What is anal fistula?

An anal fistula is a small channel that makes an abnormal connection between the end of the bowel and the skin near the anus. More often than not, anal fistulas start from an infection near the anus that causes a collection of abscess (pus) in the nearby tissue. The collection of pus then grows and stretches the skin or through lining of the anus. Thus a connection is formed between the skin and anus. Surgery to drain away the pus may also leave a small channel behind. This is known as anal fistula. An anal fistula may cause bleeding and discharge when passing motion and can be painful.

What causes anal fistula?

Most anal fistulas develop as a result of anal abscesses. Anal fistulas are formed as reaction to an anal gland that has a pus-filled infection (anal abscesses). They can occur if the abscess does not heal properly after the pus has drained away on its own.

A small number of fistulas are less frequently caused by other conditions such as Crohn’s disease, sexually transmitted diseases, tuberculosis, diverticulitis, cancer or a surgery near the anus. These affect your lower digestive tract or anal area and increases your risk of anal fistula.

Does an abscess always develop into a fistula?

No. However, if you have an anal abscess, you have around 50 per cent of the abscess developing into anal fistulas.

How do I know if I have anal fistula?

The end of the fistula may be visible as a hole in the skin around near anus, though it may be difficult for you to see it yourself.

Common symptoms of anal fistula include:

  • A constant and throbbing pain that may worsen when you move about, sit down, cough or have bowel movement
  • Skin irritation around your anus
  • Swelling or redness around your anus
  • Discharge of blood or pus when you go to the toilet
  • Fever


Do consult your doctor immediately if you have any of the symptoms above.

How is anal fistula diagnosed?

Your doctor will perform a physical and rectal examination for you to check for signs of an anal fistula. This is done by examining the skin around your anus and looking for an external opening in your skin. If it is possible, the depth and direction of your fistula tract will then be determined.

Otherwise, your doctor may use an anoscope, a special instrument which helps him see inside your anal canal. Further imaging tests such as ultrasound scan, CT scan or MRI scan may be used to provide images of the affected area for the doctor to diagnose.

Why is surgery recommended for anal fistula?

Anal fistulas cause unpleasant symptoms for the patient, pain and discomfort. In some cases, anal fistulas cause prolonged drainage. In other cases, where the exterior of the channel opening closes, there may be repeated anal abscesses. Anal fistulas do not usually get better on their own, and anal fistula surgery, known as fistulectomy, is necessary in most cases.

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