Rules for anal fistulas with scrotal extension

Objectives: To evaluate the rules for anal fistulas with scrotal extension, in particular, whether a high transsphincteric or suprasphincteric fistula, of which internal openings are usually located posteriorly, would extend into the scrotum. Methods: We retrospectively analyzed 446 consecutive male patients who underwent definitive anal fistula surgery. We compared fistulas with scrotal extension according to the location of the internal opening and divided them into anterior and posterior groups. Results: Forty-six (82.1%) of the 56 anal fistulas with scrotal extension had anterior internal openings. After excluding recurrent fistulas, 42 (87.5%) of the 48 anal fistulas with scrotal extension had anterior internal openings. The relative risk of scrotal extension in the anterior group was 14.22 times higher than that in the posterior group (95% CI: 7.43-27.21; p<0.0001). After excluding recurrent fistulas, this relative risk rose to 18.67 (95% CI: 8.18-42.58), (p<0.0001). Conclusions: Anal fistulas with scrotal extension are mostly low transsphincteric or intersphincteric with anterior internal openings. High transsphincteric or suprasphincteric fistulas rarely extend into the scrotum, except in recurrent cases.