Diffusion-weighted imaging increases the diagnostic performance of magnetic resonance imaging in assessing rectal cancer T stage and reduces intra- and interobserver variability.

Background: Accurate preoperative staging is pivotal in guiding rectal cancer treatment, and in particular for selecting appropriate neoadjuvant therapies and surgical approaches. Magnetic resonance imaging (MRI) remains the standard modality for local staging. However, it has some limitations, particularly in tumors at intermediate clinical stages. Recent evidence has shown that incorporating diffusion-weighted imaging (DWI) can improve diagnostic performance, although its role in T staging has not been completely elucidated. Methods: The diagnostic performance of conventional MRI alone vs. MRI plus DWI in rectal cancer staging was retrospectively evaluated. The correlation between preoperative MRI findings and postoperative histopathological staging was examined. Intra- and interobserver agreement among radiologists with various levels of experience were assessed, both with and without DWI. Results: DWI-MRI improved staging accuracy, particularly for T2 and T3 tumors. The sensitivity and specificity for T2 staging increased from 68% and 96% (MRI alone) to 91% and 98% (DWI-MRI), respectively, while the sensitivity and specificity for T3 staging improved from 91% to 97%, and from 78% to 92%, respectively. The intraobserver agreement increased from 90.60% to 94.02% in experienced readers, and from 81.2% to 87.18% in less experienced ones. The interobserver agreement for DWI-MRI increased from 83.76% to 88.03%. Conclusions: DWI-MRI can enhance the accuracy of rectal cancer T staging, particularly when assessing rectal wall invasion, and it reduces overstaging. Moreover, it improves diagnostic consistency among radiologists, regardless of experience. Hence, the routine integration of DWI into preoperative MRI protocols can optimize clinical decision-making and treatment planning.