Parks' classification of anorectal fistulas, anterior view

Parks described four types of anorectal fistulas that originate from cryptoglandular infections. Fistulas can have a complicated anatomy with one or more extensions and accessory tracts. The original Parks' classification did not include a superficial fistula tract.
Type 1 is an intersphincteric fistula that travels along the intersphincteric plane.
Type 2 is a transsphincteric fistula that encompasses a portion of the internal and external sphincter.
Type 3 is a suprasphincteric fistula that encompasses the entire sphincter apparatus.
Type 4 is an extrasphincteric fistula that extends from a primary opening in the rectum, encompasses the entire sphincter apparatus, and opens onto the skin overlying the buttock.