Frequencies of perianal fistula types using two classification systems.

Purpose: The aims of this study were to determine the frequencies of the perianal fistula subtypes according to the Parks and St. James's University Hospital (SJUH) classification systems and to evaluate the adequacy of these two systems for classifying and reporting perianal fistulas.
Materials and Methods: Magnetic resonance imaging examinations of 52 patients (44 men, 8 women) with perianal fistula were reviewed retrospectively. The fistulas were classified according to the Parks and SJUH classification systems.
Results: According to the Parks system, 13 patients had intersphincteric (25%), 36 had transsphincteric (69.23%), and 2 had (3.84%) extrasphincteric fistulas. Only one fistula (a subsphincteric fistula) (1.92%) could not be classified. According to the SJUH system, 10 patients had grade 1 (19.23%), 2 patients had grade 2 (3.84%), 13 patients had grade 3 (25%), 21 patients had grade 4 (40.38%), and 5 patients had grade 5 (9.61%) perianal fistulas. The one (and only) subsphincteric fistula was left unclassified.
Conclusion: The most common types are transsphincteric and intersphincteric fistulas. Although the two most commonly used classification systems are adequate for describing most perianal fistulas, there is a small percentage that is left unclassified.