Fistula

• A perianal fistula (fistula-in-ano) refers to an abnormal connection between the anal canal and the perianal skin.

  The majority are associated with anorectal abscess formation, with one third of patients with an anorectal abscess having an associated perianal fistula at the time of presentation.
• Inter-sphincteric is the most common type of perianal fistula

  • Passes through internal anal sphincter muscle and burrows out through the space between the internal and external sphincter muscles
• Aetiology:

  • Typically occurs as a consequence of an anorectal abscess
  • Inflammatory bowel disease - mainly perianal Crohn's disease
  • Diabetes
  • Trauma
  • Previous radiation to the area
• Clinical features:

  • Recurrent perianal abscess
  • Discharge per rectum - mucus, blood, pus or faeces
  • On examination an external opening on the perineum may be seen
  • A fibrous tract may be felt on DRE
• The majority of fistula's (not in an emergency setting e.g. abscess) are investigated initially with MRI
• Management:

  • Fistulotomy - laying the tract open by cutting through skin and tissue, allowing it to heal by secondary intention
  • Placement of seton (higher tract disease) - keep the tract open, drains any existing abscess as well as prevent recurrent formation of an abscess. Slowly move through the fistula, so may need to be changed every 4-6 weeks.
• Treatment is guided by the amount of sphincter muscle that is involved in the fistula tract as damage to this can cause bowel continence problems
• Setons for high tract disease:

  • Allows abscess to drain and settle inflammation
  • Can sometimes remove it and everything will close up behind it
  • Sometimes leave it in a long time for tract to epithelialize and then go and remove the tract surgically
  • Sometimes slowly tighten the seton so it slowly cuts through tissue allowing tissue to heal behind it - takes a long time