Reduction of perception error by double reporting of minimal preparation CT colon

Minimal preparation CT colon (MPCTC) is a useful test for frail elderly patients, who tolerate full bowel preparation poorly, and has the potential advantage of identifying extra-colonic pathology. Double reporting has been shown to reduce perception errors in a variety of radiological investigations, and we sought to determine its usefulness for MPCTC. A prospective consecutive cohort of 186 patients undergoing MPCTC for lower gastrointestinal symptoms was double reported. Radiologists were blinded to each report. Data for each report were divided into colonic and extra-colonic findings, with the latter being graded as clinically relevant or irrelevant. Discrepancies between the two reports were identified. A positive colonic lesion was defined as one where direct endoscopic visualisation was recommended. A clinically relevant extra-colonic lesion was defined as one that could impact on future patient management. 13% (24/186) of patients had a significant colonic lesion; 7 of these were identified only by 1 observer, although only 1 was confirmed endoscopically to be cancer. The positive predictive value for colon cancer was 69% for single reporting and 54.5% for double reporting. There were 67 clinically relevant extra-colonic lesions, and 25 of these were reported only by only 1 observer. In conclusion, double reporting found one extra-colonic cancer, but at the expense of five unnecessary endoscopic procedures. This seems a reasonable trade-off and we would therefore recommend double reporting. However, implementation would have a significant impact on manpower and service delivery.