Le cancer du canal anal est un cancer viro-induit en augmentation de type histologique essentiellement ??pidermo??de. L???IRM du canal anal est compl??mentaire de l?????chographie endo-anale et l???examen clinique pour le staging initial du cancer anal. L???IRM est r??alis??e avec des s??quences T2 et T1 inject??es dans des plans propres ?? l???orientation du canal anal. La classification initiale des l??sions s???effectue selon le syst??me TNM??: le staging T repose sur le degr?? d???infiltration tumorale avec la mesure pr??cise de la tumeur et la description de ses rapports avec les ??l??ments anatomiques de voisinage notamment l???envahissement des sphincters. Le staging N repose sur la visualisation d???ad??nopathies p??rirectales, iliaques internes, et inguinales. L???IRM a un int??r??t pronostique initial mais est aussi utile pour suivre les patients apr??s le traitement par radio-chimioth??rapie. L???int??r??t des s??quences fonctionnelles (diffusion, perfusion) dans le bilan initial et dans le suivi est encore en cours d?????valuation. Les examens de suivi afin de d??tecter une ??ventuelle r??cidive seront r??alis??s selon un protocole identique au bilan initial. La r??ponse au traitement peut-??tre compl??te avec une diminution du volume tumoral qui perdure plusieurs mois apr??s l???arr??t des traitements.

The anal canal cancer is a virally induced cancer, mainly of epidermoid type and its incidence is rising. MRI of the anal canal is complementary to endorectal-ultrasonography and clinical examination for the initial evaluation of anal cancer. MRI is performed with T2-weighted and T1-weighted contrast-enhanced sequences into plans related to the orientation of the canal. The initial classification of the lesions is made according to the TNM system: T staging is based on the degree of infiltration of the tumor with an accurate measurement of the tumor and the relationship with the adjacent structures. N staging is based on visualization of peri-rectal, iliac internal, and inguinal lymphadenopathy. The MRI has an initial prognostic interest but is also useful for the follow-up of patients after treatment by radio chemotherapy. The usefulness of the functional sequences (diffusion, perfusion) in the initial evaluation and monitoring is still under assessment. Follow-up examinations to detect a possible recurrence will be carried out according to the same protocol as the initial evaluation. The response to treatment could be complete with a reduction of tumor volume, which last several months after the end of treatment.