Extramural Vascular Invasion (EMVI)
Definition
EMVI is the presence of tumor cells within vessels beyond the muscularis propria of the rectum. At MRI, it appears as linear or tubular intermediate tumor signal intensity expanding a vessel in the mesorectal fat.
MRI Appearance
- T2WI: Intermediate signal intensity within expanded mesorectal vessels
- Tubular or serpentine morphology following vessel course
- Contiguous with or near the primary tumor
- May extend to the Mesorectal Fascia
Prognostic Significance
EMVI is one of the most important prognostic factors in rectal cancer:
- Associated with decline in overall survival and disease-free survival
- MRF involvement by EMVI → 30.4% local recurrence rate (Birbeck et al.)
- EMVI is a high-risk feature that drives the need for nCRT or TNT
- EMVI or tumor deposits at MRI have significant prognostic impact independent of T and N stage
MRF Involvement by EMVI
- EMVI <1 mm from the MRF = MRF involvement (expert consensus)
- This triggers consideration for nCRT
- Must measure from the most extending component of the EMVI to the MRF
Relationship to Tumor Deposits
EMVI and Tumor Deposits are closely related:
- Tumor deposits may represent in-transit tumor thrombi within vessels (originally described by Gabriel, 1935)
- The “comet tail” sign at MRI: heterogeneous nodule contiguous with tumor thrombus in a vessel
- When comet tail is absent, round heterogeneous spiculated nodules may be either tumor deposits or spiculated lymph nodes (cannot be distinguished on imaging)