Wide View and Retroview During Colonoscopy

Colonoscopy is the best imaging device currently available for the detection of lesions in the large bowel, but may be an imperfect tool against colon cancer. Because recent guidelines for colorectal cancer screening and surveillance depend on whether polyps are found on colonoscopy and on their size, the need to identify all the neoplasia in the colon has assumed greater importance. This article reviews and assesses the latest developments in colonoscopy including wide-angle optics, endoscope caps and hoods, retroflexion and the use of the third eye retroscope.

Colonoscopy has long been considered the gold standard for evaluation of the colon, as not only can it locate and find lesions throughout the large intestine, but therapy is also possible during the procedure. Unfortunately, time has shown that colonoscopy may be a flawed gold standard, as lesions may be missed and carcinomas may not be prevented. In an editorial, Dr David Lieberman stated that “the data on colonoscopy accuracy is a humble reminder of the limitations of colonoscopy.” Despite the known diagnostic accuracy of colonoscopy, this examination may miss some colonic lesions.

Colonoscopy became popular soon after it was introduced because it was a considerably better tool than barium for colonic evaluation. However, early in the infancy of this combined diagnostic and therapeutic procedure, investigators questioned the accuracy of this gold standard. It was decided that the best way to test the accuracy of colonoscopy was to have a procedure performed and immediately afterward have a repeat examination by the same or a different endoscopist. Thus the patient would serve as his or her own control and permit the discovery of any lesions missed by the first examiner.

The concept of “tandem colonoscopy” is best suited for evaluation of a discrete lesion such as a polyp because this is a quantifiable object with a defined size, shape, and location in the colon. If seen and removed, biopsied, or photographed, there is no mistake that it is present. During these investigations, the first examiner removes all polyps that are encountered so that all polyps seen by the second endoscopist will represent overlooked lesions. One drawback to tandem colonoscopy is that the interventionists are totally aware that this study is under way and will pay special attention to the intraluminal pathology so as not to miss lesions. Despite the heightened awareness by virtue of participating in a tandem colonoscopy experiment, the 3 trials that specifically evaluated the possible “miss” rate of polyps in the large bowel revealed strikingly large numbers of polyps overlooked by the first examiner using standard colonoscopic equipment.

The first report of back-to-back colonoscopies on the same day and immediately following each other was in 1991. The next report of tandem colonoscopy appeared 6 years later, and the most recent was in 2008. The overall miss rates for adenomas in the earlier studies were 15% to 24%. The large multicenter European study found that the miss rate for all polyps was 28%, for hyperplastic polyps 31%, and for adenomas 21%. However, the miss rate for all polyps equal to or larger than 5 mm was 12% and for adenomas 9%. Among the 14 polyps and 6 adenomas larger than 5 mm missed during the first examination, 5 polyps and 1 adenoma were sessile, and 9 polyps and 5 adenomas were flat. In all, 37 adenomas were overlooked in 286 patients with the median size being 3 mm; however, the range of missed lesions was from 1 to 18 mm. In this European study, 3 advanced adenomas were missed with a size from 15 to 18 mm. The investigators reported that there was a 27% rate of missed adenomas for lesions smaller than 5 mm in diameter, and the miss rate for lesions greater than 5 mm in diameter was 9%. In a previous study of 183 patients having tandem colonoscopy, Rex and colleagues reported a 27% miss rate for polyps smaller than 6 mm in diameter and only 6% for polyps larger than 9 mm. There was no significant difference between in the miss rate of polyps in the right colon (27%) and the left colon (21%). Although a substantial percentage (24%) of adenomas was missed, there was an inverse ratio between the miss rate and the size of the adenoma. In the summary of the report, Rex and colleagues recommended that technology be developed that may overcome the technical limitations of colonoscopy.

Another way of evaluating whether polyps were missed on an initial colonoscopic examination is to repeat the colonoscopy at an interval time, not on the same day as the original procedure. In a retrospective analysis of more than 15,000 colonoscopies, the polyp miss rate was evaluated by comparing findings on repeat colonoscopic examinations at 4 and 12 months after the initial colonoscopic examination. The calculated miss rate for all polyps was 17% and for neoplastic polyps 12%. Retrospective studies such as this are not as elegant as tandem examinations, but the findings are similar: polyps are missed during the initial colonoscopy.

