Epidemiology of rectal cancer:
Colorectal cancer is the third most prevalent cancer in men and the second most prevalent in women[1]. The incidence is higher in developed countries. Meantime, the mortality percentage in developed countries is lower, reflecting increased screening and improvements in rectal cancer diagnostic, staging, and therapy[2]. (Fig. 2).
Importance of MRI in rectal cancer:
In primary rectal cancer, MRI imaging plays a role in staging and treatment proposals[3,4,5]. (Fig 3).
Currently, surgical resection with appropriate neoadjuvant combined therapy is the mainstay in rectal cancer treatment[6].
The practice of total mesorectal excision (TME) and the selection of chemoradiotherapy (CRT) for patients with locally advanced rectal cancers (LARCs) are the usual treatment of rectal cancer. Diagnostic based on MRI features has led to significant advances in local disease control[7,8].
In the preoperative setting, MRI can assist:
- in selecting patients with LARC who are suitable for treatment with neoadjuvant CRT;
-in conducting surgeons in surgical planning;
-in recognizing the worst prognostic determinants, including EMVI, mucin content, and involvement of the mesorectal fascia (MRF)[5,9].
EMVI: What is it?
EMVI is a tumoral invasion of the venous structures exceeding the muscle layer, with the presence of a tumor inside the endothelium lined space that is either enclosed by a rim of muscle or contains red blood cells[10]. (Fig 4).
Radiological characteristics of rectal veins x EMVI:
Veins throughout the rectum are recognized on T2-weighted images as serpiginous or tortuous linear structures that seem black due to the blood signal void.
Smaller vessels can be observed penetrating the typical external rectal wall and creating a low to intermediate signal intensity in tubular structures on T2-weighted images - these are natural vessels and should not be confused with EMVI. Venous invasion into these venules can be recognized by their expansion and irregularity near to the tumor due to contiguous tumor extension[11,12]. (Fig 5).
Indicative signs for EMVI are as follow:
(a) The appearance of tumor signal intensity in a vascular structure;
(b) Expanded vessels;
(c) Tumoral expansion through and exceeding the vessel wall, interrupting the vessel border.