Overview

An anal fistula is a small tunnel that develops between the end of the bowel and the skin near the opening of the bottom (anus).

It's usually caused by an infection near the anus, which results in a collection of pus (abscess) in the nearby tissue.

When the pus drains away, it can leave a small channel behind.

Anal fistulas can cause unpleasant symptoms, such as discomfort and skin irritation, and will not usually get better on their own.

Surgery is recommended in most cases.

Symptoms of an anal fistula

Symptoms of an anal fistula can include:

• skin irritation around the anus
• a constant, throbbing pain that may be worse when you sit down, move around, poo or cough
• smelly discharge from near your anus
• passing pus or blood when you poo
• swelling and redness around your anus and a high temperature if you also have an abscess
• difficulty controlling bowel movements (bowel incontinence) in some cases

The end of the fistula might be visible as a hole in the skin near your anus, although this may be difficult for you to see yourself.

When to get medical advice

See a GP if you have persistent symptoms of an anal fistula. They'll ask about your symptoms and whether you have any bowel conditions.

They may also ask to examine your anus and gently insert a finger inside it (rectal examination) to check for signs of a fistula.

If the GP thinks you might have a fistula, they can refer you to a specialist called a colorectal surgeon for further tests to confirm the diagnosis and determine the most suitable treatment.

Tests you may have include:

• a further physical and rectal examination
• a proctoscopy – where a special telescope with a light on the end is used to look inside your anus
• an ultrasound scan, MRI scan or CT scan

Causes of anal fistulas

Most anal fistulas develop after an anal abscess. They can occur if the abscess does not heal properly after the pus has drained away.

Less common causes of anal fistulas include:

• Crohn's disease – a long-term condition in which the digestive system becomes inflamed
• diverticulitis – infection of the small pouches that can stick out of the side of the large intestine (colon)
• hidradenitis suppurativa – a long-term skin condition that causes abscesses and scarring
• infection with tuberculosis (TB) or HIV
• a complication of surgery near the anus

Treatments for an anal fistula

Anal fistulas usually require surgery as they rarely heal if left untreated.

The main options include:

• a fistulotomy – a procedure that involves cutting open the whole length of the fistula so it heals into a flat scar
• seton procedures – where a piece of surgical thread called a seton is placed in the fistula and left there for several weeks to help it heal before a further procedure is carried out to treat it

All these procedures have different benefits and risks. You can discuss this with the surgeon.

Many people do not need to stay in hospital overnight after surgery, although some may need to stay in hospital for a few days.

Treatment

Surgery is often needed to treat anal fistulas as they do not usually heal by themselves.

There are several different procedures.The best option for you will depend on the position of your fistula and whether it's a single channel or branches off in different directions.

Sometimes you may need to have an initial examination of the area under general anaesthetic (where you're asleep) to help determine the best treatment.

The surgeon will talk to you about the options available and which one they feel is the most suitable for you.

Surgery for an anal fistula is usually carried out under general anaesthetic. In many cases, it's not necessary to stay in hospital overnight afterwards.

The aim of surgery is to heal the fistula and avoid damaging to the sphincter muscles (the ring of muscles that open and close the anus). Damaging the sphincter muscle could potentially result in loss of bowel control (bowel incontinence).

The main surgical options are outlined here.

Fistulotomy

The most common type of surgery for anal fistulas is a fistulotomy. This involves cutting along the whole length of the fistula to open it up so it heals as a flat scar.

A fistulotomy is the most effective treatment for many anal fistulas. But it's usually only suitable for fistulas that do not pass through much of the sphincter muscles. This is because the risk of incontinence is lowest in these cases.

If the surgeon has to cut a small portion of anal sphincter muscle during the procedure, they'll make every attempt to reduce the risk of incontinence.

In cases where the risk of incontinence is considered too high, another procedure may be recommended instead.

Seton techniques

If your fistula passes through a significant portion of anal sphincter muscle, your surgeon may initially recommend inserting a seton.

A seton is a piece of surgical thread that's left in the fistula for several weeks to keep it open.

This allows it to drain and helps it heal, while avoiding the need to cut the sphincter muscles.

Loose setons allow fistulas to drain, but do not cure them. To cure a fistula, tighter setons may be used to cut through the fistula slowly.

This may require several procedures that the surgeon can discuss with you.

Or they may suggest carrying out several fistulotomy procedures, carefully opening up a small section of the fistula each time, or a different treatment

Advancement flap procedure

An advancement flap procedure may be considered if your fistula passes through the anal sphincter muscles and having a fistulotomy carries a high risk of causing incontinence.

This involves cutting or scraping out the fistula and covering the hole where it entered the bowel with a flap of tissue taken from inside the rectum, which is the final part of the bowel.

This has a lower success rate than a fistulotomy, but avoids the need to cut the anal sphincter muscles.

LIFT procedure

The ligation of the intersphincteric fistula tract (LIFT) procedure is a treatment for fistulas that pass through the anal sphincter muscles, where a fistulotomy would be too risky.

During the treatment, a cut is made in the skin above the fistula and the sphincter muscles are moved apart. The fistula is then sealed at both ends and cut open so it lies flat.

This procedure has had some promising results so far, but it's only been around for a few years, so more research is needed to determine how well it works in the short and long term.

Endoscopic ablation

Endoscopic ablation is where an endoscope (a long, thin tube with a small camera on the end) is put in the fistula.

An electrode is then passed through the endoscope and used to seal the fistula.

Endoscopic ablation works well and there are no serious concerns about it's safety.

Laser surgery

Radially emitting laser fibre treatment involves using a small laser beam to seal the fistula.

There are uncertainties around how well it works, but there are no major safety concerns.

Fibrin glue

Treatment with fibrin glue is currently the only non-surgical option for anal fistulas.

It involves the surgeon injecting glue into the fistula while you're under a general anaesthetic. The glue helps seal the fistula and encourages it to heal.

It's generally less effective than fistulotomy for simple fistulas and the results may not be long-lasting. But it may be a useful option for fistulas that pass through the anal sphincter muscles because they do not need to be cut.

Bioprosthetic plug

Another option is the insertion of a bioprosthetic plug.

This is a cone-shaped plug made from animal tissue that's used to block the internal opening of the fistula.

This procedure works well for blocking an anal fistula and there are no serious concerns about its safety.

Risks of anal fistula surgery

Like any type of treatment, treatment for anal fistulas carries a number of risks.

The main risks are:

• infection – this may require a course of antibiotics and severe cases may need to be treated in hospital
• recurrence of the fistula – the fistula can sometimes reoccur despite surgery
• bowel incontinence – this is a potential risk with most types of anal fistula treatment, although severe incontinence is rare and every effort will be made to prevent it

The level of risk will depend on things like where your fistula is located and the specific procedure you have.

Speak to the surgeon about the potential risks of the procedure they recommend.