.