ABSTRACT
The ‘anus’ is a general term for the outlet of the bowel and includes both the anal canal and peri-anal skin. The anal canal is defined in the major international cancer staging systems as that part of the intestine that extends from the rectum to the junction with the hair-bearing skin of the peri-anal region.1,2 The canal is 3-4 cm long, the superior limit being the palpable upper border of the anal sphincters and puborectalis muscles of the anorectal ring, and the distal limit, or anal verge, the level at which the walls of the canal come into contact in their normal resting state.3 The peri-anal area is the skin within a 5 cm radius of the anal verge. The term anal margin is used, often ambiguously, as a synonym for the distal canal and anal verge, the peri-anal skin immediately adjacent to the distal limit of the anal canal, or the peri-anal area as a whole.
