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    Anal Abscess and Fistula

    Where to Seek Treatment
    Singapore General Hospital
    Contributed by Centre for Digestive and Liver Diseases (CDLD)
    Patient assessment for colorectal disease at SGH.


    An anal abscess is an infected cavity filled with pus found near the anus or rectum. An anal fistula is a small tunnel connecting the anal gland from which an abscess arose to the skin of the buttocks outside the anus.


    Multiple factors can result in a person developing symptomatic piles and these are generally associated with any condition that can cause an increase in the intra-abdominal pressure.

    • Persistent straining during bowel movement and sitting on the toilet for a long period of time.
    • Chronic constipation and diarrhoea.
    • Pregnancy.
    • Low fibre diet.
    • Obesity.
    • Intra-abdominal or pelvic tumour.

    An anal abscess usually results from an acute infection of a small gland just inside the anus, when bacteria or foreign matter enters the tissue through the gland. Certain conditions, for example, inflammation of the intestine or colitis, can sometimes make these infections more likely.

    After an abscess has been drained, a tunnel may persist connecting the anus or rectum to the skin. This is known as anal fistula. Persistent drainage of pus from the outside opening may indicate the presence of this tunnel.


    Symptoms of both ailments include fever, constant pain, redness and swelling around the anal area. Other symptoms include discharge of pus (which often relieves the pain) and fever.


    Anal abscess and fistula are usually diagnosed via bedside examination of the anus and perianal area. Occasionally, further imaging investigations such as endoanal ultrasound or magnetic resonance imaging are required for surgical planning in complex cases.

    Colonoscopy is sometimes performed to exclude other conditions.


    Anal abscesses are usually treated with an operation to make an opening over the abscess to allow drainage of the pus. This can be done as a day surgery except in cases where they are big or deep in which they will need to be hospitalised for a few days for dressing.

    Surgery is the mainstay of treatment for anal fistulas. Fistula surgery usually involves cutting a small portion of the anal sphincter muscle to open the tunnel and convert the tunnel into a groove that will then heal from within outward.

    Occasionally, a suture is left is left in the fistula first followed by a second operation to cut the fistula at a later period.

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