Anal fistula

What is anal fistula?
An anal fistula is a connection 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.

Anal fistulas are usually classed as either:

  • simple or complex – depending on whether there is a single fistula tract or many 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)
  • intersphincteric fistula – the fistula tract (channel) crosses the internal sphincter and opens on the surface of the skin next to the anus
  • transsphincteric fistula – the fistula tract passes through both the internal and external sphincters and opens on the surface of the skin next to the anus

What are the symptoms?

Symptoms include:

  • skin irritation around the anus
  • a throbbing, constant pain that may be worse on sitting down, moving around, or with a bowel movement or cough
  • a discharge of pus or blood
  • recurrent perianal abscesses, an abscess can also cause
  • a high temperature
  • fatigue
  • a general feeling of being unwell

If the fistula is caused by inflammation of the bowel (example Crohn’s disease )

  • abdominal pain 
  • diarrhoea
  • loss of appetite 
  • weight loss
  • nausea (feeling sick)
  • vomiting

What are the causes of an anal fistula?
The most common cause of anal fistula is an anal abscess
Anal abscess is a collection of pus near the anus. It usually develops after infection of glands inside the anus. Abscesses may be treated antibiotics but in most cases an incision and drainage of abscess is needed.
Fistulas often follow a diagnosis of anal abscess and a fistula often results from the abscess bursting onto the skin. The track of the fistula may depend on the path the pus takes to reach the skin. If it involves the muscles around the anal canal the resulting fistula is ofetn called a complex fistula.
An anal fistula can also be a complication of other conditions that cause the intestines to become inflamed. Crohn’s disease can often first present with anal fistula.

Other causes
Other conditions that can lead to the development of an anal fistula include:

  • cancer of the anus or rectum 
  • Infections like Tuberculosis, HIV and AIDS, chlamydia, syphilis

An anal fistula may also develop as a result of:

  • a growth or ulcer (painful sore)
  • a complication of surgery
  • a health problem you were born with

Diagnosis and management

Diagnosis of anal fistula will need a history taking and examination by an expert. Investigations may be needed to find the cause of the fistula and may involve colonoscopy. Other investigations including endoanal ultrasound and MRI pelvis may be rerquired to delineate the exact path of the fistula.

What is the treatment?

The only cure for an anal fistula is surgery. The type of surgery depends on the position of your fistula, whether it is classed as simple or complex and the expertise of the surgeon. The aim of surgery is to repair the fistula without damaging the sphincter muscles around the anal canal. Types of surgery include:
Fistulotomy, insertion of seton, LIFT (ligation of intersphincteric fistula track), fistula plug insertion and advancement flap.

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