Contrast-enhanced vs T2-weighted MRI for mesorectal nodal staging in rectal cancer

To compare the diagnostic performance of the "Avocado Sign", a contrast-enhanced MRI feature, with T2-weighted morphological criteria for predicting mesorectal lymph node involvement in rectal cancer.

This retrospective single-centre study included 120 consecutive patients with histopathologically confirmed rectal cancer who underwent 3-T pelvic MRI between January 2020 and May 2025. Two blinded abdominal radiologists independently assessed the Avocado Sign on fat-suppressed contrast-enhanced T1-weighted images and, in a separate session, T2-weighted morphological features for all mesorectal lymph nodes. The reference standard was total mesorectal excision histopathology. Performance was evaluated against European Society of Gastrointestinal and Abdominal Radiology (ESGAR) consensus criteria, literature-derived criteria, and a cross-validated cohort-optimised T2 parameter combination. Areas under the receiver operating characteristic curve (AUC) were compared using DeLong tests.

In total, 120 patients (89 men, 31 women; median age 65 years [IQR 58-73]) were evaluated. Mesorectal nodal metastases were confirmed in 56 (46.7%) patients. The Avocado Sign achieved an AUC of 0.91 (95% confidence interval [CI]: 0.86-0.96), with sensitivity of 94.6% (53/56) and specificity of 87.5% (56/64). It significantly outperformed the ESGAR consensus criteria (AUC 0.72; 95% CI: 0.64-0.81; p < 0.001) and the cohort-optimised T2 parameter combination (apparent AUC 0.81, cross-validated AUC 0.79; p = 0.02). All literature-derived T2 criteria demonstrated lower performance (AUC 0.58-0.78).

The contrast-enhanced Avocado Sign provided superior discrimination of mesorectal nodal status compared with comprehensive T2-weighted MRI criteria, supporting routine inclusion of fat-suppressed contrast-enhanced T1-weighted sequences in rectal cancer staging protocols.

QuestionCan contrast-enhanced MRI improve mesorectal lymph node staging accuracy compared with established T2-weighted morphological criteria in patients with rectal cancer? FindingsThe Avocado Sign demonstrated significantly superior diagnostic performance (area under the curve 0.91) compared with European consensus criteria (0.72) and all tested T2-weighted approaches. Clinical relevanceIncorporating contrast-enhanced sequences into rectal MRI protocols substantially improves nodal staging accuracy, supporting refined treatment selection for neoadjuvant therapy and organ-preservation strategies.