 Fistulas are usually divided into two groups. The first group contains fistulas called simple, which are intersphincteric fistulas or trans-sphincteric involving only the lower third of the sphincter complex. Fistulas usually didnt affect any muscle. The second group contains fistulas called complex. These are intersphincteric, trans-sphincteric, or even suprasphincteric, extrasphincteric fistulas. 