Conventional-Dose CT Versus 2-mSv CT for Right Colonic Diverticulitis as an Alternate Diagnosis of Appendicitis: Secondary Analysis of Large Pragmatic Randomized Trial Data

BACKGROUND. Adoption of low-dose CT for the diagnosis of appendicitis has been slow in children and in adults, partly because of concern about missing alternative diagnoses including right colonic diverticulitis. OBJECTIVE. The purpose of our study was to retrospectively compare the diagnostic performance of IV contrast-enhanced 2-mSv and conventional-dose CT (CDCT) for the diagnosis of right colonic diverticulitis in adolescents and young adults with suspected appendicitis. METHODS. This post hoc analysis of a prospective randomized controlled trial included 3074 patients (1672 female patients and 1402 male patients) ranging in age from 15 to 44 years old (mean ± SD, 28 ± 9 years) from 20 hospitals. From December 2013 to August 2016, patients were randomized to either the 2-mSv CT group (n = 1535 patients) or the CDCT (median, 7 mSv) group (n = 1539 patients). A total of 161 radiologists prospectively issued CT reports in which they suggested alternative diagnoses for 976 (2-mSv CT) and 924 (CDCT) patients. Seven independent assessors adjudicated final diagnoses on the basis of clinical and CT findings. Endpoints of test-positives, test-negatives, sensitivity, and specificity for right colonic diverticulitis were compared using chi-square and Mann-Whitney U tests. Characteristics and disposition of patients with test-positive results were assessed. Four readers retrospectively reviewed CT images of 400 patients selected from the trial (113 and 108 patients with diverticulitis from 2-mSv CT and CDCT groups, respectively) to evaluate interobserver agreement for right colonic diverticulitis in terms of Gwet coefficients. RESULTS. Between-group differences were minute for most endpoints related to right colonic diverticulitis: test-positives (difference, 0.2% [95% CI, -1.8% to 2.1%]; 7.8% [119/1535 patients] vs 7.6% [117/1539 patients]; p = .93), test-negatives (0.5% [95% CI, -1.5% to 2.5%]; 91.7% [1407/1535] vs 91.2% [1403/1539]; p = .67), sensitivity (0% [95% CI, -6% to 6%]; 95% [110/116] vs 95% [105/111]; p > .99), and specificity (0.3% [95% CI, -0.5% to 0.9%]; 99.4% [1401/1410] vs 99.1% [1397/1409]; p = .66). The characteristics and disposition of test-positive patients were similar between the two groups. Gwet coefficients were high and comparable between the two groups (2-mSv CT vs CDCT, 0.849 vs 0.889; p = .20). CONCLUSION. Two-millisievert CT is comparable to conventional-dose CT for the diagnosis of right colonic diverticulitis. CLINICAL IMPACT. By mitigating concern about a missed diagnosis of right colonic diverticulitis, the results further support the use of low-dose CT in patients with suspected appendicitis. TRIAL REGISTRATION. ClinicalTrials.gov NCT01925014.