Anorectal abscesses, and Fistula-in-ano

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What is Anorectal abscesses, and Fistula-in-ano?

Anorectal abscess, and Fistula-in-ano occur in the Rectum and anus.

An abscess is a localised collection of pus. In this case it can either occur near the anus close under the skin, or deeper, adjacent to the rectum.

A "fistula" is an abnormal communication/track between two epithelial surfaces - in the case of fistula-in-ano, between the ano-rectal passage and the surface skin near the anus. It occurs as a complication of an ano-rectal abscess which has discharged to the skin, with the track from anorectal passage to the skin remaining patent.

Who gets Anorectal abscesses, and Fistula-in-ano?

Perianal abscesses are common conditions. Their exact incidence is unknown. A fistula-in-ano complicates 30-50% of perianal abscesses.
They are more common in patients with Inflammatory Bowel Disease (in particular Crohn's disease) and Diabetes Mellitus.

Predisposing Factors

Perianal abscesses occur as a result of a blocked anal gland that subsequently becomes infected - and thus an abscess forms. They are more common in patients with Diabetes Mellitus, Crohn's disease, and patients who are immunocompromised for any reason.

Fistula-in-ano frequently complicates the above conditions, but it can also be idiopathic (of unknown cause), or arise in patients with tuberculosis, trauma (especially obstetric - after traumatic delivery), carcinoma, pelvic inflammatory disease, radiation damage (post radiotherapy).

Progression

Anorectal abscess if left alone will discharge to the skin, but then the complication of fistula-in-ano will often (30-50%) occur, which will not heal spontaneously. Surgical treatment is, however, usually successful. Neglected fistulas can result in repeated abscesses, multiple openings and complications.

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