The internal opening of an anal fistula is generally located at the site of inflammation in the anal crypt. The primary reason for the formation of an anal fistula is the repeated outbreaks at the anal crypt, which lead to further infection and the formation of a perianal abscess. When the abscess cavity ruptures, it forms an external opening and the anal fistula. Surgical treatment is required for the internal opening of an anal fistula, generally involving a seton procedure that threads a line through the internal opening and part of the sphincter muscle, gradually cutting and draining the area slowly. If the inflammation at the internal opening is significant, it may also be necessary to excise part of the infected site in the anal crypt. Post-surgery care of the internal opening of an anal fistula primarily involves dressing changes, requiring daily thorough disinfection of the local area, ensuring clear drainage, to allow the granulation tissue at the internal opening to grow freshly, and to slowly heal the wound without infection. (Medication should be taken under the guidance of a doctor.)