Screening colonoscopy is used widely in the prevention of colorectal cancer. Among the quality indicators governing the efficacy of colonoscopy, the ADR and MAP are important indicators that may lead to a decrease in the rate of interval cancer [9, 11]. Although several methods, such as Endocuff, Endocuff-Vision, or Endorings, have been studied for these two quality indicators [15]; in countries with a National Health Insurance System, there are limitations in adopting these methods for private clinics. Therefore, it is important to determine whether the ADR can be increased using conventional methods.
In this study, the combination colonoscopy, including modified cap-assisted and water-exchange colonoscopy with prone position, was effective in the detection of polyps and adenomas, especially those in the proximal colon. These results may have been associated with the synergistic or complementary effects during the insertion and withdrawal phases.
During the insertion (water exchange) phase, the transparent hood prevents the occlusion of the suction channel by creating a space between the mucosa and the suction port; besides, the continuous water exchange prevents the settlement of debris onto the cap attachment. This interaction enables uninterrupted water exchange and a clear visualization during the insertion phase. Also, combination colonoscopy induces a synergistic effect, resulting in the prevention of loop formation and facilitation of cecal intubation by the following mechanisms: 1) the cap-assisted colonoscopy provides better visualization of the lumen in the colonic flexures and the sigmoid colon, facilitating the advancement of the endoscope without forming excessive loops and inadequate air insufflation [21], 2) the water-exchange colonoscopy minimizes the colonic distension, facilitating the advancement of the endoscope without forming excessive loops, 3) prone positioning, owing to the patient’s body weight, provides generalized abdominal pressure; it may allow the passage of the colonoscope in specific instances, such as when large loops, that are otherwise challenging to resolve, form in the transverse colon [16, 22]. While these effects may not facilitate the effective inspection of the mucosa directly, they enable the effective movement of the colonoscopic tip and allows the endoscopist to concentrate, without exhaustion, particularly while inspecting the mucosa during the withdrawal phase.
On water-exchange colonoscopy, mucosal inspection was effortless during the withdrawal phase because of the improved quality of cleanliness [13], while on cap-assisted colonoscopy, the proximal aspect of the colon, especially the proximal side of mucosal folds on the proximal colon and the inner curvatures of the colonic flexures, could be better visualized because of the flattening of the haustral folds [23–25]. This may explain why the proximal MAP, but not the distal MAP, showed a significant increase in the CWP group. We also used a modified version of the cap-assisted colonoscopy, referred to as the “hooking and dragging maneuver” [20]. The conventional cap-assisted colonoscopy flattened a single mucosal fold [26], while the modified cap-assisted colonoscopy hooked (gentle bending of the tip of the colonoscope towards the wall of the colon) and dragged (gentle retraction of the colonoscope, dragging the multiple folds of the colon) multiple mucosal folds simultaneously [20]. This modified method simultaneously allowed the inspection of the proximal and distal parts of the mucosal folds, minimizing blind spots. Figures 1, 2 and 3 shows the use of the hooking and dragging maneuver in locating hidden polyps in multiple cases, correlated with real-world cases.
The ‘a-1’ and ‘b-1’ shows the view without the ‘hooking and dragging maneuver’. In this view, the polyp, which is at the proximal side of the mucosal fold, is hidden. However, when ① hooking (gentle bending of the tip of the colonoscope towards the wall of the colon) and ② dragging (gentle retraction of the colonoscope dragging the multiple folds of the colon) is performed (a-2), the hidden polyp at the proximal side of the mucosal fold becomes visible (b-2). The arrowhead (b-1) indicates the position where the polyp was hidden.
The ‘a-1’ and ‘b-1’ shows the view without the ‘hooking and dragging maneuver’. In this view, LST, which is between mucosal folds, is hidden. However, when hooking and dragging is performed (a-2), the hidden LST between the mucosal folds becomes visible (b-2). The arrowhead (b-1) indicates the position where LST was hidden. The submucosal injection is being administered (b-3), and the endoscopic mucosal resection (EMR) is being performed (b-4).
The ‘a-1’ and ‘b-1’ shows the view without the ‘hooking and dragging maneuver’. In this view, the LST, overlying multiple mucosal folds, is hidden. However, when hooking (a-2) and dragging (a-3) is performed, the hidden LST overlying the multiple mucosal fold becomes visible (b-2). The arrowhead indicates the position where LST was hidden (b-1).
The submucosal injection is being administered (b-3), and the endoscopic mucosal resection (EMR) is being performed (b-4).
In this study, the ADR in the CWP group (70.1%) as well as in the CC group (49.2%) were higher than that of previous studies with 40.5% in cap-assisted colonoscopies (meta-analysis) [27], 41.7% in water exchange colonoscopies (network meta-analysis) [13], and 44% in cap-assisted water immersions (single-center trial) [28]. The high ADR in both groups could be associated with the high quality colonoscopy with long withdrawal time. The significantly longer withdrawal time in the CWP group compared to the CC group was not only due to the additional time required for subsequent polypectomies that resulted from high detection rates but also because of the “hooking and dragging maneuver” in the modified cap-assisted colonoscopy.
In the MAP, the total and proximal MAP in the CWP group was significantly higher than that in the CC group (1.69 ± 1.93 vs 1.06 ± 1.59, P < 0.001; 1.24 ± 1.63 vs 0.55 ± 1.01, P < 0.001). This effect may be related to the characteristics of the proximal colon—a greater height of the haustral fold and more residual debris than the distal colon. In the proximal colon, the use of cap-assisted colonoscopies and water-exchange colonoscopies can facilitate withdrawal inspection by flattening the semilunar folds and improving the quality of cleanliness, respectively.
According to the study by Yen et al. [10], investigating the combination colonoscopy without the prone position, the ADR for the combination of the water-exchange and cap-assisted colonoscopies was 75% (PDR, 93.0%; proximal colon ADR, 61%; adenoma per colonoscopy, 2.70) and was consistent with the ADR of this study. However, the MAP (1.69 ± 1.93) of this study was lower than the MAP (2.70 ± 3.27) obtained in their study [10]. Considering that most of the participants in the study by Yen et al. were males (male, 95; female, 5), we evaluated PDR, ADR, MAP and proximal MAP according to sex. In this study, the PDR, ADR, and MAP in males were 92.1%, 82.8%, and 2.28 ± 2.24, respectively. The high ADR in both studies demonstrated that the combination of cap-assisted and water-exchange colonoscopies facilitated the detection of adenomas by the aforementioned synergistic or complementary effects. Yen et al. used Olympus PCF-H180AL colonoscope (Olympus Medical Systems Corp. Shinjuku City, Tokyo, Japan), with variable stiffness capability, in patients without changing their posture to the prone position, however, the prone position can be helpful while using a colonoscope without variable stiffness capability.
This study had some limitations. First, this was a retrospective study and was performed in a single center; hence, the potential selection or information bias may have existed. Second, we could not investigate the patients’ family history of colorectal cancer and insertion time, which could have influenced ADR [29, 30], and body mass index, which could have led to an increase in loop formation [31]. Third, the endoscopists were non-blinded to the methods used in this study, which may have been a potential source of investigator bias. Fourth, only two of the endoscopists participated in this study, and they performed only one method according to their skill proficiency.