This study aims to identify risk factors-including clinical and imaging indicators such as middle rectal artery (MRA) diameter-that may be associated with lateral lymph node metastasis (LLNM) in rectal cancer located below the peritoneal reflection, and to construct a corresponding predictive model.The main questions it aims to answer are:

What factors are associated with clinically suspected lateral lymph node metastasis in rectal cancer below the peritoneal reflection? Can an effective predictive model be constructed based on these factors? Participants' clinical information has been collected for statistical analysis.

Objective: This study aimed to investigate the risk factors for suspected lateral lymph node metastasis in rectal cancer below the peritoneal reflection and to construct a predictive model.

Methods: This retrospective study analyzed data from 690 patients with rectal cancer below the peritoneal reflection who were treated at the First Affiliated Hospital of Fujian Medical University between January 2022 and December 2024. The original dataset was randomly divided into a training set and validation set at a ratio of 7:3. Univariate and multivariate logistic regression analyses were performed on the training set to identify the risk factors associated with clinical lateral lymph node (cLLN) metastasis and to construct a predictive model.

Inclusion Criteria:

• Age at diagnosis between 18 and 75 years
• Pathological confirmation of rectal adenocarcinoma by endoscopic biopsy
• Imaging confirmation that the tumor was located below the peritoneal reflection
• Availability of rectal MRI scans providing detailed imaging of the pelvic region
• Received treatment at The First Affiliated Hospital of Fujian Medical University between January 2022 and December 2024

Exclusion Criteria:

• Pathological diagnosis of non-primary rectal malignancies
• Previous treatment for rectal cancer with chemotherapy, radiotherapy, or surgery, with the current presentation indicating recurrence
• Incomplete rectal MRI data or poor image quality affecting interpretation
• Incomplete medical or clinical records. Ultimately, 690 patients were included in the final analysis

This retrospective cohort study included adult patients (aged 18-75 years) with pathologically confirmed rectal adenocarcinoma located below the peritoneal reflection, who had complete preoperative pelvic MRI data and were treated at The First Affiliated Hospital of Fujian Medical University between 2022 and 2024. The study aimed to analyze this population to identify risk factors and develop a predictive model for clinically suspected lateral lymph node metastasis.

Individual participant data that underlie the results reported in the article, after deidentification, will be made available upon reasonable request to the corresponding author, after article publication.

Data and supporting documents will become available upon reasonable request after the publication of the study.

Researchers who provide a methodologically sound proposal may request access to deidentified individual participant data and supporting documents. Proposals should be directed to the corresponding author at 13600801413@139.com. To gain access, requestors will need to sign a data access agreement. Approval is subject to review by the study's principal investigator and the institutional ethics committee.