Aetiology

Commonly a perianal abscess is formed as result of infection arising in a perianal gland. There are 10 to 15 of these glands lying between the internal and external anal sphincters. They drain into tiny pits at the bases of the anal columns along the dentate line. The ducts through which the glands drain are very tiny and these may become obstructed by faeces and so initiate infection. The abscess that results lies between the anal sphincters and tends to point towards the skin at the anal margin. Lateral spread may occur into the ischiorectal fossa, or rarely, superiorly above the levator ani into the pararectal fossa.

There are a variety of conditions that predispose to perianal abscesses including tuberculosis, actinomycosis, mucinous carcinoma, and inflammatory bowel disease, especially Crohn's disease.