• Acute Appendicitis: Meta Analysis of Diagnostic Performance of CT and Graded Compression US Related to Prevalence of Disease

    Radiology: Volume 249: Number 1—October 2008

    Adrienne van Randen, MD Shandra Bipat. MSc, PhD Aeilko H. Zwinderman, PhD DirkT. Ubbink, MD, PhD
    Jaap Stoker, MD, PhD Marja A. Boermeester, MD, PhD

    Purpose: This study was a head-to-head comparison of graded com­pression ultrasonography (US) and computed tomography (CT) in helping diagnose acute appendicitis with an em­phasis on diagnostic value at different disease prevalences, commonly occurring in various hospital settings.

    Materials and Methods:MEDLINE, EMBASE, CINAHL, and Cochrane databases were searched from January 1966 to February 2006. Pro­spective trials were selected if they (a) compared graded compression US and CT in the same patient population; (b) included more than 10 patients, otherwise, the study was considered a case report; (c) evaluated mainly adults or adolescents; (d) used surgery and/or clinical follow-up as reference standard; and (e) reported data to calculate 2 X 2 contingency tables for graded compression US and CT. Estimates of sensitivity, specificity, and positive and negative likelihood ratios (LRs) for US and CT were calcu­lated. Posttest probabilities after CT and US were calcu­lated for various clinically relevant prevalences.

    Results: Six studies were included, evaluating 671 patients (mean age range, 26-38 years); prevalence of acute appendicitis was 50% (range, 13%-77%). Positive LR was 9.29 (95% confidence interval [CI]: 6.9, 12.6) for CT and 4.50 (95% CI: 3.0, 6.7; P = .011) for US, yielding posttest probabili­ties for positive tests of 90% and 82%, respectively. Nega­tive LR was 0.10 (95% CI: 0.06, 0.17) for CT and 0.27 (95% CI: 0.17, 0.43) for US (P = .013), resulting in post-test probabilities of 9% and 21%, respectively. Posttest probabilities for positive tests were markedly decreased at lower prevalences.

    Conclusion: In bead-to-head comparison studies of diagnostic imaging, CT had a better test performance than did graded com­pression US in diagnosing appendicitis. Ignoring the rela­tionship between prevalence (pretest probability) and di­agnostic value may lead to an inaccurate estimation of diagnostic performance.