To determine whether an anal fistula is severe, it mainly requires a digital rectal examination and probe inspection, and if necessary, supplemented with perianal ultrasound and pelvic MRI. If it is a low-lying single fistula tract, it generally is not severe and considered a low-type fistula. If the internal opening of the fistula is positioned high, or if there are multiple branches of the tract, the condition is generally more severe, classified as a high, complex fistula. Typically, the local infection will spread across the sphincter muscles, and some even reach the ischioanal fossa. Whether it is a simple low fistula or a high, complex fistula, once discovered, it requires prompt surgical treatment with fistulotomy and seton placement.