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.

Abstract

<b>BACKGROUND.</b> 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. <b>OBJECTIVE.</b> 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. <b>METHODS.</b> 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 (<i>n</i> = 1535 patients) or the CDCT (median, 7 mSv) group (<i>n</i> = 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 <i>U</i> 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. <b>RESULTS.</b> 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]; <i>p</i> = .93), test-negatives (0.5% [95% CI, -1.5% to 2.5%]; 91.7% [1407/1535] vs 91.2% [1403/1539]; <i>p</i> = .67), sensitivity (0% [95% CI, -6% to 6%]; 95% [110/116] vs 95% [105/111]; <i>p ></i> .99), and specificity (0.3% [95% CI, -0.5% to 0.9%]; 99.4% [1401/1410] vs 99.1% [1397/1409]; <i>p</i> = .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; <i>p</i> = .20). <b>CONCLUSION.</b> Two-millisievert CT is comparable to conventional-dose CT for the diagnosis of right colonic diverticulitis. <b>CLINICAL IMPACT.</b> 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. <b>TRIAL REGISTRATION.</b> ClinicalTrials.gov NCT01925014.