Parks et al developed a classification system for anal fistulas. The type of fistula may affect the best surgical approach. The authors are from St Mark's and London Hospitals in England.
Group
Type
Anatomic Features
intersphincteric
Type 1
fistula extends into the space between the internal and external anal sphincters
trans-sphincteric
Type 2
fistula extends across the intersphincteric plane and through the external anal sphincter into the ischiorectal fossa
supra-sphincteric
Type 3
fistula tracks along the intersphincteric to pass over the top of the puborectalis muscle; it then runs downwards through the levator plate to the ischio-rectal fossa with continuation to the skin surface
extra-sphincteric
Type 4
fistula runs outside of the external sphincter complex along its entire course; it passes from the rectum through the levator muscles to the ischio-rectal fossa with continuation to the skin surface
where:
• The intersphincteric fistula is the most common kind and may referred to as a "low anal" fistula.
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