Classification

Classification

The most widely used classification of anal fistulae (Parks’) is based on anal gland sepsis in the intersphincteric space (the internal opening is at the dentate line); this results in a primary track whose relation to the external sphincter defines the type of fistula, which influences management ( Figure 80.29 ). The vast majority of fistulae are intersphincteric or trans-sphincteric. The American Gastroenterology Associ - ation classification ( Table 80.2 ), which condenses the Par ks’ classification into simple and complex fistula, is helpful in the decision to operate on clinical findings, investigate further or refer for specialist opinion. - /uni25CF /uni25CF /uni25CF /uni25CF - /uni25CF /uni25CF /uni25CF Intersphincteric fistulae (45%) do not cross the external sphincter (bar, for the purist, the most medial subcutaneous fibres running below the distal border of the internal sphinc - ter); most commonly they run directly from the internal to the external openings across the distal internal sphincter but may extend proximally in the intersphincteric plane to end blindly

TABLE 80.2 American Gastroenterology Association classi /f_i cation of anal /f_i stula. Simple /f_i stula Low (super /f_i cial or low inter- or low trans-sphincteric tract) Single external opening Complex /f_i stula High (high inter- or trans-sphincteric tract) Extra- or suprasphincteric tract Presence of abscess or collection Ano-vaginal /f_i stula Anal stricture

distal rectum at a second internal opening. Trans-sphincteric fistulae (40%) have a primary track that crosses both internal and external sphincters (the latter at a variable level) and that then passes through the ischiorectal fossa to reac h the skin of the buttock. The primary track may have secondary tracks arising from it, which often reach the roof of the ischiorectal fossa; they may rarely pass through the levator muscle to reach the pelvis. Circumferential (horseshoe) spread of sepsis may occur in the intersphincteric and pararec tal planes, as well as in the ischiorectal plane. Suprasphincteric fistulae (10%) run up to a level above the puborectalis and then curl downwards through the levators and ischioanal fossa to reach the skin. They are often caused by excessiv e probing of an abscess cavity or fistula tract during examination under anaesthesia. They are di ffi cult to distin guish from high-level trans-sphincteric tracks; however, the management strategies are similar. Extrasphincteric fistulae (5%) run without specific relation to the sphincters and usually result from pelvic disease or trauma.