What is Anorectal Abscess 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.

Anorectal abscess and fistula-in-ano image

Statistics on Anorectal Abscess 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.

Risk Factors for Anorectal Abscess and Fistula-in-Ano

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 of Anorectal Abscess and Fistula-in-Ano

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.

Symptoms of Anorectal Abscess and Fistula-in-Ano

Pain and swelling in the anal region with wetness and soiling, often on a background of Crohn’s disease. In the acute setting, the abscess causes pain and swelling which occurs when sitting and is aggravated by motion, coughing and straining. Fever, diarrhoea, purulent discharge and bleeding may also occur. The pain is throbbing, continuous and worsened by bowel motions. The discharge on the skin causes erosion, excoriation and pruritis.

Chronic fistula may present with discharge on the buttocks and pruritis, and the pain is usually less prominent.

How is Anorectal Abscess and Fistula-in-Ano Diagnosed?

No general investigations are required for the diagnosis of the above conditions. A full blood count and blood sugar level can be used to screen for an inflammatory disorder or diabetes.

Prognosis of Anorectal Abscess and Fistula-in-Ano

Surgical treatment is usually successful in treating anorectal abscesses or fistula-in-ano. Abscesses that are deeper, involving the upper portion of the anal sphincters (further away from the anus) are more complex and require specialist treatment to avoid the complication of faecal incontinence if the internal sphincter is damaged.

How is Anorectal Abscess and Fistula-in-Ano Treated?

Treatment of an anorectal abscess is by surgery – it can be drained under local anaesthesia, or sometimes general anaesthesia for bigger, deeper abscesses. There is little role for antibiotics unless the patient is systemically unwell.

Surgical correction is the treatment of choice for a fistula-in-ano because spontaneous healing of a fistula is rare. A fistulotomy is used to open the track and subsequently allow it to heal. Fistulas in Crohn’s disease may be more difficult to treat.

Anorectal Abscess and Fistula-in-Ano References

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  9. Fistula [online]. Bethesda, MD: Medline Plus; 2003 [cited 31 October 2003]. Available from: URL link