Ascending colon rotation following patient positional change during CT colonography: a potential pitfall in interpretation.

OBJECTIVE: To investigate the degree and pattern of ascending colonic rotation as patients moved from supine to prone positions during CTC.
METHODS: A search of our CTC and colonoscopy database found 37 patients (43 eligible lesions) who fulfilled the following criteria: colonoscopy-proven sessile polyps ≥ 6 mm in the straight mid-ascending colon, lesion visualisation in both supine and prone CTC, and optimal colonic distension. A coordinate system was developed to designate the polyp radial location (°) along the luminal circumference, unaffected by rotation of the torso. The degree/direction of polyp radial location change (i.e. ascending colonic rotation) between supine and prone positions correlated with anthropometric measurements.
RESULTS: Movement from supine to prone positions resulted in a change in the radial polyp location of between -23° and 79° (median, 21°), demonstrating external rotation of the ascending colon in almost all cases (2° to 79° in 36/37 patients and 42/43 lesions). The degree/direction of rotation mildly correlated with the degree of abdominal compression in the anterior-posterior direction in prone position (r = 0.427 [P = 0.004] and r = 0.404 [P = 0.007]).
CONCLUSION: The ascending colon was usually found to rotate externally as patients moved from supine to prone positions, partly dependent on the degree of abdominal compression.