Anal fistulas are usually the result of an infection near the anus causing a collection of pus (abscess) in the nearby tissue. When the pus drains away, it can leave a small channel behind.

An anal abscess is a fluid-filled cavity usually caused by an infection of the anal glands. These glands can become infected if they are clogged with faecal matter or any type of foreign substance. Some people with anal abscesses – approximately 50 percent – will also develop an anal fistula, which is characterized by a tunnel within the skin connecting the clogged glands to the abscess.

Frequently Asked Questions

What are the symptoms of an anal abscess or fistula?

The most common symptom of an abscess or fistula is constant, throbbing pain that worsens when sitting down. An abscess may lead to pain during bowel movements, which can also lead to secondary constipation. Anal abscesses typically cause visible boil-like swelling and irritation to the skin around the anus. Some abscesses are warm to the touch and cause fever.

What are the causes of an abscess?

The vast majority of abscesses are caused by blockages and infections within the anal glands. However, other conditions may also lead to abscess, such as an infected anal fissure or certain sexually transmitted infections. Anyone can develop abscess, though certain GI health conditions, such as inflammatory bowel disease or AIDS, can increase a person’s risk.

How can a colorectal surgeon treat an abscess?

The standard treatment for abscesses is surgical drainage of the pus inside of them. This procedure is quick and usually successful. If a fistula is present at the time of drainage, a surgeon may choose to address it at the same time through one of several treatment options. Many people do not develop fistulas until several weeks or even years after an abscess has been drained.

How is a fistula treated?

A fistula nearly always requires surgery to cure it.

The majority of fistulae are relatively easy to treat but should preferably be performed by a specialist in colorectal (bowel) surgery.

The surgery usually involves the fistula track being laid open surgically. This may involve cutting a small part of the anal sphincter muscle away. In this way, the tunnel is opened up (‘deroofed’) to form a trench or groove that heals from the bottom of the trench outwards.

In the same way as for the healing of an abscess cavity, it will usually take a few weeks for the fistula that has been removed to fill up with scar tissue. Once again, the surgery usually requires a general anaesthetic and can be done as a day-case procedure.

It may be necessary for a gauze pad to be worn in the underwear for a week or two after the operation to prevent the drainage from soiling the clothes.

Bowel movements will not affect the healing.

Sometimes the fistula is not the type that can be simply laid open as too much anal sphincter muscle is involved to be cut (which may risk incontinence) or there are multiple tracks. In this case a string may be passed through the track (“seton”) and the surgeon will bring you back and discuss further options for your treatment.

What if the problem comes back?

Fistulae can be particularly awkward conditions to treat and can come back. In this case – and for the more complicated fistulae, it may be necessary to do a MRI (magnetic resonance scan) scan of the back passage to check that no other fistulae or “tracks” have been overlooked.

If the fistula is a complicated one, a number of alternative operative approaches are available. Your surgeon will discuss these with you if they are necessary.

How long does it take to recover from this type of surgery?

Discomfort after fistula surgery is moderate for the first week and can be controlled with simple pain killers. The amount of time off work is usually minimal but will depend on the type of job you do.

Bathing or showering two to three times a day helps keep the area clean and comfortable. Laxatives are recommended to minimise the discomfort associated with passing a motion.