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

Area of Science:

• Radiology
• Oncology
• Medical Imaging

Background:

• Accurate nodal staging is crucial for treatment decisions in early rectal cancer.
• Current MRI methods for nodal staging have limitations, representing a knowledge gap.

Purpose of the Study:

• To evaluate the predictive performance of quantitative diffusion-weighted imaging (DWI) and qualitative T2-weighted imaging (T2WI) parameters for lymph node involvement in early rectal cancer.
• To compare the diagnostic utility of DWI-derived apparent diffusion coefficient (ADC) values versus T2WI-based criteria.

Main Methods:

• Retrospective analysis of rectal MRI scans from patients with clinical early rectal cancer (T1-T2) who underwent total mesorectal excision without neoadjuvant therapy.
• Segmentation of mesorectal lymph nodes on DWI for ADC value extraction by a junior reader.
• Independent assessment of qualitative T2WI parameters (e.g., size, morphology) of suspicious lymph nodes by junior and senior readers.
• Histopathology served as the reference standard for lymph node status (pN+ vs. pN-).

Main Results:

• No significant difference in mean ADC values was observed between metastatic (pN+) and benign (pN-) lymph nodes.
• The Dutch criteria, combining T2WI size and morphologic parameters, demonstrated superior diagnostic performance compared to the quantitative DWI ADC parameter.
• The senior reader using the Dutch criteria achieved higher accuracy (79.7%), sensitivity (56.5%), specificity (91.3%), positive predictive value (PPV) (76.5%), and negative predictive value (NPV) (80.8%) compared to the junior reader.

Conclusions:

• Qualitative T2WI parameters, particularly when assessed using the Dutch criteria, are more effective than quantitative DWI ADC values in differentiating metastatic from benign lymph nodes in early rectal cancer.
• The findings underscore the need for further investigation into novel and more objective imaging techniques for lymph node characterization in rectal cancer staging.