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An abscess is a collection of pus (due to an infection). A perianal abscess is an abscess that lies under the skin near the anus. This abscess can be right next to the anal verge 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. Certain conditions such as inflammation of the colon may make it more likely to develop a perianal abscess.
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A perianal abscess if left untreated can burst open through the skin. Oftentimes, a tunnel persists after the abscess has burst. The tunnel forms an abnormal connection between the anus and the skin and that is called an anal fistula or fistula-in-ano(FIA). This tunnel can get infected repeatedly. Once formed, the FIA rarely heals spontaneously.
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An abscess usually presents as a painful swelling near the anus. It feels warm and tender to touch. This may be associated with fever. The swelling is not related to bowel movement. 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. In between the episodes of discharge, one can develop symptoms of skin irritation such as itching or soreness around the anal fistula.
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A perianal abscess is best treated by surgical drainage. This involves making a small cut in the skin overlying the abscess and cleaning the cavity. The skin wound is left open to heal on its own and not closed with sutures. This is to avoid recurrence of the abscess. The surgery should be done under anaesthesia to allow the surgeon to identify possible anal fistula tracts accurately.
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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 options at surgery currently available are:
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- Fistulotomy (cutting open the fistula tract)
- Fistulectomy (complete removal of the fistula tract and closing the wound)
- Loose (drainage) seton (inserting a string/rubber band to prevent re-infection)
- Tight (cutting) seton (inserting a string that cuts through the anal muscles gradually)
- Anal fistula plug (plugging the fistula tract with a composite material which dissolves in time)
- Rectal mucosal advancement flap (pulling the inner lining from above to close the inner opening)
- Ligation of Inter-sphincter Fistula Tract (LIFT) procedure (surgery for complex FIA)
- Video-Assisted Anal Fistula Treatment (VAAFT) (advanced technique for complex FIA)
- Defunctioning colostomy (diverting stools to prevent infection)
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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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Simple FIA and perianal abscesses can usually be treated as day-case operations and patients are discharged home on the same day. Complex FIA cases may require hospitalization of 1-2 days depending on the complexity of the case. Painkillers and antibiotics will be prescribed after surgery.
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There will be an open wound near the anus, the size depending on complexity of surgery. Small wounds can be cleaned easily by washing with tap water. Larger wounds may require daily dressing change in the clinic to aid good healing. Most wounds of simple anal fistula will heal spontaneously after 2-3 weeks. Complex fistula wounds may take up to 6 weeks to heal completely.
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You will have to avoid strenuous physical activity especially swimming until the wound heals. You may need to stay home from work for the first 2-3 weeks as that is the most uncomfortable period.
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An anal fistula (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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