Parks Classification of Perianal Fistulas
 • Superificial (Simple) - Superficial fistula w/o crossing any sphincter or muscular structure
 • Intersphincteric (Simple) - Fistula tract b/w internal anal sphincter and external anal sphincter → in intersphincteric space
 • Trans-Sphincteric (simple if low, complex if high) - Fistula tract crosses the external anal sphincter
 • Supra-Sphincteric (complex) - Fistula tract penetrates the intersphincteric space and continues over the top of the puborectalis → penetrates the levator muscle before reaching the skin
 • Extra-Sphincteric (complex) - Fistula tract outside the external anal sphincter  → penetrating the levator muscle

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