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Fistula In Ano

  • It is a track lined by granulation tissue which connects perianal skin superficially to anal canal or rectum deeply.

  • It usually occurs in a pre-existing anorectal abscess which burst spontaneously.


According to whether the internal opening is below or above the anorectal ring:
  • Low-level fistulae- Open into the anal canal below the anorectal ring.

  • High-level fistulae- open into the anal canal at or above the anorectal ring.

Anatomical classification (standard)
  • Subcutaneous

  • Submucous

  • Low anal

  • High anal and

  • Pelvirectal 

Park’s classification

  • Intersphincteric 

  • Trans-sphincteric (maybe high or low) and

  • Supralevator 

Clinical features
  • It presents with seropurulent discharge, along with skin irritation and one or more external opening may be present with induration of the surrounding skin.

  • Pain is not  a symptom as long as the opening is large enough for the pus to escape. But if the orifice is occluded pain increases until the discharge erupts.

  • Often it may heal superficially but pus may collect beneath forming an abscess which again discharges through same or new opening. Thus there may be two or more external openings, grouped together on the right or left of the midline, but when both ischiorectal fossas are involved then the opening is seen on each side which often intercommunicates.

Fistula In Ano

Goodsall’s rule
  • Fistulas with an external opening in relation to the anterior half of the anus is of direct type.

  • Fistulas with external openings in relation to posterior half of the anus, has a curved track may be of horse-shoe type, opens in the midline posteriorly and may present with multiple external opening all connected to a single internal opening.

Goodsall’s rule
Digital examination:

  • Internal opening can be felt as a nodule on the wall of the anal canal.


  • May show the internal opening of the fistula.
  • A hypertrophied papilla is suggestive that the internal orifice lies within the crypt related to the papilla.

Probing: not advisable


Low level fistulas:

  • Under G/A or spinal anaesthesia
  • Probe is passed through external opening up to the internal opening which is felt as an induration.
  • Fistula is opened along the probe using a knife.
  • Fibrous track along with unhealthy granulation tissue and additional external openings are excised.
  • Specimen is then sent to HPE

High level fistulas:

Surgery involves staged procedure:

Initial colostomy followed by definitive procedure. This prevents sepsis ans promotes faster healing.
Later closure of colostomy is done.

  • A slik or linen ligature is passed across the fistula and left in place with a tie.
  • This allows the fistula to granulate and heal from above and to close completely. 
  • Takes longer duration to heal.


  1. Pain is not a symptom as long as the opening is large enough for the pus to escape. But if the orifice is occluded pain increases until the discharge erupts.

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