Computed tomography and ultrasonography in the diagnosis of appendicitis: When are they indicated?

Hypothesis: Relative merits and indications exist for ultrasonography (US) and computed tomography (CT) in the diagnosis of appendicitis. Design: Prospective study. Setting: General community and tertiary care hospital. Methods: Ninety-nine patients (50 males and 49 females) were studied. Following consent, the initial disposition was recorded, designating the patient for operation, observation, or discharge from the hospital. Each patient was studied by CT and US. Studies were independently evaluated by 2 radiologists, and the results were designated as positive, negative, or equivocal. The surgeon reevaluated patients before and after learning the results of US and CT, recording whether the CT scan, US, or reexamination influenced the final disposition. Results: Fifty patients had appendicitis; 6 appendixes were perforated. The initial clinical impression called for 44 operations, 49 observations, and 6 discharges. Thirty-four patients had their treatment plan changed from the initial disposition. Utrasonography did not affect the initial impression. In contrast, 18 patients were rediagnosed solely on CT scan findings. Seven patients were rediagnosed by reexamination. Of 44 patients initially designated for operation, the CT scan and reexamination spared 6 females from surgery; the negative appendectomy rate potentially decreased from 50% to 17% (P=.03). The CT scan, US, or reexamination failed to spare 2 males from exploration with negative results. Of the 49 patients initially designated for observation, 23 were rediagnosed after reevaluation, 13 were discharged from the hospital, and 10 underwent expedient operation. One patient was spared from inappropriate discharge from the hospital. The reliability of the CT scan was good, with high sensitivities and specificities. Equivocal scan results lowered the diagnostic value. Conclusions: Selective use of a CT scan with a second examination can improve the diagnostic accuracy and management of suspected cases of appendicitis by (a) reducing the negative appendectomy rate in females, (b) moving patients from observation to earlier operation or discharge from the hospital, and (c) preventing inappropriate discharge of patients with appendicitis.