Table 1. The Parks system classification for anal fistulas.

Supralevator fistula could be present in grade I, II, or III. Translevator fistula could be present in grade II (IIb) or IV (IVa).

Grade	Description of the fistula	Characteristics
I	Intersphincteric	Ia: low; Ib: high extension in rectal wall without an additional high opening in the rectum; Ic: high extension in rectal wall with an additional high opening in the rectum; Id: no external opening in the perianal skin in the type Ib or Ic; Ie: high extension in pelvic cavity; If: pelvic disease draining into the perianal skin through the intersphincteric space
II	Transsphincteric	IIa: all fistulas below the puborectalis muscle; IIb: fistula with a branch going high in ischiorectal fossa (infralevator) or high through levator muscle (translevator) but not opening into the rectum
III	Suprasphincteric	Suprasphincteric fistula with or without a supralevator extension
IV	Extrasphincteric	IVa: transsphincteric fistula with a branch going high through levator muscle (translevator) but opening into the rectum (type IIb with an additional opening high in the rectum); IVb: extrasphincteric tract due to trauma; IVc: extrasphincteric tract due to anorectal disease like Crohn’s disease, ulcerative colitis, or carcinoma; IVd: pelvic disease draining into the perianal skin after piercing through the levator muscle