A new concept of the anatomy of the anal sphincter mechanism and the physiology of defecation. VII. Anal fistula: a simplified classification.

The pathology of anal fistulas was studied in 300 patients and a simple classification is put forward. Two main types of fistula are recognized: intrasphincteric and extrasphincteric, according to the relation of the track to the external sphincter. All fistulas start as a central space infection which either remains confined to the intrasphincteric compartment or spreads extrasphincterically. Intrasphincteric fistulas include both central and intersphincteric fistulas. The latter fistula, as well as the extrasphincteric, are either low or high according to the relation of the track to the levator plate. The classification is simple and practical. It clearly demonstrates the precise anatomic position of fistulas as related to anal musculature so proper planning for the treatment can be safely achieved.