Realizing the problem of missed lesions, endoscopists have attempted to increase the amount of mucosa directly visualized. This thrust originally started in the rectum, where retroflexion was readily performed, and previously unseen areas were brought into view by purposely making a 180-degree rotation in the rectal ampulla.
There have been few studies on the yield of finding significant pathology during rectal retroversion. A paper from the Indianapolis group examined rectal retroversion in 1,502 consecutive patients enrolled in a study of several aspects concerning rectal retroversion. Retroflexion was successful in approximately 94% of patients, but it was not performed in 6% because the rectum appeared narrow. During this study, 7 polyps were visualized by retroflexion only (following a careful, planned extubation of the colonoscope, with special attention to the rectal mucosa right down to the anal verge). Of these polyps, 6 were hyperplastic sessile polyps and 1 was a 4-mm sessile tubular adenoma. In spite of this finding, most gastroen- terologists are committed to the concept of performing rectal retroversion before or after total colonoscopy in order to visualize the area surrounding the dentate line and the distal rectum. Although there have been reports of perforation related to rectal retroversion and several reports of closing those perforations with clips, I recommend performing rectal retroversion, as it need not be uncomfortable nor place the patient at risk.
Should the patient complain of pain when the instrument is advanced into the rectum, that particular attempt should be abandoned and another direction chosen for retroflexion. Occasionally, the rectal vault may be small, a physical feature more common among patients who undergo radiation therapy to the pelvis, patients with inflammatory bowel disease, or slender women. Rectal retroversion may not be possible in these individuals; if it is attempted and is painful, the attempt should be stopped to avoid perforation.
The main reason that retroflexion is performed by endoscopists is to visualize more of the mucosal surface, particularly those areas that are not well seen by direct, end-on examination with a standard colonoscope.
It is possible to purposefully perform retroflexion of the instrument throughout various parts of the colon in a fashion similar to the one more routinely used in the rectum during colonoscopic examination. A comparison between a colonoscope with a shorter tip (or a more acutely angled bending section) and a pediatric or standard colonoscope showed that the prototype instruments were significantly better at performing retroflexion throughout the colon than a standard pediatric colonoscope. The success rate of performing retroflexion in the cecum was 57% for the standard pediatric colonoscope and 91% and 94% for the prototype instruments. There was a 98% success rate for all instruments in terms of intubation of the terminal ileum. The rationale behind the quest for creating an instrument that can be easily retroflexed and yet is a useable instrument for colonoscopy is to detect polyps and adenomas that may be hidden behind folds. As retroflexion is not readily performed above the rectum, areas in the valleys between folds are often not amenable to inspection during colonoscopy with an obligatory straightforward-viewing angle, whether that angle is 140 degrees or 170 degrees.