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A perianal fistulous tract that arise at the right side at 7 o'clock of the anal canal. It penetrates the external anal sphincter at the midline posteriorly and divides into 2 branches at the intersphincteric level surrounding the anal canal. The right branch penetrates the posterior vaginal wall and communicates with the vaginal cavity while the left side branch ends in a collection. The vagina becomes filled with the injected contrast.