Complex anal fistula is a fistula whose treatment with fistulotomy would expose the patient to an excessive risk of post-operative continence disorders. It is a challenge in proctological surgery because of the complexity of its therapeutic management in relation to the recurrences' frequency and the need to preserve sphincter function. Indeed, management is mainly based on fistulotomy techniques, but the latter expose patients to a significant alteration of their continence (less than 10% incontinence for simple fistulas but 30-50% for complex fistulas). In addition, these fistulas' management is constraining for patients due to the need for multiple interventions, long-term post-operative care and repeated discontinuation of activity.

Sphincteral saving techniques have therefore developed over the last three decades and have enriched the therapeutic panel of complex fistulas. They aim to block fistula pathways without risking altering sphincter function. In addition, their surgical consequences are often simple. However, they are associated with a greater risk of failure than after fistulotomy and sometimes disappointing to the point that some of these techniques have been gradually abandoned (biological glue and plug for example).

Among these sphincteral saving techniques, the investigators know the advancement flap, the injection of biological glue, plug's installation, the LIFT (Ligation of Inter sphincteric Fistula Tract), the clip's use but also, more recently a laser treatment, FiLaC™ (for Fistula Laser Closure), knowing that the idea was not new since the ND-YAG3 and CO24.5 lasers were already used in the treatment of anal fistulas, about twenty years ago, in experimental studies.

This technique consists of radiating 360° laser energy radially into the fistula path to "burn" it and causing thermal destruction by coagulation of the fistula wall ans granulation tissue2. It can bo offered to any type of fistula at risk on continence, including horseshoe extensions that can be treated at the same time. It is well suited for outpatient management because the postoperative period is simple and painless.

The literature is still poor on the subject with some studies published openly but the preliminary results are encouraging with a success rate of about 70%. No continence disorders reported.

A first retrospective study was conducted in the medical and surgical proctology department of the Hospital Group Paris Saint-Joseph on a cohort on 69 consecutive patients seen between May 2016 ans April 2017 and treated by FiLaC™ for a complex anal fistula. This technique has thus cured 60% of patients with superior trans-sphincter fistula. No incontinence-type complications were observed. These results, all the interesting as it was a learning phase, led the investigators to continue to use FiLaC™, which is currently practiced by all the team's practitioners as a first-line sphincter savings technique. The idea of this new work is to conduct an evaluation on a larger cohort of patients now that the investigators have more experience and it is being used routinely in the department at Groupe Hospitalier Paris Saint-Joseph.

Inclusion Criteria:

• Patient with complex anal fistula treated by the FiLaC™ between 05/01/17 and 05/01/18

Exclusion Criteria:

• Patient scheduled for treatment by FiLaC™ and collected as such but finally treated by fistulotomy given a fistula pathway considered intraoperatively less complex than expected
• Patient with recto vaginal or vaginal skin fistula
• Patient under guardianship or curators
• Patient deprived of liberty
• Patient objecting to the use of their data for this research

Patient with complex anal fistula treated by the FiLaC™ between 05/01/17 and 05/01/18