MRI has shown high specificity and moderate sensitivity and could be a good option to detect extramural venous invasion among colorectal cancer patients, especially with high-resolution MRI technology.
Extramural venous invasion (EMVI) (i.e., cancer spreading through the blood vessels) is a significant marker in predicting the outcomes for colorectal cancer—as the presence of EMVI has been shown to increase the odds that a patient’s cancer will come back, spread to distant parts of the body, and lead to death.
Such insights can be tremendously helpful for oncologists, surgeons, and other providers as they assess whether their patients have EMVI, and thus, stand to gain the most from interventions in light of the risks. This is especially true considering that the current treatment guidelines for colorectal cancer (chemoradiation therapy and/or surgery) come with the possibility of adverse effects, such as bowel or sexual impairment.
But how can physicians detect EMVI? A common option is with surgicopathologic confirmation, or surgically extracting a sample and examining it in vitro. However, that procedure, as with other interventions, comes with risks that may only be worth taking among certain populations of patients.
So the question may not just be, How can we detect EMVI?, but rather: How can we detect EMVI non-invasively? For that, providers may want to turn to magnetic resonance imaging (MRI)—the imaging tool otherwise used in staging workups for rectal cancer (and, increasingly, colorectal cancer as well, in lieu of CT).1
MRI and EMVI: What the Research Says
MRI has shown high specificity and moderate sensitivity and could be a good option to detect EMVI among colorectal cancer patients, especially with more powerful advancements of the technology by way of high-resolution MRI.
At least, that was the takeaway from a recent meta-analysis of scientific literature published in the American Journal of Roentgenology, in which authors reviewed 14 moderate-quality articles examining the utility of MRI in detecting EMVI among a total of 1,751 colorectal cancer patients.
In their results, the authors of the meta-analysis found that MRIs yielded a collective sensitivity and specificity of .61 and .87, respectively. In studies that engaged high-resolution MRI, the specificity was even higher compared to those without high-resolution MRI (.89 vs. .78)—thanks to the ability of high-resolution equipment to detect microscopic vascular changes that regular technology cannot. Authors defined high-resolution MRI as equipment with T2-weighting, as well as in-plane voxel scale that was less than .8 mm.
And while they only found moderate sensitivity values, the authors noted that the high specificity findings indicate that MRI may still have the potential to offer preoperative utility among colorectal cancer patients—and even more so if future research findings validate the results.1
After all, patients with MRI-detected EMVI (mrEMVI) experience higher rates of synchronous and postoperative metastases—by as much as five and four times, respectively.2 mrEMVI assessment has also revealed telling insights related to survival: In one study among 478 rectal cancer patients, the three-year disease-free survival rates of patients with stage II with EMVI nearly matched that of stage III of the disease.1 Those insights align with previous research, which has found that EMVI-positive pre-treatment MRIs resulted in rectal cancer survival rates that were less than half of EMVI-negative MRIs (35 percent vs. 74 percent).3
Finding EMVI: Imaging Guidelines and What to Look For
Given the successes of pre-treatment MRI at detecting EMVI, you might think its use would be more ubiquitous among cancer care providers—but the numbers paint a different story. For example, only about 1 in 2 treating physicians assess EMVI with preoperative MRI, 1 despite the fact that the majority of them acknowledge the importance of considering EMVI for treatment planning.4
For physicians who do rely on MRI to detect EMVI, it’s worth understanding the radiographic features that indicate changes in the vascular network. According to Radiopaedia, those changes manifest as cylindrical or serpiginous abnormalities, characterized with intermediate or hypointense signals, and which travel along the path of the perirectal vein, either attached or detached from the tumor.
The extent of vascular invasion is typically measured by the mrEMVI score, a scale from 0 to 4 in which 0-2 represents no presence of EMVI and 3-4 indicates EMVI presence.3
Clinical Applications of mrEMVI
All told, the meta-analysis indicates that MRI indeed has prognostic value for assessing colorectal cancer patients—but the authors add that further research is needed to validate the findings of prior conclusions.
Specifically, clinicians should be aware of this paper’s limitations, namely the substantial heterogeneity (i.e., a wide range of disparity between findings) among the research analyzed as part of the collective pool—which further warrants additional investigation before applying these conclusions to the clinic. The authors noted three factors that led to those disparities, including high T category, antispasmodic agents, and high-resolution MRI.1
Other researchers have also encouraged caution before explicitly applying similar findings to treatment decisions, although some researchers have recommended assessing mrEMVI status in certain circumstances—such as with rectal tumors with mesorectal fascia or invasion depth that exceeds 5 mm.5
Growing Our Understanding of a Deadly Disease
More generally, the focus of the paper evaluates a topic at depth which continually gets attention among colorectal cancer providers—that of using MRI to noninvasively detect EMVI and predict patient outcomes. Recently in Radiology, Zhang et. al. contributed to the discussion by portraying mrEMVI as a potential “new marker for patient prognosis.”6
As more research adds clarity to the diagnostic utility of mrEMVI, it could potentially help physicians better tailor treatment decisions to the unique needs of patients. Those decisions rely on a thorough assessment of the risks of interventions, such as surgery or chemoradiation, versus the potential benefits they yield. 1
For a cancer that claims the lives of about 1.8 million people globally each year,7 such insights are certainly welcome ones as we grow our understanding of colorectal cancer pathology, imaging, and treatment—as well as work to improve the patient experience overall.
1. The Diagnostic Performance of MRI for Detection of Extramural Venous Invasion in Colorectal Cancer: A Systematic Review and Meta-Analysis of the Literature, American Journal of Roentgenology, https://www.ajronline.org/doi/full/10.2214/AJR.19.21112. Accessed Oct. 14, 2019.
2. A meta-analysis comparing the risk of metastases in patients with rectal cancer and MRI-detected extramural vascular invasion (mrEMVI) vs mrEMVI-negative cases, British Journal of Cancer, https://www.ncbi.nlm.nih.gov/pubmed/28449006?dopt=Abstract. Accessed Oct. 14, 2019.
3. Extramural Vascular Invasion, Radiopaedia, https://radiopaedia.org/articles/extramural-vascular-invasion-emvi-1?lang=us. Accessed Oct. 14, 2019.
4. Adjuvant therapy decisions based on magnetic resonance imaging of extramural venous invasion and other prognostic factors in colorectal cancer, Annals of the Royal College Surgeons of England. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4473443/. Accessed Oct. 14, 2019.
5. Predictive value of MRI-detected extramural vascular invasion in stage T3 rectal cancer patients before neoadjuvant chemoradiation, Diagnostic and Interventional Radiology, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5951200/. Accessed Oct. 14, 2019.
6. MRI of Extramural Venous Invasion in Rectal Cancer: A New Marker for Patient Prognosis?, Radiology, https://pubs.rsna.org/doi/abs/10.1148/radiol.2018181689?journalCode=radiology. Accessed Oct. 14, 2019.
7. Cancer, World Health Organization, https://www.who.int/news-room/fact-sheets/detail/cancer. Accessed Oct. 14, 2019.