Extramural vascular invasion (EMVI) is the direct invasion of a blood vessel (usually a vein) by a tumour. In rectal cancer, this can occur on a macroscopic level and be detected on staging MRI. It is a significant prognostic factor, being a predictor of haematogenous spread.
Rectal MRI is considered highly specific and moderately sensitive tool in the detection of EMVI. EMVI is seen as tubular or serpiginous projections of intermediate signal intensity, which follow the course of a perirectal vein and may be either directly contiguous with the tumour or non-contiguous.
Treatment and prognosis
The presence of EMVI on pre-treatment MRI has been associated with a four-fold increase in risk of distant metastases, and a significant reduction in disease-free survival, from 74% to only 35% 3.
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