Introduction

Underwater endoscopic mucosal resection (UEMR) has been increasingly utilized due to its clinical benefits. However, in patients with poor bowel preparation, UEMR is limited by impaired endoscopic visualization due to luminal turbidity. Viscoclear®, a gel designed to secure endoscopic fields, has been available in Japan since 2020 and has demonstrated a 92.2% effectiveness rate in improving visibility during bleeding or inadequate bowel prep. While its usefulness during UEMR has been anticipated, clinical evidence remains limited. We conducted an image analysis study to evaluate the visibility enhancement effect of gel immersion compared to underwater.

Aims & Methods

This study was a prospective randomized crossover trial to compare the endoscopic visibility of colorectal adenomatous lesions (6-20 mm) between under-water and under-gel observation. Each lesion was observed alternately in both settings using white light imaging (WLI), blue laser imaging (BLI), and linked color imaging (LCI). Color difference (ΔE) between tumor and adjacent non-tumor areas was calculated using the Lab color space in Photoshop (Adobe Systems Inc.) to evaluate lesion margins. Based on preliminary retrospective data from our institution, a sample size of 72 was calculated (power: 0.8, one-sided α: 0.05). (jRCTs062220033)

Results

Between July 2022 and May 2024, 72 lesions were enrolled. Median tumor size was 8 mm (range: 6–18 mm). Histopathology revealed 65 adenomas (90.3%), 2 cancers (2.6%), 3 traditional serrated adenomas (4.1%), and 2 hyperplastic polyps (2.8%). Boston Bowel Preparation Scale Segment Scores (BBPS-SS) were 3 in 50 cases, 2 in 21 cases, and 1 in 1 case.
Median ΔE values in the underwater group were 10.0 (WLI), 15.7 (BLI), and 11.7 (LCI), while those in the under-gel group were 12.4 (WLI), 21.1 (BLI), and 13.1 (LCI). ΔE was significantly higher in the under-gel group than the underwater group under WLI and BLI (p = 0.01 and p < 0.01, respectively).
In subgroup analysis by BBPS-SS, under-gel observation showed significantly higher ΔE in WLI and BLI when BBPS-SS ≤2 (p = 0.03 and p < 0.01, respectively). No significant differences were seen when BBPS-SS was 3.

Conclusion

Under-gel observation improved the visibility of lesion margins under WLI and BLI compared to underwater observation, particularly in patients with suboptimal bowel preparation. Gel immersion endoscopy may therefore be a useful adjunct in difficult visualization conditions during colorectal UEMR.