Incidence of fistulas after drainage of acute anorectal abscesses

The aim of this study was to assess the incidence of anal fistulas and factors related to this incidence after incision and drainage of acute cryptoglandular anorectal abscesses. Of 170 patients without previous anal fistulas, 146 were followed up for an average of 99 (range, 22-187) months after abscess drainage or until a fistula appeared. Fifty-four (37 percent) patients developed a fistula, and 15 (10 percent) patients developed a recurrent abscess. The incidence of fistulas was higher in females than in males (50 vs. 31 percent; P = 0.0403), especially regarding anterior abscesses (88 vs. 33 percent). Abscesses growing Escherichia coli were more prone to fistula formation than those growing other bacteria (46 vs. 27 percent; P = 0.0368). Incision and drainage alone of acute anorectal abscesses is recommended, because an unnecessary primary fistulotomy can be avoided in more than half of the patients by this approach. For superficial anterior abscesses in females, however, primary fistulotomy may be considered.