Abstract:Objective To evaluate the efficacy and safety of self‑expanding metallic stent (SEMS) placement guided by ultra‑fine endoscope for malignant colorectal obstruction. Methods Data of 107 patients with malignant colorectal obstruction treated by colorectal SEMS implantation under endoscopy in Peking University Third Hospital from January 2018 to October 2022 were retrospectively analyzed. According to the type of endoscope, patients were divided into the conventional colonoscope group (n=80) and the ultra‑fine endoscope group (n=27). Lesion location, the best location of lesion at the screen, the time of inserting guidewire, the time of overall operation and complication incidence were compared. The independent variables with P <0.2 and some special clinical and imaging features were included in the binary logistic regression for multivariate analysis to determine the influencing factors for using ultra‑fine endoscope. Results The rectosigmoid obstruction in the ultra‑fine group was significantly higher than that in the conventional group [74.1% (20/27) VS 46.3% (37/80)]. More patients in the ultra‑fine endoscopy group had abdominal lymph nodes and distant metastasis [88.9% (24/27) VS 67.5% (54/80)]. There was significant difference in the best location of lesion at the screen (χ2=4.14,P=0.042). The time of inserting the guidewire in the ultra‑fine group was significantly shorter than that in the conventional group [4.0 (2.0, 7.0) min VS 8.5 (5.0, 14.3) min, Z=-3.22, P=0.001]. However, there was no significant difference in the overall operation time (28.3±12.6 min VS 23.4±11.5 min, t=-1.79, P=0.077). Two stent placements failed in the conventional group and all stent placements succeeded in the ultra‑fine endoscope group. There was no severe complication such as hemorrhage or acute peritonitis caused by perforation in either group. Logistic regression analysis showed that the presence of distant metastasis (OR=6.775, 95%CI: 1.084‑42.346, P=0.041) and narrow lumen located at the outside 1/2 of the screen (OR=3.097, 95%CI: 1.406‑6.822, P=0.005) were influencing factors for the usage of ultra‑fine endoscopy. On the other hand, ultra‑fine endoscopy was not recommended for patients with lesions located at the descending colon (descending colon VS rectosigmoid: OR=0.073, 95%CI:0.009‑0.602, P=0.015). Conclusion Ultra‑fine endoscopy can significantly shorten the time of guidewire insertion and improve the success rate of SEMS placement, especially for those with abdominal lymph node and distant metastasis, and whose narrow lumen located at the outside 1/2 of the screen. Ultra‑fine endoscopy is not recommended for patients with lesions located at the descending colon.