Preoperative Nasal Intestinal Obstruction Catheter Mediated Terminal Ileum Fecal Diversion Versus Intraoperative Protective Ileostomy for Preventing Anastomotic Leakage After Mid Low Rectal Cancer Surgery: A Non Inferiority, Prospective, Multicenter Randomized Controlled Trial

Inclusion Criteria: I01. Aged ≥18 years, capable of understanding the study and providing written informed consent. I02. Rectal adenocarcinoma confirmed by colonoscopic biopsy. I03. The distal margin of the tumor is ≤5 cm from the anal verge as assessed by pelvic MRI, digital rectal examination and/or endoscopy; this cutoff may be extended to ≤7 cm for male patients and/or those with BMI ≥28 kg/m². I04. Treatment pathway is consistent with current guidelines and confirmed in writing by the multidisciplinary team (MDT): Patients proceeding directly to surgery without neoadjuvant therapy must be cT1-2N0, or low-risk cT3a/bN0 on pelvic MRI, with the mesorectal fascia (MRF) ≥2 mm from the tumor, negative MRI-detected extramural venous invasion (mrEMVI), no suspicious lateral lymph nodes, and no levator ani muscle/sphincter involvement. Patients who have previously received neoadjuvant systemic chemotherapy without pelvic radiotherapy in accordance with guidelines may be enrolled; such treatment decision must have been made prior to study recruitment, and the MDT shall document in writing the rationale for proceeding directly to surgery\[29,30\]. I05. Planned open, laparoscopic or robot-assisted Dixon operation with primary anastomosis. I06. The attending physician judges, prior to randomization, that protective fecal diversion is indicated per current clinical practice. I07. Eastern Cooperative Oncology Group (ECOG) performance status 0-2; organ function and coagulation status are tolerable for the planned surgery. I08. Willingness to undergo randomization, scheduled anastomotic assessment, and a minimum of 6-month follow-up. Exclusion Criteria: E01. Emergency surgery, or presence of complete bowel obstruction requiring urgent management, bowel perforation, or uncontrolled gastrointestinal bleeding. E02. Prior pelvic radiotherapy; or high-risk features that mandate neoadjuvant therapy per current guidelines in patients without neoadjuvant treatment, including cT3c/d, cT4, N2, threatened/positive MRF, positive mrEMVI, suspicious lateral lymph nodes, or levator ani muscle/sphincter involvement; or intended to bypass indicated neoadjuvant therapy for the purpose of participating in this study. E03. Imaging or preoperative assessment indicating primary anastomosis is not feasible; planned Miles operation, Hartmann procedure, or total colectomy/proctectomy. E04. Clinical M1 disease, or other conditions requiring major concurrent surgery that substantially alters perioperative risk. E05. Prior esophageal, gastric or complex abdominal surgery, severe adhesions, upper gastrointestinal stricture, or other conditions rendering transnasal long-tube placement unacceptably risky. E06. Severe nasal/nasopharyngeal disease, risk of skull base fracture, active upper gastrointestinal bleeding, or other contraindications to transnasal intubation. E07. Uncorrected severe cardiac, pulmonary, hepatic, renal insufficiency or coagulopathy. E08. Pregnancy or lactation; women of child-bearing potential unable to complete pregnancy exclusion as clinically required. E09. Known severe allergy to catheter materials or planned contrast agents with no acceptable alternative. E10. Severe psychiatric, cognitive or communication impairment without legal representative available, precluding understanding of the study or compliance with key safety measures. E11. Participation in another interventional study within 30 days prior to screening that may confound study endpoints. E12. Investigator judges the subject unsuitable for inclusion for specific safety reasons, with documentation in the screening record.