Anal fistula classification

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Manpreet Kaur, MD [2]

Anal fistula are classified into four types based on the relationship to sphincter– intersphincteric, transsphincteric, suprasphincteric, extrasphincteric. Anal fistula are classified into two categories based on the risk factors associated- simple anal fistula and complex anal fistula. Anal fistulas are also classified according to primary tracks into two- high and low anal fistulas.

Anal fistulas are classified into the four types based on the relationship to sphincter:^[1][2]

• Intersphincteric
• Transsphincteric
• Suprasphincteric
• Extrasphincteric

Anal fistulas are classified into two categories based on the risk factors associated:

• Simple anal fistula:^[3]
  • There are no risk factors associated with simple anal fistula.
  • Treatment of simple anal fistula results in low incidence of fecal incontinence and poor wound healing.
• Complex anal fistula:^[4]
  • There are many risk factors associated with complex anal fistula e.g preexisting incontinence, recurrent fistula, local irradiation, chronic diarrhea, or crohn’s disease.
  • There are multiple tracts found in complex anal fistula and is anterior in the location in females.

Anal fistulas are classified according to the position of primary tracks:^[5]

• Low fistula – In a low fistula close to the skin and the track passes through few or no sphincter muscle fibres.
• High fistulas– High fistula passes through multiple muscle fibers.

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