Detailed Description:

Colonoscopy is routinely performed for detection and removal of colorectal adenomas, thereby preventing colorectal cancer(CRC).The adenoma miss rates(AMR) still ranges between 26%-62%,and missed adenomas may contribute to the development of interval CRC.Therefore, there is currently considerable interest in improving AMR during a colonoscopy.The second examination has recently attracted increasing attention.since it only requires a relatively short procedure time and does not require any specialized equipment.Thus, we performed an randomized controlled trial (RCT) in patients undergoing colonoscopy for screening to determine the impact of second examination of the proximal colon on AMR compared to conventional examination. This study aimed to determine the impact of second examination of the proximal colon on AMR compared to conventional examination.Consecutive patients aged 40-75years undergoing colonoscopy for screening.Patients were excluded if they failed cecal intubation, prior colorectal resection, inadequate bowel preparation quality (Boston Bowel Preparation Scale (BBPS)scores < 2 in any segment of the colon), inflammatory bowel disease or intestinal tuberculosis, familial polyposis syndrome, coagulation dysfunction, or polyp retrieval failure. Consecutive patients aged 40-75years undergoing colonoscopy for screening.Tandem withdrawal was used in the proximal colon.The colonoscope was inserted in a standard manner. After successful insertion in the cecum, the colonoscope was slowly withdrawn to the splenic flexure and the mucosa was carefully observed, the polyps that were found were removed for histopathologic examination(first pass).Once the splenic flexure was reached, the position of splenic flexure was marked by creating a suction mark or taking a small biopsy. Subsequently, the colonoscope was advanced to the cecum again, additional polyps were removed from the proximal colon during the second withdrawal(second pass). When the colonoscope completed the two forward view examination of the proximal colon (defined as proximal to the splenic flexure), patients were randomly assigned to either the second examination(SE) or the conventional examination(CE) group. The randomization sequence was computer-generated and concealed in sequentially numbered sealed opaque envelopes, at this moment, the envelope was opened. For patients in the SE group, the colonoscope was reinserted into the cecum, additional polyps were removed from the proximal colon during the third withdrawall(third pass), and the remainder of the colon from splenic flexure to rectum was examined in a standard manner. For patients in the CE group, the colonoscope was withdrawn directly from the splenic flexure to the rectum, and polyps that were found were removed. Multiple diminutive hyperplastic polyps (≤ 5 mm) in the sigmoid colon and rectum were not subjected to removal, and only one representative polyp biopsy was analyzed. We recorded all adverse events at the time of the colonoscopy and for one week there after The cecal intubation time and withdrawal time were recorded by an assistant with a stopwatch. The time for polypectomy and biopsy were excluded from the withdrawal time. The primary outcome measure was proximal AMR,defined as the number of proximal adenomas detected in the second pass（CE group）or the third pass（SE group）divided by the total number of proximal adenomas detected during the tandem colonoscopy.}}