Anal fistula, commonly known as “rat stealing feces”, is a condition in which the anal canal or rectum is connected to the outside of the anus through a tube, and fecal matter and fecal fluid can be discharged outside through the tube instead of through the anus. In addition to dampness and itching, there is also pus flowing out of the ducts after infection, which can be painful when the pus is discharged and relieves the pain when the pus is discharged. If left untreated for a long time, the infection may recur and cause multiple fistulas around the anus to break down. The cause is mainly constipation, diarrhea, eating a spicy diet and other factors that cause the infection inside the anus to become abscesses, which protrude next to the anus and form an anal fistula when the abscesses break down. The specific cause is still unclear, but the unified view in the literature is that it is caused by long-term inflammation and repeated stimulation, with mucinous adenocarcinoma being the most common cause.