How the location of the internal opening of anal fistulas affect the treatment results of primary transsphincteric fistulas

Purpose The purpose of this study was to assess the influence of identification of the location of the internal opening of anal fistula on the recurrence rate after surgical treatment in patients with primary transsphincteric anal fistulas. The influence of preoperative rectal ultrasound on the treatment results was studied. Methods One hundred thirty-one patients operated in the period February 1992 to July 2005 were analyzed. Endorectal ultrasound (ERUS) was not performed (till February 2004) on 103 out of the 131 patients, while the other 28 received ERUS (from March 2004). We performed either cutting seton technique or fistulectomy according to the course of fistulous tract (high or low transsphincteric fistulas). The recurrence rate of anal fistula was assessed after the complete healing of the anal fistula after 6 months. Results In patients in whom ERUS was not performed, the internal opening was identified by endoscopy in 41.7% and in 47.6% intraoperatively. In patients in whom ERUS was preoperatively performed, the internal opening was identified in 85.8%. In all the studied groups, the internal opening of anal fistula was not localized in 13 patients (9.9%). Recurrence of the fistulas occurred in ten patients (7.6%); in seven out of 13 patients, the internal opening was not found (53.85%), and in three out of 118, the internal opening was identified (2.54%). Conclusions Relative risk of anal fistula recurrence was 20-fold higher in patients in whom the internal opening was not identified than in those with the internal opening identified. Preoperative ERUS doubled the identification rate and thus decreased the risk of recurrence.