Overtubes: a bridge to successful colonoscopic resection?

Endoscopic resection of colorectal polyps is the established method for the removal of most benign early colorectal neoplasia and even some early superficially invasive cancers. Despite the significant advances in new techniques to facilitate endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD), access to the lesion, particularly in the proximal colon, is sometimes difficult, often resulting in an unstable scope position with poor distal tip control.

The SMSA (Size, Morphology, Site, Access) assessment tool was developed to grade the difficulty of colorectal polyp resection; it can predict the complexity and critical outcomes of EMR [1]. Of the four factors assessed in this tool, only access is potentially modifiable. We can try to improve access and scope stability by using different types of colonoscopes and patient position changes, but when this is unsuccessful, the use of overtubes can potentially improve the “A” component of the SMSA. It could be argued that the use of 1:10 000 adrenaline injected into the polyp head and stalk will reduce the size (S component) of pedunculated polyps, facilitating resection, but experience of this is limited, and this method has not been recommended in guidelines [2].

“In this study, 36% of the patients had diverticulosis, and 25% had previous abdominal surgery, but this did not interfere with technical or clinical success.”

In this issue of Endoscopy, Jawaid et al. prospectively evaluated the efficacy and safety of a rigidizing overtube (ROT) for the resection of colonic and duodenal polyps [3]. The design of this device is significantly different from other overtubes reported previously in that it has two configurations: a flexible position to facilitate insertion and a fixed (rigid) one to provide stability. It is also available in two lengths. In this prospective descriptive registry study, the authors showed that endoscopic resection of complex (>25 mm) colonic polyps using ROT was successful in the majority of cases without needing to resort to alternative resection techniques. The technical success rate of ROT deployment, defined as the ROT being successfully advanced over the endoscope to reach the polyp site, allowing safe manipulation of the lesion, was 100%. The mean time taken to deploy the ROT and reach the polyp site was 7.2 minutes. This was achieved with no complications attributable to the use of the overtube. The results are reassuring and suggest that the insertion and manipulation of this ROT is straightforward. No information is provided in the manuscript about the learning curve, but all three endoscopists participating had previous experience of the ROT in at least 10 cases.

Wei et al. reported for the first time the use of the ROT for difficult and or incomplete colonoscopies and described six cases in which EMR or ESD of large polyps were made possible by using the device [4].

Several comments can be made regarding the insertion of overtubes during colonoscopy. Ideally, they should be advanced over a shortened and straight colonoscope, particularly for rigid overtubes, otherwise insertion can be painful for the patient, and there is a risk of perforation. This was the recommended insertion method with the short overtube developed by Okamoto, which has been widely used in Japan [5]. However, the ROT is extremely flexible in its native state, and both overtube and colonoscope can be advanced easily together even if loops are formed. In this situation, the colonoscope and loop will be reduced by shortening, and then the ROT rigidized before advancing the colonoscope alone again. The variable flexibility of the ROT may have implications on the insertion technique compared with other overtubes, but that will need to be explored in future studies. One of the limitations in the use of overtubes may be the presence of a fixed colonic segment because of adhesions or diverticular disease. In this study, 36% of the patients had diverticulosis, and 25% had previous abdominal surgery, but this did not interfere with technical or clinical success. Nevertheless, it should be noted that all procedures were performed with general anesthesia or modified anesthesia care. Therefore, tolerance to the ROT with no or mild sedation is unknown and this could potentially be a limitation in the use of this device in patients without deep sedation. Finally, electromagnetic scope navigation systems to guide the insertion were not employed in this study and their usefulness in facilitating the adequate insertion of overtubes has surprisingly only been described very briefly in previous studies [6].

Overtubes are expected to be helpful, particularly for the resection of polyps in the proximal colon, and 96% of the polyps treated in this study were proximal to the splenic flexure. Compared with the rectum, where there is always one-to-one transmission of the forward pressure to the tip of the colonoscope, in proximal lesions, the presence of folds, acute angulations, or loops can impair the advancement of the colonoscope and transmission of the movements to the tip of the scope. Considering that >75% of the lesions were in a difficult location and with moderate to severe looping in 45% of cases, the fact that ESD could be completed in most of the lesions with a satisfactory dissection time and speed, en bloc resection rate, and good safety outcomes suggests that the participating endoscopists were highly skilled in ESD and that the ROT facilitated the resections. In fact, the endoscopists felt that the overture helped with stabilization in 98% of cases and noted that it only fell out of position more than three times in only 5% of cases.

Some of the authors in this study also participated in a prospective evaluation of another overtube, which does not have the rigidizing system but is fitted with two balloons allowing for dynamic traction during ESD with the distal balloon [7]. A direct comparison of both systems cannot be made from the results of these studies, but insertion time to the target polyp was similar, and also there were no device-related complications. However, in 8% of the cases, the procedure could not be completed successfully, possibly because of challenges deploying the device. This double-balloon system seems to be more complex than the ROT, but because of its design, it probably offers more possibilities for advanced resection, such as for the application of traction in ESD.

The conduit function of overtubes and ability to retrieve specimens is potentially another significant advantage of these devices. In this study, 22 polyps were resected in a piecemeal fashion; in 10 of them the primary purpose was EMR, and in 12 it was ESD or hybrid ESD. The use of an overtube should facilitate the retrieval of the polyp fragments and this could have obvious and important implications. This information was not provided in the present study but would deserve attention in the future.

The sample size for duodenal polyps was very small in this study, but the overall technical and clinical success rates were modest, and the authors felt that the use of the overtube sometimes hindered the resection.

In the past, endoscopists used ancillary techniques, mainly position changes and external abdominal pressure, to facilitate insertion and obtain a more stable position of the colonoscope [8]. More recently, variable stiffness colonoscopes have facilitated colonoscopy insertion. Moving toward the second quarter of the 21st century with the increased complexity of colonic polyp resections, which even includes bringing robotic instruments to the endoscopy suite, more work needs to be done to enable smooth and stable access to proximal colonic lesions. The ROT presented by Jawaid et al. sounds promising, considering the performance data and safety profile. Well-designed comparative studies with standard practice and other available overtube systems are awaited in order to understand how and when these devices are best incorporated into resection practice and what the implications are on cost-effectiveness.

Publication History

Article published online:
03 September 2024

• References

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