An anal fistula is a fistula formed when the rectum or anal canal communicates with the surrounding skin, also known as an anal fistula. It usually consists of a primary internal opening, a fistula and a secondary external opening, but there are also cases with only an internal or external opening. As shown in the figure, (this figure is a typical anal fistula) an external opening (white dot) can be seen at 3 cm from the anus, the internal opening is located inside the anus and is not visible, the fistula can be found during anal fingering, the fistula is located between the external and internal openings, and a cord can sometimes be palpated between the internal and external openings pointing to the anus. The treatment is mainly surgical.