MRI assessment of extramural venous invasion in rectal cancer: a practical pictorial review.

Abstract

Extramural venous invasion (EMVI), the spread of rectal tumor cells into veins beyond the muscularis propria, is one of the most prognostically powerful preoperative findings detectable on pelvic magnetic resonance imaging (MRI). Meta-analytic evidence indicates that baseline mrEMVI is associated with an approximately fourfold increased risk of metachronous metastases (OR 3.91; 95% CI 2.61-5.86), and it independently predicts inferior disease-free and overall survival. Despite this evidence, MRI-based EMVI assessment remains inconsistently applied in routine practice. This pictorial review provides a structured, image-focused approach to MRI-detected EMVI, covering the technical requirements for reliable detection, relevant venous anatomy, imaging hallmarks on high-resolution T2-weighted and diffusion-weighted imaging, the validated five-point grading scale, the most clinically significant mimics and pitfalls, and the specific challenges of restaging after neoadjuvant therapy. We also summarize the clinical implications of EMVI grading for treatment intensification, lateral lymph node management, and organ-preservation decisions. Graded MRI assessment of EMVI provides clinically meaningful prognostic information beyond binary positive/negative reporting and is increasingly used to inform multidisciplinary decisions in rectal cancer, although evidence that grade-directed treatment modification improves outcomes remains limited. Reproducible interpretation requires attention to key pitfalls, including equivocal grade 2 findings, small-caliber vessels, and reduced diagnostic reliability after neoadjuvant therapy.