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A perianal abscess is a collection of pus (due to an infection) that lies under the skin near the anus. This abscess can be right next to the anus or as far as several centimeters away in one of the buttocks. A perianal abscess usually starts from bacterial infection of an anal gland which is situated inside the anal canal. A perianal abscess if left untreated can burst open through the skin leaving a tunnel. The tunnel forms an abnormal connection between the anus and the skin and that is called an anal fistula or fistula-in-ano (FIA). Once formed, an FIA requires surgery.
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An abscess usually presents as a painful swelling near the anus. It feels warm and tender to touch. If the abscess bursts, there can be a purulent (yellow) or bloody discharge. The discharge is usually accompanied by partial relief from the pain of swelling. Repeated discharge from a lump near the anus usually marks the outer opening of the anal fistula.
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A perianal abscess is best treated by surgical drainage. The surgery should be done under anaesthesia to allow the surgeon to identify possible anal fistula tracts accurately. Treatment of anal fistula (FIA) is slightly more complicated. Once again, surgery is required. A large majority of cases are classified as simple FIA. Occasionally, the fistula tract runs across a large amount of anal sphincter muscle or has multiple complicated tracts. That is called a complex FIA. The options available for surgery are varied and merely summarized here. For more details, the discussion is best done in the clinic.
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The treatment options are:
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The diagnosis of a simple anal fistula (FIA) is made on clinical assessment alone. No further tests are required before surgery. For complex FIA, an endoanal ultrasound provides accurate mapping of the fistula tract(s). An alternative to endoanal ultrasound is MRI of the anus. Accurate mapping of the fistula tract architecture is essential for proper planning and selection of surgical options.
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An FIA if left untreated will lead to repeated infections. Each episode of infection can be different and can be severe. It is better to have treatment of a small simple FIA than a large abscess from a complex FIA. Furthermore, there is good evidence that if an anal fistula is left untreated for several years, there is a risk that the anal fistula can become a cancer.
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