More adenomas – less cancer? Advanced imaging in colonoscopy

High quality colonoscopy is a prerequisite for effective colorectal cancer (CRC) screening programs. During recent years, a lot of emphasis has been put on improvement of colonoscopy quality to increase the quality of screening programs. A number of key quality indicators have been proposed for colonoscopy. These include the quality of bowel preparation, cecum intubation rate, withdrawal time, completeness of polyp removal, patient safety and satisfaction, and adenoma detection rate (ADR).

The ultimate goal of CRC screening is to prevent cancer incidence and death. A proxy for this is the risk of interval cancer (CRC occurring after a screening colonoscopy). Interval cancers after colonoscopy are often due to missed adenomas at screening [1]. Therefore, the detection of adenomas has been a primary target for colonoscopy quality improvement during recent years [2]. The ADR is the only quality indicator from the above list that has an established association with interval cancer. Two large-scale studies have shown that high ADRs are associated with low risk of interval cancer [3] [4]. Therefore, a major interest in the field of colonoscopy has been to improve ADRs.

ADRs can be improved by a number of measures, including new technical tools, which aim to improve the image quality of colonoscopes and thereby improve detection rates. A lot of research in recent years has focused on improving endoscopes to enhance image quality by the addition of advanced technical features such as electronic altering of endoscope light emission (narrow-band imaging, full-spectrum endoscopy [FUSE; EndoChoice Inc., Alpharetta, Georgia, USA], and i-Scan [Pentax, Tokyo, Japan]), high definition resolution, or magnification (such as in confocal laser endomicroscopy) [2] [5]. These techniques aim to improve the image quality during colonoscopy and thus enable the endoscopist to see small, subtle, or flat adenomas in areas that are visualized with traditional standard white light endoscopy.

Another approach to increase the detection of adenomas and thereby decrease the risk of interval cancer is to address the fact that a significant percentage of the colonic mucosa is not visualized during standard colonoscopy. These blind spots obviously decrease the sensitivity of colonoscopy to detect adenomas, serrated polyps, and even cancer. Studies that have used computed tomography colonography to simulate the standard colonoscopy 140° – 170° angle view have shown that standard colonoscopes fail to visualize 10 % or more of the colonic mucosal surface [6]. The rate of adenomas missed because of limited visualization has been shown to be highest for adenomas that are located on the proximal side of folds, the proximal colon and the rectum, or near colonic flexures [7].

This issue of Endoscopy features a first clinical feasibility study of a novel colonoscope with extra-wide angle of view [8]. The novel colonoscope has a lateral-backward viewing lens (144° – 232°) in addition to the standard 140° forward-viewing lens of standard colonoscopes. The views from both lenses are displayed on a single monitor, as a single image. In 47 patients, 28 adenomas were found (most of them small – mean diameter 3.3 mm). The lateral-backward lens detected 16 out of the 28 adenomas before they were visualized using the standard forward-viewing lens. The lateral-backward lens was most effective in the ascending and the sigmoid colon [8].

The study was a single-arm feasibility study and did not apply the gold standard design for this type of diagnostic sensitivity study, which is the back-to-back tandem design. Therefore, to understand the clinical value of this new tool, it now needs to be subjected to back-to-back tandem studies comparing it with other technologies recently developed to decrease blind spots during colonoscopy. A main competitor is the FUSE system, which has recently been shown in a large, randomized, multicenter tandem trial to increase adenoma detection [9]. Other devices that should undergo head-to-head comparison trials are the Endocuff (Arc Medical Design Ltd, Leeds, UK), cap-assisted colonoscopy, and the Third-Eye probe (Avantis Medical Systems Inc., Sunnyvale, California, USA) [9] [10] [11]. These devices are not integrated into the colonoscope, which is a major drawback. Other drawbacks include impaired suction and biopsy ability for the probe-base tools, and increased tip diameter for the devices attached to the endoscope tip. 

The advantage of the novel technique described in this issue of Endoscopy compared with the FUSE technology is the view from both lenses displayed in a single image. This may improve user friendliness and thereby acceptance by the endoscopy community. A drawback may be that the new instrument has a large tip diameter and may therefore be associated with more patient discomfort compared with standard colonoscopes. In addition, as the results of the present study show, the thicker endoscope tip may cause problems with retroflexion in the rectum.

Special consideration should be paid to the double-edged sword of more sensitive technology leading to increased adenoma detection. Although a higher ADR is desirable in reaching our goal of reducing CRC incidence and death, it is not a free lunch. More sensitive colonoscopes will increase the number of individuals who are diagnosed with adenomas. Most of these additional adenomas will be small and will not harbor a large risk of malignant transformation. Increased adenoma detection will lead to a larger number of individuals referred for surveillance colonoscopy, which in turn will increase the demand for resources and the risk for complications and side-effects associated with colonoscopy and polypectomy.

Presumably, the additional individuals diagnosed with adenomas by using wide-angle technology will be at low risk of developing CRC. Applying current surveillance guidelines to these new patients may be too much, too often [12]. The reclassification of individuals from adenoma free to adenoma bearer by more sensitive endoscopes may induce what is known as the Will Rogers phenomenon – an upstaging of patients by applying more sensitive technology, without clinical gain [13] [14]. The endoscopy community needs to be aware of these mechanisms to avoid increasing costs and exposure of patients to unnecessary colonoscopy.

• References

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