Once an anal fistula is diagnosed, the only way to treat it is through surgery. A gland in the wall of the intestine about 1.5 cm inside the anus, called the anal sinus, becomes infected leading to a perianal abscess. After the abscess breaks down or the inflammation subsides some, a duct is formed called an anal fistula. The common clinical manifestation is a small hole outside the anus, which is flowing pus, called the external opening. But the root cause of the disease is an infected gland in the intestinal wall inside the anus, and once infected, it is equivalent to a small hole in the intestinal wall. The actual fact is that you will be able to get a lot more than just a few of these.