The problem with missed colonoscopic neoplasms is primarily due to their location, being on the proximal aspect of folds; this means that the technique of the examination is critically important in the discovery of colon polyps. It has been shown that not all missed lesions are “hidden” because flat neoplasms can elude detection by the casual or untrained observer, even when they are in the field of view of the straightforward viewing standard colonoscope. Pickhardt and colleagues did a computed tomographic colonography (CTC) evaluation of more than 1200 persons who had same-day CTC and colonoscopy. With segmental unblinding during a colonoscopic examination that followed the CTC, 10% of polyps were found only after they were originally missed by colonoscopy but detected on the original CTC. Of the missed neoplasms found on the second-look colonoscopy after segmental unblinding, 17 were tubular adenomas, 3 were tubulovillous adenomas, and 1 was a small adenocarcinoma (size range 6–17 mm). The majority of these neoplasms were located on the edge or on the proximal aspect of a fold. A more recent article from London on CTC simulation reconstructions using a 90° imaging field of view corroborated a previous report which showed that 23.4% of the colonic surface is not visualized by direct straight end-on examinations. The report by East and colleagues repeated the type of scan by Pickhardt and colleagues but with simulated varying fields of view of 90°, 120°, 140°, and 170° to match the angle of view of some colonoscopes. In addition, a simulated retrograde view was obtained with a 135° field of view, equivalent to retrograde viewing by the third-eye retroscope (TER). In this study, the percentage of visualized colonic surface increased with each increasing angle of view increment. The total number of missed areas was approximately the same for fields of view of 90° to 140°, but decreased when the field of view was 170°. Approximately only 85% of the colonic surface would be visualized using a 140° angle of view, and this increased so that more of the surface would be seen when the examination was repeated using a 170° angle of view comparable to the Olympus 180 series colonoscopes (Olympus Medical Instruments, Tokyo, Japan). The simulated addition of a retrograde viewing auxiliary imaging device led to an almost complete surface visualization, with a tenfold decrease in the area that was missed compared with that obtained using a wide-angle colonoscope with a 170° angle of view. With the simulation of optical colonoscopy by CTC software, using the commonly available 140° angle of view of most colonoscopes, approximately 13% of the colonic surface is unseen. Simulation of a colonoscope with a 170° field of view resulted in an almost 6% reduction in percentage of surface missed. The marked additional mucosal visualization seen in the simulation models with a combination of 140° forward and a 135° reverse view (such as that provided by the TER) may actually be preferred to recently developed optics providing a 360° view (Aer-O-Scope), which has a substantial “fish eye effect.” In this simulation model, there does not seem to be any additional benefit to using a colonoscope with 170° angle of view instead of a 140° instrument when associated with the additional advantage of the TER.

Barthel, in an editorial in Gastrointestinal Endoscopy , mentions that to attempt an increase in the finding of adenomas, there have been several articles written on the use of a wide-angle lens on a colonoscope. At present, most colonoscopes have a 140° angle of view, but only one manufacturer has a standard production model colonoscope with a 170° angle of view (Olympus Medical Endoscope, Tokyo, Japan) ( Figs. 1 and 2 ). An evaluation of a 15-mm diameter colonoscope with a 210° angle of view, in which the lens projects from the endoscope tip permitting an ultrawide angle of view, has been performed. With this instrument, the viewing angle could be converted to 160° for close inspection of the mucosal surface. This study included 50 patients randomized to the ultrawide-angle colonoscope compared with a standard colonoscope with a 140° angle of view. There was no difference between the 2 types of colonoscopes in the detection of adenomas, but the miss rate for polyps was somewhat lower with the ultrawide-angle colonoscope. It is interesting that of two examiners, one found no difference in adenoma detection between the 2 types of colonoscopes, but the second examiner missed more polyps with the ultrawide-angle colonoscope than when using a colonoscope with a 140° angle of view. The investigators concluded that the principal deficit of the extremely wide-angle colonoscope was that the resolution was significantly reduced when compared with standard colonoscopes.

A randomized tandem colonoscopy study in 50 patients comparing a colonoscope with a 170° angle of view with a 140° instrument demonstrated that the miss rate for all polyps with the wide-angle colonoscope was similar to the miss rate with the standard colonoscope. In this study, 50 patients were randomized to have colonoscopy with the standard instrument first (140° angle of view) or to have colonoscopy with the wide-angle instrument as the first examination. The miss rate for all polyps with the wide-angle colonoscope was not statistically different from the miss rate for all polyps with the standard colonoscope. It should be noted that neither of the tested instruments were high-definition instruments, and the only parameter that was different between the 2 endoscopes was the angle of view of the lens. The conclusion of the investigators was that “in comparison with other innovations for reducing polyp miss rates during colonoscopy … wide angle colonoscopy may be the least effective strategy.” A similar conclusion was reached by a group from Spain who randomized, in a one-to-one ratio, 620 patients into those having colonoscopy with a wide-angle high-definition instrument versus procedures using a standard colonoscope. This study showed no significant difference in the number of adenomas detected by either instrument. A study with 8 colonoscopists at 2 institutions randomized 710 patients using a standard (140° angle of view) colonoscope and a 170° wide-angle instrument. Neither instrument had a high-definition component. The primary end point of this study was to see if there was a reduction in withdrawal time using the wide-angle instrument as compared with the standard colonoscope. The mean insertion time for the 2 instruments was similar, at approximately 5 minutes, but overall the mean withdrawal time was shorter with the wide-angle colonoscope than with the standard colonoscope (4.9 vs 5.4 minutes); however, the shorter withdrawal time was only statistically significant for 3 of the 8 endoscopists. In this study, the proportion of patients with at least one adenoma was significantly higher for the standard instrument than for the wide-angle colonoscope. However, there was no difference in the mean number of adenomas detected with either instrument. The conclusion was that although there was a 30-second reduction in mean withdrawal time using wide-angle instruments, the benefits of the wide-angle colonoscope “appeared minimal on close inspection.”

