Extramural vascular invasion (EMVI)

Extramural vascular invasion (EMVI) is the direct invasion of a blood vessel (usually a vein) by a tumour. In colorectal cancer, this can occur on a macroscopic level and be detected on staging MRI (mrEMVI) and/or CT ^1-6. It is a significant prognostic factor, being a predictor of haematogenous spread. 

Radiographic features

CT

EMVI is characterised by having at least one of the following features present ⁶:

• serpentine primary tumour extension within an irregular distorted vein

• focal or persistent peri-tumoural vein calibre change (may be seen as mural irregularity)

• obvious tumour/tumour thrombus in draining veins

MRI

MRI is considered a highly specific and moderately sensitive tool in the detection of EMVI ^ref. mrEMVI is seen as tubular or serpiginous projections of intermediate or hypointense signal intensity on T2WI, which follow the course of a pericolonic/perirectal vein and may be either directly contiguous with the tumour or non-contiguous. Tumour deposits (mrTD) may be found in association with EMVI, along the path of vessels, and seen to interrupt their course.

mrEMVI Score

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.

See also

• rectal cancer staging

• approach to rectal MRI

• rectal cancer response assessment

• terminology of rectal cancer staging