An anal fistula is a small tunnel that develops between the end of the bowel and the skin near the anus (where poo leaves the body).
They’re 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.
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 (fever) 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 surgeon 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 surgeon thinks you might have a fistula, they can do further tests to confirm the diagnosis and determine the most suitable treatment.
These may include:
- A further physical and rectal examination
- A spectroscopy, 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. You can get one 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 inflameddiverticulitis – 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
Surgery is usually necessary to treat an anal fistula as they usually do not 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 anesthetic (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 anesthetic. In many cases, it’s not necessary to stay in hospital overnight afterwards.
The aim of surgery is to heal the fistula while avoiding damage to the sphincter muscles, the ring of muscles that open and close the anus, which could potentially result in loss of bowel control (bowel incontinence).
The main 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, although it’s usually only suitable for fistulas that do not pass through much of the sphincter muscles, as the risk of incontinence is lowest in these cases.
If the surgeon must 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, the 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 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.
Fibrin glue
Treatment with fibrin glue is currently the only non-surgical option for anal fistulas.
It involves the surgeon injecting a glue into the fistula while you’re under a general anesthetic. 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.
Risks of anal fistula surgery
Like any type of treatment, treatment for anal fistulas carries several risks.
The main risks are:
- Infection – this may require a course of antibiotics; severe cases may need to be treated in hospital
- Recurrence of the fistula – the fistula can sometimes recur 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.
All the procedures have different benefits and risks. You can discuss this with the surgeon about the potential risks of the procedure they recommend.
Many people do not need to stay in hospital overnight after surgery, although some may need to stay in hospital for a few days.