Fig. 2
From: MRI of rectal cancer—relevant anatomy and staging key points
The upper limit of the rectum corresponds on MR imaging to the point of inflexion between the more vertical rectum and the more horizontal sigmoid “take off” (arrow in a). The sigmoid starts at another more horizontal inflection, better visualised in the (oblique) axial plane (arrow in b). The low rectum is the segment located < 6 cm above the anal verge and above the anorectal transition (lined in yellow in a); the mid-rectum is located between the low rectum and the plane of the lowest point of the anterior peritoneal reflection (lined in purple in a); the high rectum is the segment above it and below the sigmoid “take-off” (lined in pink in a). The sigmoid “take-off” or rectosigmoid transition is lined in blue in b, while the actual sigmoid is lined in green