Anal Fistula

In this article

What is an anal fistula? What are the symptoms of an anal fistula? Why do you need specialist's advice? How does the anal fistula occur? Treatments for an anal fistula Fistulotomy Seton Insertion Advancement flap procedure LIFT procedure Bioprosthetic plug Permacol - collagen paste injection Risks of anal fistula surgery

What is an anal fistula?

An anal fistula is a small abnormal tunnel that develops between the end of the bowel (rectum and anal canal) and the skin near the anus. Anal fistulas can cause unpleasant long standing symptoms, such as discomfort, pain and skin irritation, and won't usually get better on their own. Surgery is necessary in most cases.

What are the symptoms of an anal fistula?

  • Small pustules that comes and goes from time to time causing various symptoms such as pus discharge, pain, bleeding. These may disappear on its own or with antibiotics but only to reappear later on
  • These also cause skin irritation around the anus
  • A constant, throbbing pain that may be worse when you sit down, move around, have a bowel movement or cough is a common symptom of a infective exacerbation of a fistula
  • Swelling and redness around your anus and a high temperature (fever) is commonly seen if you also have an abscess
  • Smelly discharge from near your anus
  • Passing pus or blood when you poo
  • 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

Why do you need specialist's advice?

Anal fistula is best treated by a specialist. Its a complex disease and only a specialist will be able to properly assess and plan the treatment. Improper treatment can cause serious and permanent harm. See your surgeon if you have persistent symptoms of an anal fistula. Your symptoms and your bowel functions will be assessed. Then your anus and the rectum will be examined. You will also need a colonoscopy. Sometimes more specialised tests such as Endo-anal Ultrasound scan or magnetic resonance imaging (MRI) scans will be necessary.

How does the anal fistula occur?

  • A vast majority of the anal fistulae cases will not have a clear cause. They develop after an anal abscess. They can occur if the abscess doesn't heal properly after the pus has drained away. It's estimated that between one in every two to four people with an anal abscess will develop a fistula.
  • 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 almost never heal if left untreated. In-fact they can cause serious complications if not properly treated. The aim of surgery is to heal the fistula while minimising  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 best option for you will depend on the cause of the fistula, 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 (EUA - Examination under anaesthesia).


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 (healing rate - >95%), although it's usually only suitable for fistulas that don't pass through much of the sphincter muscles, as the risk of incontinence is lowest in these cases.

If your surgeon has to cut a small portion of anal sphincter muscle during the procedure, they will make every attempt to reduce the risk of incontinence. In cases where the risk of incontinence is considered too high, one of the procedures below may be recommended instead.

Seton Insertion

If your fistula passes through a significant portion of anal sphincter muscle or if your fistula has many branches or if your fistula is having infective complications, your surgeon may initially recommend inserting a seton.

A seton is a piece of surgical thread that is 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 don't cure them.

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 (50% or less), but avoids the need to cut the anal sphincter muscles.

LIFT procedure

The ligation of the intersphincteric fistula tract (LIFT) procedure is a relatively new treatment for anal fistulae. It's designed as a treatment for fistulas that pass through the anal sphincter muscles, where a fistulotomy would be too risky.

During the treatment, a cut (incision) is made in the skin above the fistula and the sphincter muscles are moved apart. The fistula is then sealed by ligating at both ends and then divided.

This procedure has had some promising results so far, and the success rates are around 50-60%. This can be done for fistulae with a certain pathway only.

Bioprosthetic plug

Another option in cases where a fistulotomy carries a high risk of incontinence is the insertion of a bioprosthetic plug.

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

Some studies have suggested this may be an effective treatment for anal fistulas, but success rats vary widely from 5% - 60%.

Permacol - collagen paste injection

Treatment with Permacol is currently the only non-surgical option for anal fistulae. It involves your surgeon injecting a special collagen paste into your fistula while you're under a general anaesthetic. The paste helps seal the fistula and encourages it to heal.

It's generally much 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 don't need to be cut.

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; 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.