1. Gordon P. Anorectal abscesses and fistula-in-ano. In: Gordon PH, Nivatvong S, editors. Principles and practice of surgery for the colon, rectum and anus. St. Louis: Quality Medical Publishing; 1999. p. 241–86.
2. Parks AG, Gordon PH, Hardcastle JD. A classification of fistula-in-ano. Br J Surg. 1976;63:1–12.
3. Williams JG, Farrands PA, Williams AB, et al. The treatment of anal fistula: ACPGBI position statement. Colorectal Dis. 2007;9 Suppl 4:18–50.
4. Coloproctology 23;F Stelzner,2001
5. Buchmann P, Alexander-Williams J. Classification of perianal Crohn’s disease. Clin Gastroenterol. 1980;9:323–30.