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The conditions of fistula and abscess of the anal area are intimately related. Infection within the anal glands (that lie between the two layers of the anal sphincter muscle) may occur for reasons that are unclear and result in one of two conditions. Where the infection is acute an abscess may develop, this may drain spontaneously or require surgical treatment.
Should an infection becomes chronic a fistula (abnormal communication between bowel lining and skin) may develop which virtually always requires surgical correction. On rare occasions abscesses and fistulas may be caused by other conditions of the anus and rectum such as Crohn’s disease and cancer. Fistulas may be simple or, much less commonly complex, involving a variety of other sites within the abdomen and pelvis as well as the anal canal.
Abscesses and fistulas may be investigated in clinic by physical examination, by examination under general anaesthesia (EUA) or by MRI scanning.
What are the symptoms?
- Anal pain (especially on defaecation)
- Swelling around the anus
- Discharge (of blood or pus)
- Anal discharge (of blood or pus)
- Itching and pain
- Recurrent abscesses
Usually requires drainage with surgery under general anaesthesia although small abscesses may be managed with antibiotics or discharge spontaneously. Resulting wounds may take considerable time to heal and while they do discharge and require frequent dressing changes. Most heal completely.
About 40% of perianal abscesses treated by whatever means above will develop a fistula, a track between the lining of the anal canal and the skin of the area around the anus. These require treatment by means of a laying open procedure (where the track is split open from inside to out and left exposed to heal from below), a drainage seton inserted (a rubber band is placed via the skin into the fistula, out through the anal canal and tied outside) or a fistula plug placed within the track.
Treatment is usually straightforward but may be complicated and protracted requiring more than one operation over months or in rare cases years. The choice of operation requires the attention of a specialist surgeon who will often make the final decision about the procedure performed whilst the patient is under general anaesthetic. A laying open procedure involves division of a variable portion of the sphincter muscle. For the most part this is safe and causes no longer term continence issues but if a significant portion of the sphincter is involved particularly in women (especially those who have had children) and the elderly, every attempt is made to leave the muscle intact.
A seton is secured loosely within the fistula track and remains in situ for several months. Most patients tolerate their presence without dificulty. Sustained traction on the seton, particularly when walking, results in the seton slowly working its way to the skin surface with the muscle beyond it healing as it goes. A further operation may be required at a later date to finally remove the seton or it may fall out having done its job.