Acute appendicitis: Clinical outcome in patients with an initial false-positive CT diagnosis

Purpose: To investigate the clinical outcome in patients with a diagnosis of appendicitis at computed tomography (CT) in whom treatment is deemed unnecessary after clinical evaluation. Materials and Methods: After institutional review board approval, 2283 patients (856 men, 1427 women;mean age, 46 years;age range, 18-99 years) who underwent CT because they were suspected of having appendicitis between 2002 and 2007 were retrospectively identified. CT reports were reviewed, and the likelihood of appendicitis was assigned a score on a five-point scale:score 1, definitely absent;score 2, nonvisualized appendix with no secondary signs of inflammation; score 3, equivocal;score 4, probable;and score 5, definitely present. Diagnosis of appendicitis at CT was considered a false-positive result if the CT report was classified as probable or definite appendicitis but the patient was not treated within 4 days. Cases with false-positive results were reviewed by two readers blinded to patient outcome, supporting clinical data, and prospective scan interpretation, and a grade was assigned by using the same scale. Medical records were reviewed to determine outcomes. Descriptional statistics were used. Results: Overall, 516 (23%) of 2283 patients had CT findings of probable or definite appendicitis. Thirteen (3%) of 516 patients did not receive immediate treatment for appendicitis. Of these, five (38%; 95% confidence interval:18%, 65%) underwent later appendectomy with proved appendicitis after a mean interval of 118 days (range, 5-443 days). Seven (54%) of 13 patients never developed appendicitis across a mean follow-up of 583 days (range, 14-1460 days). One (8%) of 13 had a normal appendix at eventual surgery. Conclusion: Five of 13 patients with CT findings of appendicitis and reassuring clinical evaluation results in whom immediate treatment was deferred ultimately returned with appendicitis. In patients with CT results positive for appendicitis and benign or atypical clinical findings, a diagnosis of chronic or recurrent appendicitis may be considered.