An anal fistula is an abnormal connection from the anal canal (back passage) to the surface of the skin near the anus. The incidence of anal fistulas in Crohn’s Disease  is around 30% so it is quite common. Fistulas are much less common in people with Ulcerative Colitis.

Although the cause of anal fistulas in Crohn’s Disease  is unclear, active inflammation in the rectum increases the risk. Fistula symptoms include pain and the discharge of pus, blood or faeces from the skin openings. If a fistula develops into an abscess, symptoms may include pain, swelling and fever. An abscess needs emergency surgery.

Anal fistulas are considered as either low (simple) or high (complex), according to its relationship to the anal sphincter muscles. A high fistula is one that runs through a large amount of sphincter muscle, whereas a low fistula is one that runs through a small amount of muscle. For this reason, high fistulas are more difficult to treat because of the higher chance of damaging the sphincter muscle during surgery.

If you have a fistula you should consult a Colorectal Surgeon with expertise in fistula surgery. They will carry out an examination to confirm the diagnosis. It is probable you will need an MRI scan to investigate the fistula. Many patients also need to be examined under anaesthetic to more fully understand the nature of the fistula.

The treatment of anal fistulae will be different in each patient but will require a combination of drug therapy and surgery. All treatments aim to drain infection away, improve your quality of life and, where possible, cure the fistula.

Drugs for the treatment of fistulae

Antibiotics such as Ciprofloxacin and Metronidazole have been shown to improve fistulae symptoms. Although useful initially, these antibiotics rarely heal the fistula and symptoms often recur once stopped. Drugs such as Azathioprine or Mercaptopurine are commonly used but the introduction of drugs such as Infliximab and Adalimumab have significantly improved the management of anal Crohn’s disease. Indeed they are the current gold standard and frequently recommended by clinicians.

Surgery for treatment of fistulae

Surgical treatment is likely to be recommended, often in combination with drug therapy. The type of operation suggested will depend on the location and severity of the fistula. With complex fistulas, you may need more than one operation. With a simple fistula one of the most common operations is a fistulotomy.  In this, the infected tract is cut open. The wound created can take some time to heal but the success rate is the best of any of the surgical treatments (80-100%). Surgeons commonly don’t recommend this option in Crohn’s Disease if they feel that too much sphincter muscle will be cut during this procedure and hence cause problems with bowel control. There may also be concerns about wound healing in Crohn’s Disease.

With complex or high fistulas which involve the anal sphincter muscle, there can be more of a risk of incontinence if the fistula is cut open.  So, the surgeon may put in a ‘seton’.  This is a thread which is passed through the fistula and out through the anus as below.

The most common type of seton is a loose seton.  This allows drainage of any remaining infection and prevents abscess’s forming. The seton may be removed later or can remain in place for some time.  Another option may be a ‘cutting seton’.  Here the seton is gradually tightened over time, usually over a few months.  This makes the seton ‘cheesewire’ slowly through the muscle closing the fistula as it moves.

Other treatment options for anal fistulas may include fibrin glue, Collagen paste or plugs made of porcine (pig) tissue.  These techniques are about 50% successful. Research is currently looking at injecting the fistula with stem cells or Infliximab but more results are needed before this can be recommended routinely.

In a very small number of people a temporary stoma may be necessary. Rarely, an operation to remove the whole rectum may be recommended. This is major surgery and is not often necessary.

Diagrams © Neil Borley (www.gloshospitals.org.uk)