A fistula is an abnormal connection (tract) between 2 surfaces of the body.
This can happen anywhere in the body. It is often due to an underlying infection that spreads, affecting tissues around the original site. Depending on the location, this can lead to considerable pain and suffering.
What is an Anal Fistula?
An anal fistula thus refers to an abnormal connection between the skin (around the anus) and the internal surface of the anus (anal canal) or rectum. It is also commonly known as a fistula-in-ano.
They commonly result from infected anal glands. Conversely, 50% of the anal abscess has an underlying fistula.
A raised reddish swelling on the anal skin is common. Patients also complain of a cycle of infection with a painful swelling, intermittent discharge of pus or blood, followed by a period of calm, only to have this repeat itself in a couple of weeks or months.
During an infection, there may be perianal cellulitis (redness of the anal skin), pain, swelling, and fever. If the pain is severe, there may be a difficulty with urination.
Our specialist will obtain a medical history and perform a detailed physical examination. Most fistula can be identified by the reddish swelling on the skin around the anal opening. This represents the external opening of the fistula and gentle pressure may reveal some pus or blood flowing out from this opening. A gentle digital rectal examination may reveal the tract inside the anus, although it is often not possible to see the internal opening without more detailed tests, such as an MRI.
Surgery is the most effective treatment in most cases. The type of surgery depends on the nature of the fistula, ie. the location of the opening and the amount of anal muscles that it involves. The key to any anal fistula surgery is to find the internal opening and ensure that it is closed or removed. Our specialist will personalise your treatment, based on your medical history and type of fistula.
Surgery is usually performed under general anaesthesia, and can usually be done as a day surgery procedure, not requiring an overnight stay. It involves a precise balance of cutting enough muscle to minimise recurrence, and not cutting too much muscle to minimise incontinence.
Main treatment options for anal fistula include:
Fistulotomy or Lay Open
The most straightforward type of surgery is the lay open or fistulotomy. This involves cutting a small part of the anal sphincter muscle to open up the tract, which will then heal from the inside out.
This is only suitable for fistula that does not involve a lot of muscle, where the risk of incontinence is minimal.
A seton is a surgical thread made of plastic or rubber that is placed into the tract and secured onto the anus muscle. This technique is used when the internal opening of the fistula is in the rectum or high in the anus, which makes lay open not safe as it would cut a lot of muscle and result in incontinence. Another reason for a seton is where there is an infection or multiple fistula tracts, eg. in patients with Crohn’s disease, and this may be part of a staged procedure.
The seton allows the pus in the fistula to drain out while allowing the seton to gradually and safely cuts through the muscle while allowing it to heal, thereby moving the tract downwards toward the skin. A second operation may be needed to remove the seton once it has moved down to a safe level or when the infection has settled.
The seton technique is a very safe procedure without the risk of damaging the sphincter muscles. However, its major disadvantage is that it most often requires a second or more surgery.
Advancement Flap Procedure
This is a more complex procedure where the internal opening is cut away, then freeing up the inner lining of the anal canal nearby (the flap) and moving (advancing) it upwards to cover the previous internal opening from the inside.
This used to be the only available treatment for more complex fistulas with higher internal openings, that are not suitable for lay open.
The Ligation of Intersphincteric Fistula Tract (LIFT) procedure involves identifying the fistula tract between the internal and external sphincter muscle groups, and then tying and cutting the fistula tract there. Its purpose is for tracts that pass through muscle and this technique thereby aims to minimise muscle cutting, thereby reducing the risk of incontinence.
This makes use of a special material (called fibrin glue) to fill up the cavity of the tract. It is a simple technique where the fibrin is injected to fill up the tract, stimulating the ingrowth of the body’s own tissues to close up the tract. The sphincter muscles are not cut and hence there is minimal risk of causing damage to the muscles and incontinence.
However, the success rate of this procedure is lower than the others.