Collagen Paste vs Mucosal Advancement Flap for FIA

• Clinical diagnosis of high cryptoglandular fistula-in-ano.
• Patients must have undergone a prior EUA to characterise the nature of the fistula.
• The fistula tract should be ≥ 2 cm in length.
• Only a single internal fistula opening should be present at EUA, such that the fistula is suitable for treatment by insertion of a seton drain.
• Patients must have been treated with a draining seton for a minimum period of 6 weeks prior to randomisation.
• Patients must be aged ≥ 18 years and able to provide informed consent.
• Fistulas must be of cryptoglandular aetiology.

Exclusion Criteria:

• Unable/unwilling to provide informed consent.
• Contraindication to general anaesthesia or spinal anaesthesia.
• Low trans-sphincteric fistulas.
• Non-cryptoglandular fistulas (e.g. Crohn's disease, obstetric, irradiation, malignant, etc.).
• Other perineal fistulas (e.g. rectovaginal fistulas, pouch-vaginal fistulas, etc.).
• Complex disease in which more than one internal fistula opening is present and requiring concurrent insertion of more than one fistula plug.
• Clinical evidence of active perianal sepsis. In the event that there is disagreement between clinical and radiological assessment of active sepsis/collection, the clinical opinion will prevail.
• Cultural or religious objection to the use of pig tissue.
• Absolute contraindication to magnetic resonance imaging (MRI) (e.g. cardiac pacemaker).
• Patients with recurrent anal fistulas previously treated with a fistula plug.