Farewell to the cap or is there still an indication?

 

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Colonoscopy continues to be the preferred method of screening for colorectal cancer (CRC) in the United States. It has been shown to be effective in not only preventing CRC but also in decreasing mortality from this disease [1] [2] [3]. This protection rests on the premise that adenomas are premalignant lesions, and that their detection and removal during colonoscopy prevents the development of cancer. The adenoma detection rate (ADR) is therefore considered to be an important quality indicator of colonoscopy and has been shown to be an independent predictor for the risk of developing interval colon cancer after screening colonoscopy [4] [5].

Colonoscopy is not perfect in the detection of adenomas as it is highly operator dependent. Tandem colonoscopy studies have shown that the adenoma/polyp miss rate can be substantial [6]. One of the major reasons for missing adenomas is their location on the proximal aspects of colonic folds. These areas are often difficult to visualize even with a meticulous withdrawal technique. This is due to the limitations of the angle of view of the colonoscope lens, the extent of tip deflection, and the rotational torque that can be applied to the colonoscope shaft. In a computed tomography colonography study, three out of four adenomas missed during colonoscopy were shown to be located on the proximal aspect of a fold [7].

Cap-assisted colonoscopy (CAC) is a simple technique that can assist the endoscopist in examining the otherwise blind mucosal areas on the proximal aspects of folds. The cap is a plastic, hollow, cylindrical, distal attachment that is fitted to the tip of the colonoscope and protrudes 4 mm beyond the tip. The portion of the cap that extends beyond the tip of the colonoscope helps to depress and flatten the folds, thereby bringing the mucosa on their proximal aspects within view of the endoscopist. The cap also helps to keep the colonic mucosa at a distance from the lens and thus prevents a “red out” (loss of visualization due to close approximation of the mucosa to the colonoscope lens), which can obscure visualization. Finally, the cap can also help to stretch and splay the colonic mucosa that might have folded over and obscured small lesions from endoscopic view [8].

In this issue of Endoscopy, Pohl et al. describe a randomized controlled trial (RCT) that evaluated whether CAC improves the ADR [9]. A total of 1113 patients were randomized to undergo either CAC or standard colonoscopy. Of the 10 endoscopists who performed the colonoscopies, 9 had no previous experience of using the cap attachment. Prior to enrolling patients in the study, the endoscopists watched a video demonstrating the use of the cap and were then required to perform at least three cap-assisted colonoscopies. The study showed no difference between the standard and cap-assisted techniques in terms of ADR (42 % vs. 40 %; P = 0.45), number of adenomas per patient (0.89 vs. 0.82; P = 0.43), advanced adenoma detection rate (10 % vs. 9 %; P = 0.59), or number of advanced adenomas per patient (0.12 vs. 0.11; P = 0.54). No significant learning curve was detected when the ADR was evaluated for every 20 colonoscopies performed. Cecal intubation was achieved more rapidly (by 1 minute) with the cap compared with the standard technique (P < 0.001). A higher success rate of terminal ileum intubation was seen with CAC (93 % vs. 89 %; P = 0.028), and the intubation was judged to be “easy” more frequently with the cap (84 vs. 79 %; P = 0.033). Interestingly, the cap had a variable effect on ADR among individual endoscopists; 7 out of the 10 endoscopists showed a numerically higher ADR with the cap, ranging from 1 % to 20 %, but this difference was not statistically significant, and the other 3 endoscopists actually had a lower ADR when using the cap – ranging from 6 % to 15 %. The two endoscopists who preferred the cap over the standard technique had a higher ADR compared with those who did not prefer the cap (51 % vs. 36 %; P = 0.003). There was also a significant trend for increased ADR with longer withdrawal times with the cap, but this trend was not observed with the standard technique. The authors concluded that although the cap cannot be recommended for routine use, it may be suitable for some endoscopists, especially those who prefer it over the standard technique.

Overall, this is a well-conducted RCT and is certainly the largest US study to evaluate CAC. The strengths of the study include appropriate patient selection, relevant study end points, sound methodology, a large sample size, the involvement of multiple endoscopists at two academic centers, and an exhaustive statistical analysis of the results.

However, there are also some limitations that merit discussion. In our opinion, the lack of experience in using the cap among 9 out of 10 endoscopists was a major drawback. Although CAC is a simple technique, it nevertheless requires some learning, practice, and experience. As the cap protrudes 4 mm beyond the tip of the colonoscope, and is not entirely transparent, it may appear to restrict the angle of view to the novice or inexperienced user. The key to CAC is to use the edges of the cap to press down upon and depress the colonic folds. This is achieved by turning the flexible tip of the colonoscope with the dials and by applying rotational torque to the shaft. By this maneuver, the mucosa on the proximal aspect of the folds is exposed. If this is not performed appropriately and effectively during withdrawal, then the presence of the cap can tend to be counterproductive, as it does decrease the angle of view.

