Lymph nodes in MRI-based early-stage rectal cancer: can MRI accurately predict lymph node involvement?

To investigate whether quantitative DWI and qualitative T2WI parameters can predict lymph node involvement in clinical early rectal cancer.

This retrospective study included consecutive patients who had rectal MRI from January 1, 2010, to March 31, 2021, showing T1-T2 rectal cancer before undergoing total mesorectal excision without neoadjuvant therapy. Visible mesorectal lymph nodes on DWI were segmented by a junior reader, and ADC values were extracted. Additionally, the junior reader and a senior reader independently recorded qualitative T2WI parameters of the most suspicious lymph node per patient. Histopathology was the reference standard for malignant (pN+) and benign (pN-) lymph node status.

Of 69 patients (37 men and 32 women) (median age, 55 years; IQR: 48-66), 23 (33%) had pN+ status; 46 (67%) had pN- status. ADC_mean (in × 10^-3 mm²/s) of the most suspicious lymph node was not different between the two patient groups (junior reader: 1087 vs. 926, p = 0.31; senior reader: 1178 vs. 1086, p = 0.89). The Dutch criteria, based on the combination of T2WI size and morphologic parameters, showed better diagnostic performance for the senior vs. junior reader: accuracy, sensitivity, specificity, PPV, and NPV of 79.7% (95% CI: 68.3-88.4%), 56.5% (95% CI: 34.5-76.8%), 91.3% (95% CI: 79.2-97.6%), 76.5% (95% CI: 50.1-93.2%), and 80.8% (95% CI: 67.5-90.4%), vs. 69.6% (95% CI: 57.3-80.1%), 26.1% (95% CI: 12.2-48.4%), 91.3% (95% CI: 79.2-97.6%), 60% (95% CI: 26.2-97.8%), and 71.2% (95% CI: 57.9-82.2%).

Additional research on alternative and more objective methods for lymph node characterization is needed.

Question The performance of MRI for nodal staging in clinical early rectal cancer in particular is a knowledge gap in the literature. Findings The Dutch criteria, based on T2WI size and morphologic parameters, performed better in differentiating metastatic from benign lymph nodes than the quantitative DWI ADC parameter. Clinical relevance Accurate nodal staging in early rectal cancer is crucial for treatment decision-making. Our study highlights the need for additional research on alternative and more objective methods for lymph node characterization.