Two Millisievert Versus Conventional-Dose 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 due to the concern of missed alternative diagnoses including right colonic diverticulitis. Objective: To retrospectively compare the diagnostic performance between 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 ranging 15-44 years old (28 ± 9 years; 1672 women, 1402 men) from 20 hospitals, randomized into 2-mSv (n = 1535) or CDCT (median, 7 mSv; n = 1539) groups from December 2013 to August 2016. A total of 161 radiologists prospectively issued CT reports in which they suggested alternative diagnoses in 976 (2-mSV CT) and 924 (CDCT) patients. Seven independent assessors adjudicated final diagnoses based on 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 test-positive patients were assessed. Four readers retrospectively reviewed CT images of 400 patients selected from the trial (113 and 108 with diverticulitis from 2-mSv CT and CDCT groups, respectively) to evaluate inter-observer agreement for right colonic diverticulitis in terms of Gwet's coefficients. Results: Between-group differences were minute for most endpoints related to right colonic diverticulitis: test-positives (difference [95% CI], 0.2% [-1.8%, 2.1%]; 7.8% [119/1535] vs 7.6% [117/1539]; P = .93), test-negatives (0.5% [-1.5%, 2.5%]; 91.7% [1407/1535] vs 91.2% [1403/1539]; P = .67), sensitivity (0% [-6%, 6%]; 95% [110/116] vs 95% [105/111]; P > .99), and specificity (0.2% [-0.5%, 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's coefficients were high and comparable between the two groups (0.849 vs 0.889; P = .20). Conclusion: 2-mSv CT is comparable to conventional-dose CT for the diagnosis of right colonic diverticulitis. Clinical Impact: By mitigating concern of missed diagnosis of right colonic diverticulitis, the results further support the use of low-dose CT in patients with suspected appendicitis.