Surgical diagram of fistula occlusion with the internal sphincter flap. (A) A suprasphincteric anal fistula is identified with IO located at 6 o'clock. (B) A segmented processing technique consists of the fistulectomy in the ischiorectal fossa and ends at the lateral of the external sphincter, resection of IO and the internal sphincter underneath, and curettage of the fistula in the intersphincteric space and external sphincter. (C) Ligation or suture is conducted to close the tract that went through the external sphincter, and an internal sphincter flap is prepared for the coverage. (D) Flap occlusion is accomplished with continuous barbed suture, followed by the closure of the intersphincteric space. IO = internal opening.