Patients with rectal or rectosigmoid cancer undergoing radical resection will be randomly assigned to either high-tie (HT) or low-tie (LT) ligation of the Inferior Mesenteric Artery (IMA). Proximal bowel blood perfusion will be measured using Laser Speckle Contrast Imaging, and the perfusion characteristics will be compared between the two ligation groups.

Additionally, for participants randomized to the LT group, an embedded prospective cohort sub-study will be performed. This sub-study involves controlled, temporary intraoperative occlusion of the preserved Left Colic Artery (LCA). During this temporary occlusion, LSCI will be used to assess the resulting changes in colonic perfusion, specifically measuring outcomes like the ischemic demarcation line (LOD) retraction distance, to further investigate the functional contribution of the preserved LCA. The overall trial aims to determine the optimal IMA ligation strategy based on objective perfusion data and a deeper understanding of LCA's role.

The primary goal of this clinical trial is to compare proximal bowel blood perfusion following HT versus LT of the IMA during anterior resection for rectal cancer. LSCI will be used to assess perfusion in both groups.Additionally, this trial incorporates an embedded prospective cohort sub-study, which will be conducted specifically within the LT group, where the Left Colic Artery (LCA) is preserved. The purpose of this sub-study is to further elucidate the impact of this LCA preservation on left colonic perfusion in these patients. This will be achieved by investigating the retraction distance of the ischemic demarcation line following temporary occlusion of the preserved LCA under LSCI guidance, and by exploring potential anatomical and pathophysiological factors that may contribute to variations in this retraction distance.

The main questions the study seeks to answer are:

Does HT ligation result in significantly different proximal bowel blood perfusion, as measured by LSCI, compared to LT ligation? Does knowledge of intraoperative bowel perfusion, as assessed by LSCI, influence surgical decision-making, specifically regarding changes to the planned transection line? Are there significant differences in quantified perfusion intensity at the transection line between HT and LT ligation techniques? What is the retraction distance of the ischemic demarcation line, observed via LSCI, following temporary occlusion of the LCA, and what are the potential anatomical or pathophysiological factors associated with variations in this distance? Patients undergoing anterior resection for rectal cancer will be randomized to receive either HT or LT ligation of the IMA. LSCI will be used intraoperatively to assess bowel perfusion.

Participants will:

Undergo anterior resection for either rectal or rectosigmoid cancer, with HT or LT ligation of the IMA determined by the randomization process.

Have bowel perfusion assessed intraoperatively using LSCI. Have the maximum perfusion distance (MPD) measured as the primary outcome for the main randomized trial component.

Have the perfusion intensity at the transection line quantified as a secondary outcome.

Have any changes to the planned transection line documented based on intraoperative LSCI findings, as a secondary outcome.

As part of the embedded prospective cohort sub-study, undergo temporary intraoperative occlusion of the LCA with subsequent LSCI assessment to measure the retraction distance of the ischemic demarcation line.

As part of the embedded prospective cohort sub-study, have data collected on relevant potential anatomical (e.g., vascular anatomy variations) and pathophysiological factors (e.g., presence of atherosclerosis, patient comorbidities) that may influence the ischemic demarcation line retraction distance.

This trial aims to provide high-level evidence to inform and optimize IMA management strategies during anterior resection for rectal or rectosigmoid cancer, based on proximal bowel perfusion assessment using LSCI visualization, and to provide deeper mechanistic insights into the specific role and functional importance of the LCA in maintaining colonic perfusion.

Inclusion Criteria:

1. a confirmed diagnosis based on pathological reports;
2. patients who had not received any prior treatment;

Exclusion Criteria:

1. a history of previous abdominal surgery or neoadjuvant chemotherapy/radiation affecting bowel perfusion or anastomosis;
2. patients requiring emergency surgery due to acute complications;
3. intraoperative findings necessitating a shift to alternative procedures, such as local excision, abdominoperineal resection, Hartmann's operation, or intersphincteric resection.

All data generated in this study will be made available in the main publication or its supplementary materials. Additional de-identified datasets will be shared upon reasonable request from qualified researchers after completion of the study and approval by the institutional ethics committee.

Individual participant data (IPD) and supporting documents will be available beginning 6 months after publication of the study results and will remain available for a period of 3 years.

Qualified researchers affiliated with academic institutions, hospitals, or research organizations may request access to the de-identified individual participant data (IPD), study protocol, and statistical analysis plan. Data will be shared for research purposes only, following submission and approval of a research proposal and data access agreement.

The study employs single-blinding where patients are unaware of their treatment allocation (High Tie [HT] or Low Tie [LT]). The operating surgeon is necessarily unblinded intraoperatively to perform the assigned surgical technique. The statistician(s) performing the data analysis will be masked to treatment group assignments until the analysis is complete. Randomization is managed by a designated investigator using pre-generated random numbers after eligibility confirmation (1:1 ratio to HT or LT group).