MRI Morphological Features for Assessing Lymph Node Restaging in Rectal Cancer After Neoadjuvant Chemoradiotherapy.

Rationale and objectives: Accurate lymph node (LN) restaging after neoadjuvant chemoradiotherapy (nCRT) is critical for guiding subsequent treatment decisions in patients with rectal cancer. The currently recommended European Society of Gastrointestinal and Abdominal Radiology (ESGAR) method has shown limited accuracy. This study aimed to evaluate the diagnostic performance of specific MRI morphological features for LN restaging post-nCRT and to develop a reliable, clinically applicable imaging-based assessment method.

Materials and methods: In this retrospective multi-center study, one training cohort and two external validation cohorts were included. MRI morphological features were assessed for their association with pathological LN status using χ² tests and multivariable logistic regression. Diagnostic performance was evaluated using the area under the receiver operating characteristic curve (AUC). Interobserver agreement was evaluated using Cohen κ coefficient and the intraclass correlation coefficient (ICC [1,1]).

Results: Among 238 patients in the training cohort, 64 (26%) had pathologically confirmed positive LNs. Multivariate analysis revealed that signal homogeneity (odds ratio [OR], 3.23; P=.02), interruption of vessels (OR, 6.97; P=.001), and tail sign (OR, 4.02; P=.002) were independent predictors of positive LN status. The developed "Three-features method" (positive if any two features were present) achieved an AUC of 0.83, with 69% sensitivity, 86% specificity, and 82% overall accuracy-significantly outperforming the ESGAR method (AUC=0.68). External validation showed consistent diagnostic performance (AUC=0.74 and 0.77).

Conclusion: The integration of signal homogeneity, interruption of vessels, and tail sign into a combined MRI-based "Three-features method" significantly improves the accuracy of LN restaging after nCRT compared to ESGAR method.