In contrast to the majority of reports, a nonrandomized study from Prague compared wide-angle high-definition colonoscopy with standard-angle (140°) instruments with and without high definition. A total of 507 patients were involved in the study, which showed that the wide-angle high-definition instrument detected more adenomas, flat adenomas, and adenomas with advanced histology as compared with both instruments with a 140° angle of view. The instruments were not randomly assigned in this study, but the mean rate of adenomas and flat adenomas found per patient was significantly higher in the wide-angle high-definition colonoscopic group compared with the other groups, and in the right colon was almost double that found with the standard-angle colonoscopes. The currently available 170° wide-angle instrument also has a high-definition component. The question arises as to whether the high-definition component increases the ability of the examiner to find more polyps and adenomas than can be found with the wide-angle component alone.

A retrospective report from the Cleveland Clinic compared endoscopic findings in more than 400 individuals who underwent examination with a wide-angle high-definition colonoscope and compared them with a group who had conventional colonoscopy (non–high definition) with a 140° angle of view that were matched for gender, age, and indication for colonoscopy. This study was not randomized, and polyps were detected in 39.9% of the subjects in the high-definition/wide-angle group and in 36.9% of those in the conventional colonoscopy group. The investigators concluded that wide-angle high-definition colonoscopy afforded no increase in the detection of polyps or adenomas over conventional colonoscopy with 140° angle of view, and that the improved resolution and wider angle of view does not increase the ability to see polyps and adenomas.

Another study reported a large randomized trial but did not show any objective advantage of the high-definition instrument using narrow-band imaging over the same wide-angle high-definition scope using white light imaging. Only hyperplastic polyps were found to be more frequent in the group for whom narrow band imaging was used. Other investigators using tandem colonoscopy and either narrow band imaging or white light (both with wide-angle high-definition instruments) found that the neoplasm detection rates were similar when the mucosa was viewed with narrow-band imaging or white light. The conclusion was that they did not find narrow-band imaging to significantly influence the likelihood of missing or detecting a colorectal neoplasm as compared with white light.

During evaluation of the wide-angle instruments, multiple comparisons have been made to study whether there is any significant difference in cecal intubation with the 170° colonoscope as compared with one with a 140° angle of view. The 2 instruments being compared in several reports were identical in every aspect except for the angle of view. In one study, the mean insertion time to the cecum was shorter with the wide-angle colonoscope than with the standard colonoscope (2.09 vs 2.53 minutes). Similarly, the mean withdrawal time was shorter with the wide-angle instrument (4.98 vs 5.74 minutes) than with the standard colonoscope. Colonoscopists in a dual-center study also looked at the insertion time of a standard colonoscope versus a wide-angle colonoscope. The mean insertion time was similar, and the mean withdrawal time of the wide-angle instrument was somewhat shorter than for the standard colonoscope, 4.9 minutes versus 5.4 minutes, respectively. Another study with the wide-angle instrument determined that its use resulted in a more rapid examination, with the mean time for examination with the wide-angle colonoscope being 6.75 minutes versus 7.64 minutes with the standard colonoscope. During this evaluation the aim was to withdraw the standard or the wide-angle colonoscope as rapidly as possible while yet being able to examine the entire lumen and the proximal side of any fold or structure. The mean extubation time with the wide-angle colonoscope was reduced by 25% to 30% as compared with the 140° instrument. Another report compared the standard colonoscope with the wide-angle colonoscope, and found no statistical difference in either intubation or withdrawal time between the 2 instruments when a minimal 6-minute extubation time was mandated. The reports in the medical literature confirm that the extubation time may be up to 1 minute shorter with a wide-angle colonoscope because of the ability to expose a greater surface area than can be visualized with an instrument having a 140° angle of view. However, this does not translate into a clinically meaningful advantage unless it results in a greater polyp-finding capability. The polyp miss rate has been investigated (vide supra) and there has been no significant difference shown in the probability of missing polyps as adenomas, whether the instrument used had a wide-angle as opposed to a narrower angle of view.

In the continuing quest to find changes in design, techniques, or accessories to make the colonoscopic examination more efficient, a cap or hood in the instrument has been investigated. The use of this device keeps the tip of the scope from contacting the mucosal surface to prevent obstruction of vision when the scope tip is deflected around a fold or a bend in the colon. The cap could be of use to flatten folds and thus see lesions that grow behind folds unseen by standard straightforward colonoscopy. It was the consideration that a clear plastic cap could be used as an extension of the colonoscope’s tip while permitting the portion of mucosa that is deflected to be seen through the transparent hood ( Fig. 3 ).