Comparison of Diagnostic Performance of Node-RADS and ESGAR Criteria in Rectal Cancer Nodal Assessment at MRI.

Background Suboptimal nodal assessment in rectal cancer hampers pre- and postoperative assessment for treatment planning. A recently proposed standardized nodal evaluation system, Node Reporting and Data System 1.0 (Node-RADS), lacks robust evidence of diagnostic utility. Purpose To validate and optimize Node-RADS against European Society of Gastrointestinal and Abdominal Radiology (ESGAR) criteria in MRI-based nodal assessment in patients with rectal cancer, with subsequent patient-level external validation. Materials and Methods This retrospective study included consecutive patients with rectal cancer who underwent MRI and radical surgery between January 2016 and July 2025. Node-level analyses were performed in patients from center 1, and external patient-level validation was performed in patients from centers 2 and 3. Two radiologists independently evaluated mesorectal nodes according to Node-RADS and ESGAR criteria. The optimal threshold of the Node-RADS score for diagnosing malignancy was determined using the Youden index. Diagnostic performance and interobserver agreement were assessed using area under the receiver operating characteristic curve (AUC) and Cohen κ, respectively. Results This study included 780 patients (median age, 61 years [IQR, 53-68 years]; 477 men). Among 251 patients (1302 nodes) who underwent direct surgery, the optimal threshold of Node-RADS score was 3 or higher (Youden index, 0.65), enabling simplification to a modified model, the Simplified Nodal Assessment Process in Rectal Cancer (recSNAP). recSNAP outperformed the ESGAR criteria at both the node level (AUC, 0.83 vs 0.71; P < .001) and the patient level (AUC, 0.83 vs 0.71; P < .001). Similarly, among 284 patients (918 nodes) who received neoadjuvant chemoradiotherapy before surgery, Node-RADS with a threshold of 4 or higher outperformed the ESGAR criteria (AUC, 0.72 vs 0.66; P < .001). Interobserver agreement for Node-RADS at pre- and posttreatment MRI was substantial (Cohen κ, 0.76 and 0.64, respectively). Conclusion Node-RADS outperformed the ESGAR criteria for MRI-based rectal adenocarcinoma nodal assessment at both the node and patient levels and in external validation, and a simplified version of Node-RADS exhibited similar diagnostic performance. © RSNA, 2026 Supplemental material is available for this article.