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Low versus high anal fistula

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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classification of anal fistula

Several classification systems of the condition have been described but the most useful and widely accepted classification is that described by Parks:

  • anal fistulas are classified according to the relationship between the primary fistula track and the analsphincter muscles into:

    • superficial fistula - track beneath the internal and external anal sphincters

    • intersphincteric fistula - between the internal and external anal sphincter muscles in the intersphincteric space

    • trans-sphincteric fistula - crossing both the external and internal anal sphincters

    • suprasphincteric fistula - travels outside the internal and external sphincters over the top of the puborectalis muscle and penetrates the levator muscle before tracking down to the skin

    • extrasphincteric fistula - outside the external anal sphincter and penetrates the levator muscle into the rectum

low versus high anal fistula

Fistulae are described according to the level at which they transgress the anal sphincters into"low" or "high"

  • low fistula
    • the internal orifice of the fistula begins below puborectalis
    • the track passes through few or no sphincter muscle fibres and is relatively close to the skin
    • e.g. - superficial fistulas, low intersphincteric fistulas, and low trans-sphincteric fistulas
    • these are relatively easy to manage (in the absence of complications or underlying conditions ) and pose little threat to continence.

  • high fistula
    • the internal orifice begins above puborectalis
    • a track that passes through or above a large amount of muscle; its route may be more complicated and further away from the skin
    • e.g. - high intersphincteric fistulas, high trans-sphincteric fistulas, suprasphincteric fistulas, and extrasphincteric fistulas
    • are much rarer than low fistulas, occurring in Crohn's disease, ulcerative colitis - more rarely, or as a result of a foreign body
    • management of a high fistula is more complex than that of a low fistula (1)


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