**2.3 Pathways of spreading**

*Colorectal Cancer*

T1- submucosal invasion.

of T3 has been created:

**Figure 4.**

poor prognosis [1].

T2- invasion of muscularis propria.

*Mucosal layers of rectal wall (axial T2 weigted MR image).*

T3- through the muscularis propria to the submucosa.

T3a - minimal invasion <1 mm by muscularis propria. T3b- light-walled invasion 1-5 mm from muscularis propria. T3c- moderate invasion 5-15 mm from muscularis propria. T3d- extensive invasion>15 mm by muscularis propria.

study Mercury II: Low Rectal Cancer study [2].

ness (preserved outer muscle layer).

T4- perforation of the visceral peritoneum or direct invasion of the peritoneum. Important fact is that T3 and T4 tumors are associated with extramural invasion. The more pronounced penetration of the mesorectum is associated with a worse prognosis and a higher probability of local recurrence. Many tumors are staged as pT3, but there is actually a heterogeneous T3 group, which is why a subclassification

T3a and T3b are associated with better outcome for the patient compared with T3c and T3d stages, suggested they are T4 tumors because of worse outcome and

When talking about staging it is important to notice that low rectal cancer is a separate subgroup again due to different anatomical features- the anorectal sling: Staging of low rectal cancer with MRI (recently validated in the prospective

stage 1 - the tumor is visualized in the rectal wall, but not throughout its thick-

stage 2- the tumor displaces the muscle layer without crossing the intersphinc-

**60**

teric line.

For understanding of the neoplastic behavior of rectal cancer it is of great importance to analyze the pathways of spreading of tumorous tissue. They are:

1.direct invasion in the rectal wall,

2.involvement of local lymph vessels and lymph node metastases,

3.venous invasion (intra- and extramural venous invasion- EMVI) and

4.tumor deposits.

Demonstration of any invasion both histologically and by MRI [3] is always associated with a poor prognosis. The detection of EMVI is associated with the presence of synchronous distant metastases. Involvement of extramural venous vessels is more closely associated with poor prognosis, as well as invasion of larger veins. This leads to the conclusion, that detection of EMVI on MRI is of great prognostic importance and it is explained in details below.
