Primary 2D Versus Primary 3D Polyp Detection at Screening CT Colonography

Disparate results from the existing large CT colonography (CTC) trials suggest that 2D polyp detection is less sensitive than 3D detection, but no direct evidence exists to support this claim. Our goal was to assess the sensitivity of primary 2D polyp detection with cases from the Department of Defense CTC screening trial and compare results with the primary 3D evaluation and previous 2D CTC trials. Ten radiologists, blinded to polyp findings, retrospectively interpreted 730 consecutive colonoscopy-proven CTC cases in asymptomatic adults using a primary 2D approach, with 3D reserved for problem solving. Primary 2D CTC performance was compared with the primary 3D CTC results from the original trial of 1,233 asymptomatic adults. The 10 2D reviewers were significantly more experienced in CTC interpretation (> 100 cases interpreted) than the six reviewers from the original 3D trial. Primary 2D CTC sensitivity for adenomas > or = 6 mm was 44.1% (56/127), compared with 85.7% (180/210) at 3D (p < 0.001). Sensitivity of 2D CTC for adenomas > or = 10 mm was 75.0% (27/36) compared with 92.2% (47/51) at 3D (p = 0.027). Similar sensitivity trends were seen for the by-patient analysis and for all polyps at the 6-mm and 10-mm thresholds. By-patient specificity for 2D evaluation at the 10-mm threshold was 98.1% (676/689), compared with 97.4% (1,131/1,161) at 3D evaluation (p = 0.336). Primary 2D CTC is less sensitive than primary 3D CTC for polyp detection in low-prevalence screening cohorts. The disappointing 2D sensitivity in this study was very similar to results obtained with primary 2D evaluation in previous CTC trials.