A head-to-head comparison of MRI and CT using Node-RADS for rectal cancer lymph nodes: Observer agreement and diagnostic performance

Purpose: To compare the assessment agreement and diagnostic performance of CT and MRI using the Node Reporting and Data System (Node-RADS) for preoperative regional lymph node metastasis (LNM) in rectal cancer.Methods: This retrospective study included 97 rectal adenocarcinoma patients who underwent preoperative contrast-enhanced CT and MRI.A total of 148 lymph nodes (LNs) were evaluated.Postoperative histopathology served as the reference standard.CT-based and MRI-based Node-RADS scores, as well as the ESGAR category, were assessed.Diagnostic performance was evaluated by receiver operating characteristic (ROC) curve analysis, including area under the curve (AUC), sensitivity, and specificity.Inter-and intra-observer agreement for Node-RADS was evaluated using weighted kappa statistics.A subgroup analysis was further conducted on 27 imagepathology matched LNs.Results: Node-RADS scores showed a strong positive correlation with pathological N stage (MRI: r = 0.724; CT: r = 0.654; both p < 0.01).MRI-based Node-RADS achieved the highest diagnostic performance (AUC = 0.883), which was significantly higher than CT-based Node-RADS and the ESGAR .Inter-reader agreement for Node-RADS was good to excellent for both modalities, and was higher for MRI ( = 0.921) than CT ( = 0.785).For small LNs (<5 mm in short axis diameter), MRI-based Node-RADS demonstrated a higher AUC than CT-based Node-RADS (0.895 vs. 0.760).In the imaging-pathology matched subgroup, MRI-based Node-RADS (AUC = 0.793) also outperformed CT-based Node-RADS (AUC = 0.712). Conclusion:Node-RADS provides a standardized tool for preoperative regional lymph node assessment in rectal cancer, showing better diagnostic performance than ESGAR criteria.MRI demonstrates higher diagnostic performance and inter-observer agreement than CT, supporting MRI as the preferred modality.