Tumours and Tumour‐Like Conditions of the Anorectal Region

The anal canal has a complex anatomy and histology. Multiple different types of mucosa are present within the anal canal, knowledge of which is crucial to understanding tumorigenesis at this site. Within the anal canal, at the dentate line, columnar/colonic type mucosa abuts squamous mucosa, with areas of intervening transitional-type mucosa. At this level anal glands also drain into the anal canal. The lower aspect of the anal canal lies in direct continuity with perianal skin, so not only may the anal canal develop those tumours commonly seen involving either the colorectum or perianal skin, but also a number of additional tumour types may develop that arise from anal squamous or transitional-type mucosa and anal glands.