Extramural vascular invasion (EMVI) is the direct invasion of a blood vessel (usually a vein) by a tumor. 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. mrEMVI is seen as tubular or serpiginous projections of intermediate or hypointense signal intensity on T2WI, which follow the course of a perirectal vein and may be either directly contiguous with the tumor or non-contiguous.
The mrEMVI score is a five-point grading system that is derived by comparing the morphological features in MRI with histopathological references. It is used to evaluate the severity of vascular invasion. The scoring system ranges from 0 to 4 (0-2 is mrEMVI negative and 3-4 is mrEMVI positive).
Treatment and prognosis
The presence of EMVI on pre-treatment MRI has been associated with a four-fold increase in the risk of distant metastases, and a significant reduction in disease-free survival, from 74% to only 35% 3.
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