Background: Successful surgery for perianal fistula is contingent upon accurate pre-operative classification of the primary tract and its extensions. We aimed to find, using "evidence based medicine" (EBM) methods, the optimal technique for fistula classification: MRI, anal endosonography (AES) or clinical examination.
Methods: A clinical question was derived, "In patients suspected of having perianal fistula, how does MRI compare to AES and clinical assessment for discriminating simple from complex disease".