Loose Seton Prior to Surgery for Single-tract Cryptoglandular Fistula vs no Seton: a Multicenter Randomised Study

Cryptoglandular anal fistulas are a burdensome and often recurrent condition that can substantially affect quality of life and lead to prolonged treatment trajectories. In patients with a single-tract mid-high or high cryptoglandular anal fistula, treatment is commonly aimed at closure of the fistula while preserving continence. In current practice, many patients first undergo placement of a loose seton before definitive sphincter-preserving surgery. This staged approach is widely used in daily practice, but high-quality evidence supporting a benefit of routine preoperative seton placement is limited. Retrospective data suggest that preoperative seton drainage may not clearly improve outcomes before definitive repair. Because seton placement adds an additional procedure, may prolong treatment, and may increase patient burden and healthcare costs, a randomized trial is needed to determine whether this step can be safely omitted.

The SETON trial is a multicentre, randomized, controlled, non-inferiority trial with an integrated cost-utility analysis. The trial compares two accepted treatment strategies for patients with a single-tract non-purulent mid-high or high cryptoglandular anal fistula. In the intervention group, participants undergo loose seton placement using a non-cutting silicone vessel loop, followed by definitive sphincter-preserving surgery after approximately 8 weeks. In the comparator group, participants proceed directly to definitive sphincter-preserving surgery without prior seton placement. The definitive sphincter-preserving procedure is selected by the treating surgeon according to local practice and anatomical characteristics of the fistula and may include advancement flap (MAF), ligation of the intersphincteric fistula tract (LIFT), or laser ablation of the fistula tract (LAFT). The planned treatment method is recorded before randomization and used as a stratification factor.

Eligible participants are adults aged 18 years or older with a single-tract non-purulent mid-high or high cryptoglandular anal fistula. Key exclusion criteria are anorectal abscess, multiple or complex anorectal fistulas, inflammatory bowel disease or clinical suspicion requiring further investigation, history of anorectal malignancy, immunosuppressive medication use at the time of surgery, history of pelvic radiation, and pregnancy or lactation. Participants must also be able to complete Dutch-language questionnaires sent by email.

After written informed consent and baseline data collection, participants are randomized in a 1:1 ratio through the secure web-based Castor EDC system. Randomization is stratified by participating centre and by planned sphincter-preserving treatment method to promote balance between treatment arms. Because the two treatment pathways are visibly different, the trial is unblinded for participants and treating surgeons. Consecutive eligible patients are recruited at participating Dutch centres. Trial participation adds limited burden beyond standard care, mainly informed consent and follow-up assessments.

The primary outcome is successful fistula closure at 26 weeks after final surgery. Fistula closure is defined as absence of an external opening or discharge on physical examination and is confirmed by MRI or endoanal ultrasound when clinical uncertainty remains. Secondary outcomes include postoperative complications, need for re-intervention, pain intensity, time to return to work, continence assessed with the Vaizey score, fistula-related quality of life assessed with the FIQL, generic quality of life assessed with the EQ-5D-5L, patient-reported anorectal symptoms measured with proctoPROM, and healthcare and societal costs. Outcomes are reported in line with the Anal Fistula Core Outcome Set.