CT's impact in diagnosing appendicitis depends on clinical likelihood

Clinical experience shows that diagnostic CT reduces the incidence of negative appendectomies. Those skeptical about the application's safety, however, may find ammunition in a recent prospective study that suggests CT may be unnecessary when appendicitis is unlikely.

Dr. Robert O. Nathan, an acting assistant professor of radiology at the University of Washington in Seattle, and colleagues assessed the impact of CT of the appendix on 100 consecutive adult patients who presented with symptoms suggesting appendicitis in the emergency room of a 300-bed community hospital.

Patients under age 18, pregnant women, and patients at risk for a reaction to intravenous contrast media were excluded. All subjects experienced right lower quadrant pain for less than five days and had white cell counts greater than 10,000/mm³.

Appendicitis was confirmed by surgical pathology results in 17 of 19 patients who underwent appendectomy. One surgical patient with a normal appendix had equivocal findings on CT, and the other underwent appendectomy despite normal CT results.

The results indicated to Nathan and colleagues that CT of the appendix had an important therapeutic impact. The initial ER treatment assessment was altered for 29% of the cases, including 29 patients who were discharged because of CT findings. None returned later for surgery.

CT did not have a big impact, however, on the 57 patients who were initially designated for discharge. The disposition of only two of these patients changed after the CT results were known.

CT ruled out appendicitis in 12 of 23 (52%) patients when appendicitis was considered probable and in 60% of patients when appendicitis was considered very likely. When appendicitis was considered unlikely, CT ruled it out in 100% of patients (20 of 20). The study appeared in the October issue of the American Journal of Roentgenology (2008;191:1102-1106).

Nathan and colleagues determined that CT may not be appropriate when some clinical indications of appendicitis are absent.

"The data suggest that CT should be performed in patients in whom emergency clinicians consider appendicitis to be probable or very likely. It could be withheld in patients in whom emergency clinicians rate appendicitis as unlikely," Nathan said.

If physicians used that strategy, 20% of the CT examinations would have been eliminated with no false negatives. Overall sensitivity and specificity of CT were 94% and 100%, respectively.

Dr. Robert Novelline, director of emergency radiology at Massachusetts General Hospital, points out that CT can still be useful in many cases.

"The CT scan will show the alternative diagnosis, which could be a renal stone, which could be diverticulitis, which could be epiploic appendagitis," he said.

But Nathan and colleagues wonder in their report if CT's benefits are always worth its risks.

"CT entails cost, radiation exposure to the patient, and, if IV contrast material is used, risk of contrast reaction or contrast-induced nephropathy," they said.

For more information from the Diagnostic Imaging archives:

Ultrasound could precede CT in acute appendicitis triage

Report from ARRS: Benefits of abdominal CT in the emergency room outweigh radiation risks

MSCT helps find perforated appendicitis

— by Rebekah Moan