The authors mention that all endoscopists who had no previous experience of the cap viewed a video demonstrating the technique and then performed at least three CAC procedures. Although there are no data to suggest how many procedures are required to gain competence with the device, performing only three procedures does not appear to be sufficient to gain proficiency. Moreover, it might have been worthwhile if these procedures by the inexperienced endoscopists were viewed and evaluated by an expert, with feedback provided in situations where the correct technique was not being employed. It is quite possible that, in the absence of feedback to rectify or improve their technique, these endoscopists did not show improvement in their ADR with increasing number of cap procedures. However, one of the strengths of the study is that 10 endoscopists participated, thereby making the results potentially more generalizable to clinical practice. Although the authors did analyze the learning curve by comparing the ADR for every 20 colonoscopies performed, the study may not have been adequately powered for this, as 6 out of 10 endoscopists performed fewer than 100 colonoscopies. In two previous studies that showed improvement with the use of the cap [10] [12], the procedures were performed by endoscopists trained in the use of the cap. Another limitation of the Pohl et al. study was that the number of procedures performed was not equitable between the different endoscopists, with one of them performing more than 20 % of the procedures. In addition, fewer procedures were deemed to have “excellent” or “good” bowel preparation in the cap arm, which could have negatively affected the ADR in this group. However, the results of this well-conducted trial do dampen our enthusiasm regarding the use of cap to improve ADR.

The effect of the cap attachment on ADR has been evaluated in several studies, the majority of which were conducted in Asia ([Table 1]) [9] [10] [11] [12] [13]. At least three RCTs have been performed in Western countries. In the first study – a randomized, tandem study from the United States – Hewett and Rex demonstrated that CAC was associated with a lower adenoma miss rate than standard colonoscopy [12]. This was followed by another study by Rastogi et al., in which 420 patients were enrolled and randomized to CAC or standard colonoscopy [10]. The authors demonstrated an improved ADR (69 % vs. 56 %; P = 0.009) as well as an increase in the number of adenomas detected per patient (2.3 vs. 1.4; P < 0.001) when using the cap. de Wijkerslooth conducted an RCT that included 1380 patients and compared CAC with standard colonoscopy. The cap-assisted technique failed to significantly improve the ADR (29 % vs. 29 %) or the number of adenomas detected per person (0.49 vs. 0.5) [11]. Only one study, to our knowledge, has shown a lower ADR with the cap compared with the standard technique [12]. The major limitations of this particular study were that the bowel preparation was less satisfactory and the withdrawal time was shorter in the CAC arm, both of which could have negatively impacted on the ADR. A comparison of the major studies shows no significant difference in the cap characteristics, withdrawal time, or bowel preparation ([Table 1]) [9] [10] [11] [12] [13]. A large meta-analysis by Ng et al. showed that CAC detected a significantly higher proportion of patients with polyps compared with the standard technique (52.5 % vs. 47.5 %; relative risk [RR] 1.08) [14], although no significant difference was seen for ADR (46.8 % vs. 45.3 %; RR 1.04).

Although the focus of the majority of the studies evaluating CAC has been ADR, the cap attachment can confer some ancillary advantages related to cecal intubation times, cecal intubation rates, and patient discomfort. A meta-analysis of 10 studies showed that the cecal intubation time was significantly shorter (mean difference – 0.64 minutes) when using the cap compared with the standard technique [14]. The current study by Pohl et al. also showed a shorter cecal intubation time in the CAC group. The cap helps to negotiate sharp turns and bends in the colon by keeping the mucosa away from the lens, thereby preventing a “red out” or loss of visualization, which can often occur in these areas. The cap can also help with luminal orientation and better anticipation of the luminal direction. Moreover, the cap serves as a mechanical anchor, hooking the folds and thereby helping to reduce loops in the colonoscope. This can make the insertion easier and more efficient. Studies have also objectively evaluated patient discomfort during colonoscopy with and without the cap. Some have shown a lower level of patient discomfort with the cap while others have shown no difference [11] [15]. CAC can also be used as a salvage procedure in cases where the cecum could not be reached using the standard technique. Lee at al. performed a study where patients in whom the cecum could not be reached during the initial procedure (CAC or standard) underwent a second colonoscopy by the alternative method [13]. CAC achieved a higher rescue rate of cecal intubation compared with the standard technique (67 % vs. 21 %).

Another advantage of the cap is apparent during endoscopic mucosal resection (EMR) of polyps. In an RCT of patients undergoing EMR of adenomas, the mean time required for resection of one polyp was significantly shorter in the cap group (3.5 vs. 4.2 minutes; P = 0.01), with subgroup analysis showing a significant difference particularly in nonpedunculated polyps [16]. In our experience, the cap can be valuable during EMR by helping to stabilize the colonoscope and by keeping the polyp at a constant distance from the lens, as well as assisting in submucosal injection by exposing the edges of flat lesions.

In conclusion, although this well-conducted study by Pohl et al. did not show any overall improvement in ADR when using the cap, we are far from bidding farewell to this simple accessory. In our opinion, CAC can still be a useful technique for some endoscopists by helping to improve their ADR. This is especially the case for those who can master the technique and make use of the mechanical advantage afforded by the cap to flatten the folds, and for those who prefer using it during colonoscopy, as was shown in the Pohl study. Furthermore, it can be useful when negotiating a difficult colon, assist in faster intubation of the cecum, and be used as a rescue method in cases of failed cecal intubation with the standard technique. In addition, it can also assist the endoscopist during EMR. Further studies are necessary to evaluate in greater detail the reasons for the wide variability in ADR when using the cap and to investigate ways to improve the detection rates of endoscopists with low ADRs when using the device. Further assessments are also required to determine whether there are certain subgroups of patients undergoing colonoscopy who might benefit more from the use of the cap.

• References

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