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Anal Fistula: Causes and Treatment

Anal fistula is a small tunnel or tract that develops between the anal canal (last part of the large intestine) and the skin around the anus.

Anal Fistula: Causes and Treatment


Most cases of anal fistula occur as a complication of an anal abscess. Infections in an anal gland can result in abscess formation in some cases. After the abscess drains spontaneously or after surgical drainage through the skin next to the anus, there can be a tunnel formation under the skin connecting the external surface to the anal canal.

Other less common causes:

  • Crohn’s disease – A long-term inflammatory bowel disease.
  • Large intestinal diverticulitis – Infection in diverticula, which are small pouches that bulge out of the intestine.
  • Sexually transmitted diseases – Sexually transmitted infections involving the anal canal can cause abscess formation and subsequently result in fistula formation.
  • Complication of surgery around anus – Surgeries around the anus can result in the formation of tract/s that communicates with the external surface.
  • Infections such as tuberculosis or HIV
  • Rectal cancer – Fistulas can form as a complication of rectal cancer


The symptoms of anal fistula can include:

  • Pain. A constant throbbing pain which may worsen on sitting, walking, coughing or during defecation
  • Skin irritation. Itching of the skin around the anus
  • Redness and swelling around the anus may be noted if abscess is present
  • Discharge. Smelly discharge around the anus
  • Pus or blood in the stools
  • Bowel incontinence. Difficulty in controlling bowel movements may be present in some cases.
  • Skin opening. The opening of the fistula on the skin around the anus may be visible, but it may be difficult for the person to see this.


Based on your symptoms, your doctor will suspect a diagnosis of anal fistula and perform a physical examination of the rectum and anus.

  • Digital rectal examination. A lubricated, gloved finger will be inserted into the anal canal after applying a local anaesthetic to relax the sphincter. Sometimes an instrument called anoscope may be inserted to get better visibility.
  • Proctoscopy. A particular metal or plastic instrument is inserted to view the rectum and the anal canal.
  • Imaging tests. Such as ultrasound scan, magnetic resonance imaging (MRI) scan, or computerised tomography (CT) scan can help in delineating the pathology.


Surgery is needed for definitive treatment of anal fistulas. They do not usually heal if left untreated.

  • Fistulotomy:  The fistula is cut open the entire length, and allowed to heal as a flat scar.
  • Seton procedures – A Seton (drain) is a surgical suture or a piece of rubber which is placed in the fistula, and the ends of which are brought together and secured forming a ring around the anus. The Seton is left in place for few months to provide controlled drainage, which allows the inflammation to reduce and form a solid tract of the scar.
  • Other procedures– A special plug or glue is used to fill the fistula tunnel, or a flap of tissue is used to cover the fistula.


The surgical procedures done for fistula treatment can be associated with early and delayed postoperative complications:

Early postoperative complications:

  • Retention of urine
  • Bleeding
  • Impaction of faeces

Delayed postoperative complications:

  •  Recurrence
  • Incontinence of stools
  • Narrowing of anus (Anal stenosis)
  • Delayed healing – Wound not healing even after 12 weeks of surgery

Next Steps

If you have any symptoms of anal fistula, visit your doctor. They may ask about your symptoms and other bowel conditions and manage accordingly.

Red Flags

If you have symptoms due to anal fistula and the pain is very severe, the cause of anal fistula may be attributable to complications other than abscess formation such as cancer or Crohn’s disease. If you have other symptoms such as abdominal cramping, bloating, early satiety, or weight loss there is a high chance of conditions such as inflammatory bowel disease or malignancy.

Consult a top Proctologist

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  • Poggio JL. Fistula-in-Ano. Accessed at http://emedicine.medscape.com/article/190234-overview on 15 June 2016.
  • NHS choices. Anal Fistula. Accessed at http://www.nhs.uk/Conditions/Anal-fistula/Pages/Introduction.aspx on 16 June 2016. I
  • nternational Foundation for Functional Gastrointestinal Disorders, Inc. (IFFGD). Other disorders – Anal Fistulas. Accessed at http://iffgd.org/other-disorders/anal-fistulas.html on 16 June 2016.
  • The American Society of Colon and Rectal Surgeons (ASCRS). Diseases and conditions – Abscess and Fistula Expanded Information. Accessed at https://www.fascrs.org/patients/disease-condition/abscess-and-fistula-expanded-information on 15 June 2016.

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