Pre Surgical Imaging of Fistula in Ano

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Authors : Avni K P Skandhan


In 1976, Parks, Gordon and Hardcastle published their article entitled ‘A classification of Fistula- in ano.’ Their classification was based on the identification of four types of fistula: inter sphincteric, trans sphincteric, supra sphincteric and extra sphincteric. An intersphincteric fistula runs downwards between the internal and external sphincters. The trans sphincteric fistula runs from the intersphincteric space, through the external anal sphincter into the ischiorectal space. The supra sphincteric fistula runs upward between the internal sphincter and external sphincter and then bends around the pubo rectalis muscle and penetrates the pelvic floor, to traverse downwards through the ischiorectal fossa.

An extra sphincteric fistula passes through the external anal sphincter and then branches out into two tracks- one extending cephalad penetrating the pelvic floor and finally ending in rectum and the other extending caudally ending in the external opening. Although this classification does not take into account the circumferential extend of the disease it is widely used because of its simplicity. Another reason is that this classification relates the anatomical relation of the fistulous track to the anal sphincters which is relevant for the choice of treatment.  


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