Colorectal cancer is the most common malignant tumor of the digestive tract. At present, surgery is still the main treatment for rectal cancer. Although stapler anastomosis improves the safety of surgical resection and reconstruction for middle and low rectal cancer, surgical complications, especially anastomotic leakage, are inevitable, especially for middle and low rectal cancer, where the incidence of anastomotic leakage reaches 8-11%. The outcome of anastomotic leakage will lead to anastomotic stenosis, especially in middle and low rectal cancer after neoadjuvant radiotherapy, and the incidence of anastomotic stenosis is as high as 3%-10%. Previous studies have suggested that anastomotic diameter \< 20mm is considered as an anastomotic stenosis, and it has also been shown that an anastomotic diameter less than 1/3 of the original diameter of the intestinal lumen is considered as an anastomotic stenosis. Anastomotic stenosis can not only cause intestinal obstruction symptoms, such as abdominal distension and abdominal pain, but also be accompanied by frequent defecation, which affects the quality of life, and many patients face the outcome of permanent stoma or temporary stoma again.

Anastomotic stenosis is divided into membranous stenosis and tubular stenosis according to the degree of stenosis. For anastomotic membranous stenosis, endoscopic incision of the stenosis ring or balloon dilatation is the preferred method for the treatment of membranous stenosis. However, endoscopic scar incision and balloon dilation require repeated, multiple treatments to achieve long-term effectiveness, with the risk of perforation, pelvic infection, and bleeding. Balloon dilatation or scar incision has little effect on patients with low anastomosis position or tubular stenosis, and nearly 30% of patients need to undergo resection and reconstruction of the stenotic anastomosis. As anastomotic stenosis is often caused by anastomotic leakage, anastomotic ischemia, radiotherapy and chemotherapy, use of stapler, pelvic infection and low anastomosis, the anatomical structure is unclear, the scar around the bowel is dense, and complications such as ureteral and urethral injury and massive bleeding of presacral veins are more likely to occur during the resection and reconstruction of the stricture. Lefevre et al. reported 33 patients who underwent resection and reconstruction of transabdominal rectal anastomotic stenosis, and the incidence of perioperative complications was 54.5%, including anastomotic leakage of 18%（6/33） and postoperative intestinal obstruction of 12%. Genser et al. reported 50 patients with surgical treatment of anastomotic stenosis, of whom 12（24%） received intraoperative blood transfusion, with an average blood transfusion volume of 2.5 units. The incidence of intraoperative complications was 12%, including 5 cases of bladder injury and 1 case of splenectomy due to splenic injury due to unclear anatomical location. Westerduin et al. summarized 59 patients who underwent secondary surgery for anastomotic leakage and stenosis, and 41% of them had recurrent anastomotic leakage 14 months after surgery. During the follow-up of 27 months, only 66% of the patients regained intestinal continuity,24%of the patients received permanent colostomy, and 10% of the patients retained ileostomy.

Due to the difficulty of surgery, it is difficult to remove the scar tissue around the anastomosis in the traditional abdominal resection and reconstruction surgery. The new rectorectum cannot be pulled out and anastomosed with the distal rectoanal canal again. After reluctant anastomosis, the incidence of anastomotic leakage is still high due to the high tension of rectorectum, and many patients have to accept permanent stoma. Transanal total mesorectal excision (taTME), which uses a transanal approach to perform total mesorectal excision, has been demonstrated by our team for the surgical treatment of middle and low rectal cancer with difficult pelvis. However, the use of taTME in the treatment of anastomotic stenosis is rarely explored at present. Our team first reported this surgical method in 2021. The investigators retrospectively summarized 17 patients who underwent resection and reconstruction of anastomotic stenosis by transabdominal transanal endoscopic surgery. The ileostomy or colostomy was closed in 15 patients, which proved the safety and effectiveness of this surgical method. Transabdominal transanal endoscopic resection and reconstruction surgery has obvious advantages in the treatment of patients with rectal anastomotic stenosis. First, it can accurately separate the narrow distal intestine, and transanal anastomosis of the substitute rectum and the distal rectoanal canal can be performed, which reduces the difficulty of reconstruction. Secondly, from the distal normal anorectal canal, it can enter the normal anatomical structure space, and the narrow scar segment can be completely resected by endoscopic magnification. At the same time, it can reduce the accidental injury of the surrounding normal tissue and significantly reduce the incidence of intraoperative complications. Finally, the mobilization of the left hemicolon and splenic flexure of the abdomen was completed laparoscopically, and the specimen was removed through the anus, which did not require additional abdominal incision and thus reduced trauma. Although the advantages of transanal transabdominal combined with laparoscopic resection and reconstruction in the treatment of severe rectal anastomotic stenosis are very obvious in theory and preliminary clinical practice, there is a lack of prospective studies.

For the above reasons, the investigators plan to conduct a prospective clinical study to observe the safety and efficacy of transanal laparoscopic resection and reconstruction in patients with rectal anastomotic stenosis, in order to improve the quality of life of patients with rectal anastomotic stenosis, and to provide high-level evidence-based medical basis for the selection of resection and reconstruction surgery for patients with rectal anastomotic stenosis.