OBJECTIVETo investigate the epidemiology, internal opening location, and risk factors associated with recurrence of anal fistula.

METHODSClinical data of 1783 hospitalized patients admitted for anal fistula treatment to Shanghai Shuguang Hospital from January 2013 to September 2015 were retrospectively analyzed. Fistula passing through anorectal ring or locating above was defined as high anal fistula (n=125). Internal opening location was defined as follows: posterior (5 to 7 o'clock), front(11 to 1 o'clock), left (2 to 4 o'clock) and right (8 to 10 o'clock).

RESULTSAmong 1783 cases, 1526 were male with a median age of 36 years, 257 were female with a median age of 35 years, and the ratio of male to female was 5.9 vs 1.0. In high anal fistula cases, this ratio of male to female was 7.3 vs 1.0. Posterior internal opening accounted for 51.4%(884/1720), while this percentage was 66.4%(83/125) in high anal fistula cases, which was significantly higher than 50.2%(801/1595) in low anal fistula cases(P=0.002). Postoperative recurrence rate was 2.6%(45/1720) and the rates in high anal fistula and low anal fistula were 13.6%(17/125) and 1.8%(28/1595) respectively, with significant difference(P=0.000). Multivariate logistic regression analysis showed that fistula height(OR=5.475, 95%CI:2.230 to 13.445, P=0.000), treatment history(OR=2.671, 95% CI:1.315 to 5.424, P=0.007), seton placement history (OR=4.707, 95%CI:1.675 to 13.232, P=0.003) and concomitant colitis(OR=10.300, 95%CI:1.187 to 89.412, P=0.034) were independent risk factors for anal fistula recurrence. Seton placement history was an independent risk factor for high anal fistula recurrence (OR=6.476, 95%CI:1.116 to 37.589, P=0.037).

CONCLUSIONSAnal fistula occurs in young and middle-aged male patient. Internal opening locates in posterior more commonly, especially in high anal fistula patients. Postoperative recurrence rate of high anal fistula is quite high. Patient with both high anal fistula and seton placement history has significantly high rate of postoperative recurrence.