Fig. 3
From: MRI of rectal cancer—relevant anatomy and staging key points
The rectal wall. The mucosa is visible on T2-weighted imaging as a regular thin (≈ 1 mm) hypointense line delimiting the lumen (red arrow in a). The submucosa is hyperintense and of variable thickness (double-headed blue arrow in a). It may not be visible when the rectum is distended. The muscularis propria is composed of an inner circular layer (green arrow in a) and an outer longitudinal layer (purple arrow in a) which may be separated by a thin layer of fat, as in the example shown. Lying externally to it is a cushion of mesorectal fat (delimited in red in a) that tappers inferiorly (delimited in red in c) and anteriorly, where it can be thin (between arrows in c) or even invisible (between arrows in d), in which case the mid/low rectum appears juxtaposed to the Dennonvillier fascia