Distalization of perianal fistulas after loose silicone seton drainage is a myth

It is often stated that loose seton drainage results in distal migration of a fistula tract in perianal fistula. The aim of the present study was to assess this distalization of trans- and suprasphincteric perianal fistulas after a silicone seton has been inserted. Consecutive patients who underwent loose seton placement for the management of a transsphincteric or suprasphincteric fistula between January 2016 and December 2021 with a pre- and postoperative magnetic resonance imaging (MRI) were included in the present retrospective study. The height of the external anal sphincter (EAS) and the level of penetration of perianal fistula through the EAS or puborectal muscle (PRM) were determined on MRI. Primary outcome was migration of the fistula tract through the EAS and PRM. Thirty-eight patients with perianal fistulas were included. Median height of the EAS was 28 (IQR 25–34) mm before seton placement and 27 (IQR 24–33) mm afterward. Median level of perforation was 32 (IQR 17–40) mm before seton placement and 28 (IQR 17–40) mm afterward (p = 0.37). One fistula (3