fistula-in-ano, is an abnormal connection between the epithelialisedsurface of the anal canal and (usually) the perianal skin.
Anal fistulae originate from the anal glands, which are located between the two layers of the anal sphincters and which drain into the anal canal. If the outlet of these glands becomes blocked, an abscess can form which can eventually point to the skin surface. The tract formed by this process is the fistula.
Abscesses can recur if the fistula seals over, allowing the accumulation of pus. It then points to the surface again, and the process repeats.
Anal fistulas per se do not generally harm, but can be very painful, and can be irritating because of the pus-drain (and, it is not unknown for formed stools to be passed through the fistula); additionally, recurrent abscesses may lead to significant short term morbidity from pain, and create a nidus for systemic spread of infection.
Surgery is considered essential in the decompression of acute abscesses; repair of the fistula itself is considered an elective procedure which many patients elect to undertake due to the discomfort and inconvenience associated with a draining tract.
Anal fistulae can present with many different symptoms:
- Discharge - either bloody or purulent
- Pruritus ani - itching
- Systemic symptoms if abscess becomes infected
Diagnosis is by examination, either in an outpatient setting or under anaesthesia(referred to as EUA - Examination Under Anaesthesia). The examination can be ananoscopy.
- The opening of the fistula onto the skin may be seen
- The area may be painful on examination
- There may be redness
- An area of induration may be felt - thickening due to chronic infection
- A discharge may be seen
- It may be possible to explore the fistula using a fistula probe (a narrow instrument) and in this way it may be possible to find both openings of the fistula
Various types of fistulas include:
- Blind: with only one open end
- Complete: with both external and internal openings
- Incomplete: a fistula with an external skin opening, which does not connect to any internal organ
Although most fistulas are in forms of a tube, some can also have multiple branches.