Magnetic resonance imaging in the management of fistula in ano

Fistula-in-ano is a common condition in which accurate diagnosis of the fistula track is essential as inadequate assessment and surgical treatment may lead to multiple unnecessary operations and may also render the patient incontinent. Several studies have suggested that Magnetic Resonance Imaging (MRI) can accurately identify the fistula track in relation to the sphincter complex. The aim of this study was to investigate the value of the routine use of completely non-invasive pre-operative MRI in patients with suspected fistula-in-ano. Each scan was reported by a consultant radiologist on two occasions to determine whether the radiologist's opinion had changed and/or become more accurate with further experience. Surgical assessment of the fistula was performed under general anaesthesia by one surgeon without knowledge of the result of the MRI scan. The results of the surgical assessment and the MRI scan were compared and the surgical procedure completed. Thirty three patients with a clinical diagnosis of fistula-in-ano were treated and 27 subsequently confirmed to have a fistula. MRI detected 42% of tracks, identified correctly on initial assessment which increased to 50% at the end of the study, 63% and 74% of internal openings, 33% and 46% of external openings and 50% and 33% of abscesses. These data suggest that there is a learning curve for radiologists undertaking MRI scanning for fistula in ano, this is probably because the pathology of fistula in ano and anatomy of the anal sphincter complex are relatively new to radiologists. Routine MRI scanning of patients with fistula-in-ano is not necessary but there may be a role for MRI in assessing complex or difficult fistulae.