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Anal fistula

An anal fistula is a small channel that develops between the end of the bowel, known as the anal canal or back passage, and the skin near the anus.

An anal fistula is a small channel that develops between the end of the bowel, known as the anal canal, and the skin near the anus.

The end of the fistula can appear as a hole in the skin around the anus. The anus is the opening where waste leaves the body.

Anal fistulas are usually classed as either:

  • simple or complex – depending on whether there is a single fistula tract or interlinking connections
  • low or high – depending on its position and how close it is to the sphincter muscles (the rings of muscles that open and close the anus)

When should I see my GP?

The common symptoms of an anal fistula include:

  • skin irritation around the anus
  • a throbbing, constant pain that may be worse when you sit down, move around, have a bowel movement or cough
  • a discharge of pus or blood when having a bowel movement (rectal bleeding)

You should see your GP if you have any of these symptoms. You may be referred to a specialist in bowel conditions, known as a colorectal surgeon, for further investigation.

Read more about diagnosing an anal fistula.

What causes an anal fistula?

An anal fistula usually develops after an anal abscess (a collection of pus) bursts, or when an abscess has not been completely treated.

A fistula can also be caused by conditions that affect the intestines, such as inflammatory bowel disease (IBD) or diverticulitis.

An anal fistula affects:

  • as many as 50% of people with Crohn's disease
  • up to 30% of people with HIV (a virus that attacks the body's immune system)
  • approximately 30-50% of people with an anal abscess (this is slightly more common in women than men)

Read more information about the causes of an anal fistula.

Treating an anal fistula

Most anal fistulas require surgery because they rarely heal if they are not treated. Several surgical methods are available, depending on where the fistula is and whether it is classed as simple or complex.

You may be able to go home on the day of surgery. However, you may need to stay in hospital for a few days if the fistula is difficult to treat. 

Read more information about treating an anal fistula and recovering from anal fistula surgery.

There is a risk of complications after anal fistula surgery, including:

For example, after the most common type of surgery for a fistula (known as a fistulotomy), the risk of an anal fistula coming back is around 21%.

The risks vary depending on the type of procedure. You can discuss this with your surgeon.

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Anal fistula

To diagnose an anal fistula, your GP will look at your medical history and carry out a physical examination.

To diagnose an anal fistula, your GP will look at your medical history and carry out a physical examination.

If there are several fistula tracts (channels), further tests may be needed to determine their position.

Your GP will also pay particular attention to any history of anal abscesses or conditions that affect your bowels, such as Crohn's disease. These conditions can lead to an anal fistula developing.

You will usually be referred to a specialist in bowel conditions, known as a colorectal surgeon, for further investigation.

Physical examination

The specialist will examine your anus (the opening where waste leaves the body) and the surrounding area for any physical signs of a fistula. The opening of a fistula usually appears as a red, inflamed (swollen) spot, which often oozes pus.

If the opening of the fistula is found, the specialist may be able to work out where the path of the fistula lies. The path of the fistula can sometimes be felt as a hard cord-like structure beneath the skin.

Rectal examination

Your specialist may need to perform a rectal examination to find out where the internal opening of the fistula is and if there are any secondary tracts branching off it. 

A rectal examination involves placing a finger into your anus and then up into your rectum (back passage). The doctor's finger will be covered with a glove and lubricated with gel.

During the examination, the doctor may ask you to squeeze your sphincter muscles (the rings of muscles that open and close the anus) around their finger, to assess how well they are working.

This can help to determine what kind of treatment you need, or whether further tests are necessary.

Proctoscopy

Your specialist may also need to use a proctoscope (special telescope with a light on the end) to see inside your rectum.

They may also use a fistula probe, which is a tiny instrument inserted through the fistula.

These examinations may be performed under general anaesthetic, where you are asleep.

Further tests

If you have a complicated fistula with several branches, you may need further tests to determine the exact position of the fistula tracts. This will help guide the treatment you have.

Some further tests that may be recommended include:

  • anal endosonography (ultrasound) – this test uses high-frequency sound waves to create an image of the inside of your body, and is an accurate and frequently used way of locating the internal opening of a fistula
  • magnetic resonance imaging (MRI) scan – an MRI scan uses strong magnetic fields and radio waves to produce a detailed image of the inside of your body, and is often used in cases of complex or reoccurring fistulae
  • computerised tomography (CT) scan – a CT scan uses X-rays and a computer to create detailed images of the inside of your body; it may be used if you have an inflammatory bowel disease, such as Crohn's disease, as it can assess the extent of the inflammation
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Anal fistula

After having surgery to remove an anal fistula, you should be able to move around and eat and drink after the effects of the anaesthetic have worn off.

After having surgery to remove an anal fistula, you should be able to move around and eat and drink after the effects of the anaesthetic painkilling medication have worn off.

If the fistula is relatively simple to operate on, you may be able to go home on the same day as the surgery. However, if the fistula is complicated, you may need to stay in hospital for a few days or have further surgery to complete the procedure.

Looking after the wound

After the operation you will need to wear a dressing over the surgical cut until the wound has healed. Your dressings will need to be changed regularly and you will usually be shown how to do this at home. 

However, you may need to visit the hospital or GP surgery so they can check how the wound is healing or change the dressing for you. Most wounds take around six weeks to heal.

There may be some bleeding or a discharge from the wound for the first few weeks, particularly the first time you have a bath or go to the toilet.

You may wish to wear a pad, such as a sanitary towel, inside your underwear to avoid staining your clothes. This advice applies to both men and women.

You should see your GP if you have:

  • heavy bleeding
  • increasing pain, redness, swelling or discharge
  • a high temperature of 38ºC (100.4ºF) or over
  • nausea (feeling sick) or vomiting
  • constipation – being unable to empty your bowels for more than three days, despite using a laxative
  • difficulty passing urine

Washing

The following tips may help keep the area around the fistula clean and prevent infection or irritation:

  • use warm water and cotton wool to wash the skin, rather than a towel or sponge – pat the skin dry rather than rubbing it, or use a hairdryer on a low setting
  • avoid perfumed products and talcum powder as these can irritate the skin around the fistula
  • you may be prescribed a barrier cream, which can be applied to stop irritants reaching the skin

Medication

Painkilling medication

After the anaesthetic has worn off, you may need to take some pain relief medication.

Over-the-counter painkillers such as paracetamol or ibuprofen can normally be used, although you should check with your surgeon before using them. Always read the manufacturer's instructions.

A 15-minute bath may also help reduce the pain. The bath water should be as warm as you can comfortably sit in.

Laxatives

Laxatives are a type of medicine that can help you empty your bowels. You may be prescribed laxatives to make it easier for you to go to the toilet after your operation.

Antibiotics

You may be prescribed antibiotics (medication to treat infections caused by bacteria) to take before and after surgery. These will help reduce the risk of an infection. If you are prescribed antibiotics, make sure you complete the course.

Resting

You may need rest for a few days after your operation, but you should avoid sitting still for a long time. Also avoid doing too much walking.

When you are resting, the following tips may help make you more comfortable:

  • wear loose-fitting clothes and underwear
  • lie on your side when on the sofa or in bed
  • pillows or cushions may help make sitting more comfortable – some pharmacies sell cushions designed to relieve pressure when sitting

Returning to normal activities

You can return to work and start to do some gentle exercise when you feel able to.

Ask your surgeon for advice on when you can drive again. This is usually after a minimum of 48 hours.

You should not go swimming until the wound has completely healed.

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