Anal fistulas (perianal fistulas)

What is an anal fistula?

A fistula is an abnormal tunnel between two organs in the body (such as the bowel and bladder). In an anal fistula a tunnel forms between the anal canal at the end of your colon and the skin around your anus (the part of your bottom where poo leaves).

They are also referred to as perianal fistulas, with peri meaning ‘around’.

What causes an anal fistula?

Most anal fistulas develop after an anal abscess that hasn’t healed or drained away properly. 

Anal abscesses can form when small glands inside the anus get clogged. This can cause an infection and an abscess can develop.

Certain things can make you more likely to develop an anal abscess or anal fistula. These include:

• Crohn’s disease
• Diverticulitis
• Hidradenitis suppurativa
• HIV
• Tuberculosis
• Complications from surgery near the anus
• Radiotherapy or chemotherapy cancer treatment

Less commonly anal fistulas can occur if you have ulcerative colitis and have had surgery to form an ileo-anal pouch.

One in every 2-4 people with an anal abscess go on to develop an anal fistula¹. 

Around a third of people with Crohn’s disease develop a fistula at some point in their life and around 3% of people with ulcerative colitis will get one².

Read more about the causes of an anal fistula

Different types of anal fistula and perianal fistula

Anal fistulas can be a single tunnel (simple fistula) or branch off into several tunnels (complex fistula). Some fistulas may form through muscles in your bottom which can be responsible for controlling your bowels.

Anal fistulas are given different names depending on where they are in relation to parts of the anal sphincter (the muscle that controls our bowel movements). These are:

• Intersphincteric
• Transsphincteric
• Suprasphincteric
• Extrasphincteric

The most common type is intersphincteric and the least common is extraphincteric.

What are the symptoms of an anal fistula?

Some of the common symptoms of an anal fistula include:

• Throbbing pain around your bottom that may get worse when you sit or move
• Swelling and redness around your bottom
• Fever and chills
• Feeling tired and sick
• Redness, soreness or itching of the skin around the anal opening
• Discharge coming out of the skin near your bottom. This discharge may be poo, blood or pus

Read more about the symptoms of an anal fistula

When should you go to the doctor for anal fistula?

If you have symptoms of an anal fistula you should speak to a doctor as soon as you can, especially if you know you’ve previously had an anal abscess.

This may be your general practitioner or a specialist consultant like a gastroenterologist if you are under their care for a condition such as Crohn’s disease.

How is an anal fistula diagnosed?

The doctor will talk to you about your symptoms and any relevant medical history, such as if you have Crohn’s disease or have recently had a known anal abscess.

They should also carry out a physical examination which will involve looking at the area around your bottom and your anus. They may press the area to see if it’s sore or if a discharge comes out and insert a finger into your bottom (anus) to see if they can feel anything.

If it’s thought you have an anal fistula then you may be referred for more investigations. Some of these may be done under general anaesthetic and can include:

• Proctoscopy - a camera inserted into your bottom to look inside your bowel
• Fistula probe - this is inserted through the outer opening of the fistula to investigate it
• Anoscope - a special device that’s inserted into your bottom to look inside your anal canal
• Pelvic MRI - images are taken in an MRI scanner to look at the fistula
• Endoanal ultrasound - an ultrasound scanner is inserted into your bottom to create an image of the muscles in the anal canal
• Fistulography - the fistula is injected with a contrast dye and then an X-ray is taken

Read more about how an anal fistula is diagnosed

How is an anal fistula treated?

Anal fistulas rarely go away by themselves so treatment will likely be necessary.

If your fistula is caused as a result of Crohn’s disease or ulcerative colitis then your anal fistula may be treated using medication, surgery or a combination of both.

These medicines may include:

• Antibiotics to help clear up any infection and reduce the discharge
• Biologic medications like infliximab or adalimumab. Ustekinumab or vedolizumab are other options

Some of the surgical options available include:

• Fisulotomy - this involves cutting along the length of the fistula and opening it out so it heals flat
• Seton suture - a piece of surgical thread is passed through the fistula and left in place for several weeks so that fluid can drain, helping it to heal
• Advancement flap procedure - the fistula is cut or scraped out while the hole on the inside is covered with a piece of tissue from inside the bowel
• Bioprosthetic plug - a plug made from animal tissue block the internal opening of the fistula
• Fistulectomy - the fistula is removed completely
• Ligation of intersphincteric fistula tract (LIFT) - the fistula tunnel is cut in two and both ends are stitched closed
• Video-assisted anal fistula treatment (VAAFT) - a telescope is used to look inside the fistula which is cleaned and then closed using an electric current

There aren’t many non-surgical options to treat an anal fistula. They currently include:

• Fibrin glue - glue is injected into the fistula and the fistula opening is stitched shut

What are the complications of an anal fistula?

If an anal fistula is left untreated they can be very painful and can lead to a bacteria infection which can cause sepsis. Sepsis can be life-threatening.

Complications after anal fistula surgery can include:

• The fistula returning
• An infection
• Being unable to control bowel movements if some of the muscles in the area (anal sphincter) are removed