[Magnetic resonance in the assessment of perianal fistula]

This study was aimed at investigating the effectiveness of Magnetic Resonance Imaging (MRI) in the diagnosis of perianal fistulas, by comparing imaging findings with those provided by rectal examination (RE) or surgery. The present data refer to 20 patients with anorectal fistulas in whom 24 main fistulous tracks were found. The fistulas were classified according to Parks and Kennedy's criteria, based on their relationship to the sphincters. In the 15 surgical patients, 15 of 17 fistulas were correctly identified by MRI (88.2%). In one case the submucous path of the fistula was missed, while another patient was misdiagnosed as having an intersphincter fistula which turned out to be a transphincter one at surgery. In the 5 non-surgical patients, only 4 of 7 MR-detected tracks were identified at RE. An intersphincter fistula was missed on rectal examination but demonstrated by both MRI and endoscopy. A suprasphincter track in a patient who was initially asymptomatic and thereafter developed a perianal abscess, was missed at clinics but became apparent on MR images. In one case anorectal examination underestimated the extent of the fistulous track, which was thought to be low while MRI demonstrated it to be high. Twelve abscesses were seen on MR images, all of them classified at surgery. One posterior pararectal suppurative collection in a non-surgical patient was apparent only at MRI. In our experience, in agreement with the latest literature reports, MRI has proved to be a very reliable method in the assessment of anorectal inflammatory diseases. We believe that MRI may play a valuable role in the preoperative assessment of the complex conditions causing a high risk of recurrence or anal incontinence as a result of inadequate treatment.