*2.1.1 Mesorectum and mesorectal fascia MRF*

It is a hypointense line that surrounds the mesorectum. Above this layer it connects with the mesorectal fascia, which lies above the levator muscles and, respectively, connects with the peritoneal reflection forward and with the parietal fascia backward (**Figure 2**).

### *2.1.2 Anorectal sling (m. levator ani) and anal verge*

Anatomically, the anal canal is at the level at which the anorectal sling envelops the rectum and creates the anorectal transition (**Figure 3**).

**59**

**Figure 3.**

**Figure 2.**

*2.1.3 Anterior peritoneal reflection*

*Anorectal complex (coronal T2 weighted MR image).*

in the proximal part of rectum.

**2.2 Mucosal layers of rectal wall**

relation to the TNM classification of the rectal cancer.

It is a thickened parietal fascia that covers the terminal veins and adipose tissue

Another anatomical landmark is differentiating the mucosal layers (**Figure 4**) in

*Role of Magnetic Resonance Imaging in Patients with Rectal Cancer*

*Mesorectum and mesorectal fascia MRF (axial T2 weighted MR image).*

*DOI: http://dx.doi.org/10.5772/intechopen.94868*

*Role of Magnetic Resonance Imaging in Patients with Rectal Cancer DOI: http://dx.doi.org/10.5772/intechopen.94868*

*Colorectal Cancer*

rectum (**Figure 1**).

backward (**Figure 2**).

**2.1 Anatomic definition of rectum**

ani) and anal verge, shown on the pictures below.

*2.1.1 Mesorectum and mesorectal fascia MRF*

*2.1.2 Anorectal sling (m. levator ani) and anal verge*

the rectum and creates the anorectal transition (**Figure 3**).

*Anatomical presence of sigmoid take-off (sagittal T2 weighted MR image).*

Knowing the anatomy, especially the anatomy on MR studies is the key to the right treatment of rectal cancer. Important anatomical landmarks are sigmoid takeoff (transition rectum-sigma), mesorectal fascia MRF and mesorectum, presacral fascia, anterior peritoneal reflection, retrorectal space, anorectal sling (m. levator

The rectum is the most distal part of the gastrointestinal tract, located before the anal canal. There are different definitions of the distal and proximal borders of the rectum – distal border is linea dentata ani, and proximal part is the sigmoid colon and the transitional part called sigmoid take-off. It is a radiological reference point used to identify the connection of the sigmoid mesocolon with the mesorectum and therefore the connection of the sigmoid colon with the

It is a hypointense line that surrounds the mesorectum. Above this layer it connects with the mesorectal fascia, which lies above the levator muscles and, respectively, connects with the peritoneal reflection forward and with the parietal fascia

Anatomically, the anal canal is at the level at which the anorectal sling envelops

**58**

**Figure 1.**

**Figure 2.** *Mesorectum and mesorectal fascia MRF (axial T2 weighted MR image).*

### **Figure 3.** *Anorectal complex (coronal T2 weighted MR image).*
