The presence of ano-perineal lesions (APL) in Crohn's disease is common and represents a major burden for the patient. More than one-third of patients with Crohn's disease will develop at least one ano-perineal lesion during the course of their disease. The cumulative incidence of APL is approximately 30% at 10 years and 43% at 20 years, regardless of the type of APL.

The appearance of ano-perineal lesions represents an important phase in the progression of Crohn's disease, but they have been little studied to date. There is little consensus regarding their overall management. Indeed, their management is difficult due to their destructive and recurrent nature, and their significant impact on patients' quality of life, continence, and sexuality is significant. The presence of ano-perineal lesions at the time of diagnosis, especially in young patients, is a poor prognostic factor.

Currently, magnetic resonance imaging is the gold standard for diagnosing anoperineal lesions in Crohn's disease. It allows for precise mapping of lesions, and its safety allows for repeated use. MRI is therefore highly effective for diagnosis and can also highlight lesions not identified during clinical examination.

Therapeutic objectives for Crohn's disease are changing, and a new "treat-to-target" strategy is emerging in the guidelines. It consists of closely monitoring clinical symptoms and endoscopic lesions to achieve complete remission. The occurrence of anoperineal lesions has been studied, and relapse is common under anti-TNF alpha therapy. It is conceivable that the treatment of anoperineal lesions could follow the same strategy. However, the role of MRI in monitoring ano-perineal lesions is poorly codified. A Rouen study investigated the feasibility of MRI for the study of ano-perineal lesions and assessed the clinical benefit of anti-TNF treatment in APL due to Crohn's disease, which was associated with a significant improvement in the Van Assche score, particularly T2 hyperintensity, a sign of perineal Crohn's disease activity. The disappearance of contrast enhancement was associated with remission. In 2017, follow-up of these APL patients treated with anti-TNF therapy found twenty-six patients in clinical remission, and 16 of the 26 had a normal MRI, defined by the absence of contrast enhancement or T2 hyperintensity.

The radiological evolution of ano-perineal lesions is also poorly understood. MRI monitoring of anoperineal lesions will be a determining element of the future "Treat-to-target" strategy, in the context of the emergence of new biotherapies and other treatments. Among the anti-TNF agents used in Crohn's disease, only infliximab has been specifically evaluated in anoperineal lesions. (15) Another anti-TNF agent used, adalimumab, has been poorly evaluated.

Data regarding the efficacy of other monoclonal antibodies such as vedolizumab (anti-integrin antibodies) and ustekinumab (anti-IL12 and IL23 antibodies) are currently limited. The main objective of the study is to describe the radiological evolution of patients with Crohn's disease, with fistulizing anoperineal lesion, treated with biotherapy.

Inclusion Criteria:

• All adult patients, monitored at the Rouen University Hospital for Crohn's disease, complicated by fistulizing anoperineal lesion, treated with Biotherapy, having benefited from an MRI at the start of treatment and during follow-up.

Exclusion Criteria:

• Minor patients
• Patients with an anoperineal lesion, without Crohn's disease
• Patients who have received surgical treatment with a stoma for perineal disease

Tous les patients majeurs, suivis au CHU de Rouen pour une maladie de Crohn, compliquée de lésion ano-périnéale fistulisante, traités par Biothérapie

The data provided will be the property of the sponsor and will be used solely for its own research activities.