Rationale: Perianal fistulas are a common, invalidating problem for which a more effective and widely applicable treatment is necessary. Vacuum therapy has become one of the main pillars for management of a wide variety of (chronic) wound healing problems. A novel catheter set was developed for vacuum therapy of perianal abscesses/sinuses and fistulas: The Semiflex Dome System. This system will allow for a better and faster treatment and it will offer conformability with various fistula shapes and sizes.

Objective: With this pilot study, the investigators aim to test our novel catheter set for vacuum therapy of perianal abscesses/sinuses and fistulas for feasibility and efficacy.

Study design: The design of this prospective, multicentre study is a feasibility study.

Study population: Patients (≥ 18 years) with (Crohn's) perianal fistulas and patients with perianal abscesses/sinuses are eligible.

Intervention: A tailored (length and diameter) Semiflex dome catheter is inserted under general anaesthesia, after 6 weeks of seton drainage in patients with a perianal fistula and right away in patients with a perianal abscess/sinus. The catheter is fixed on a Renasys Adhesive gel patch (Smith and Nephew) and is connected with a tubing system to a vacuum pomp with an average vacuum pressure of 80 cm H2O. After two - three days the catheter will be exchanged by a shorter catheter in the outpatient setting. The therapy is continued for a maximum of four weeks in patients with a perianal abscess/sinus and two weeks in patients with perianal fistulas.

Main study parameters/endpoints: The primary objective of the study is the feasibility of the methodology with respect to smoothness of insertion and changing the semiflex catheters, capability of proper fixation of the catheter and maintaining vacuum for more than 48 hours, and compliance to the therapy in terms of pain and discomfort. Secondary objectives are efficacy of drainage of the perianal abscess/sinus, efficacy of curing the perianal abscess/sinus in terms of complete collapse of the sinus and disappearance of induration, efficacy of management of perianal fistula in terms of clinical and radiological healing, and safety in terms of complications.

Nature and extent of the burden and risks associated with participation: The Semiflex Dome Catheter System will be placed in patients with perianal fistulas and perianal abscess/sinus who would otherwise be treated using prior-art passive drainage catheters or repurposed vacuum-assisted closure therapy sponges. There are no known additional risks stemming from the proposed therapy. The Semiflex Dome Catheter System is made entirely of medical-grade silicone certified with ISO 10993- 05 and ISO 10993-10. The catheters will be connected with a tube configured to be connected to a CE certified vacuum generating system.

Sample size: Since this is a pilot study no sample size is required. The pilot study will consist of 2 parts. In the first part, 10 patients in each study group will be included and it will be assessed per study group if the catheter meets the proof of principle. After a positive result in one or both study groups, the second part of the study will start. 10 patients in each study group will be included. The proposed treatment protocol is considered feasible if at least 70% of the Semiflex dome catheter treatment per study group meets the four primary objectives.

Inclusion criteria

• Perianal abscess/sinus or (Crohn's) perianal fistula
• ≥ 18 years and < 80 years
• Written informed consent

Exclusion criteria

• Patients with more than 2 external perianal openings
• Rectovaginal fistula
• Life expectancy < 2 years
• Dementia or altered mental status that would prohibit the understanding and giving of informed consent