Fig. 5
From: MRI anatomy of the rectum: key concepts important for rectal cancer staging and treatment planning
Schematic coronal drawing a showing the different layers of the anal canal and pelvic floor. The dotted line represents the intersphincteric plane. The coronal T2-weighted MRI in b is an example of a 62 year old male patient with a cT3a tumour (white arrow showing an irregular rectal wall with ± 1 mm perirectal extension) that extends into the anal canal and invades the right internal anal sphincter. The coronal image in c is an example of a 59-year-old female patient with a cT4b rectal tumour that invades the internal sphincter on both sides and extends into the external sphincter, levator ani, and puborectalis muscles on the left side