Evaluation of MRI characterisation of histopathologically matched lymph nodes and other mesorectal nodal structures in rectal cancer.

Purpose: To evaluate current MRI-based criteria for malignancy in mesorectal nodal structures in rectal cancer.

Method: Mesorectal nodal structures identified on baseline MRI as lymph nodes were anatomically compared to their corresponding structures histopathologically, reported as lymph nodes, tumour deposits or extramural venous invasion. All anatomically matched nodal structures from patients with primary surgery and all malignant nodal structures from patients with neoadjuvant treatment were included. Mixed-effects logistic regression models were used to evaluate the morphological criteria irregular margin, round shape, heterogeneous signal and nodal size, as well as the combined 2016 European Society of Gastrointestinal and Abdominal Radiology (ESGAR) consensus criteria, with histopathological nodal status as the gold standard.

Results: In total, 458 matched nodal structures were included from 46 patients (mean age, 67.7 years ± 1.5 [SD], 27 men), of which 19 received neoadjuvant treatment. The strongest associations in the univariable model were found for short-axis diameter ≥ 5 mm (OR 21.43; 95% CI: 4.13-111.29, p < 0.001) and heterogeneous signal (OR 9.02; 95% CI: 1.33-61.08, p = 0.024). Only size remained significant in multivariable analysis (OR 12.32; 95% CI: 2.03-74.57, p = 0.006). When applying the ESGAR consensus criteria to create a binary classification of nodal status, the OR of malignant outcome for nodes with positive ESGAR was 8.23 (95% CI: 2.15-31.50, p = 0.002), with corresponding sensitivity and specificity of 54% and 85%, respectively.

Conclusion: The results confirm the role of morphological and size criteria in predicting lymph node metastases. However, the current criteria might not be accurate enough for nodal staging.

Key Points: Question Pretreatment lymph node staging in rectal cancer is challenging, and the ESGAR consensus criteria are not fully validated. Findings Although the ESGAR criteria correlated with malignant outcomes, diagnostic performance in terms of particular sensitivity, but also specificity, was not high. Clinical relevance Accurate nodal staging in rectal cancer is crucial for individual treatment planning. However, this validation of the current ESGAR consensus criteria suggests that these should be used with caution.