MR Imaging of fistula in ano: indications and contribution to surgical assessment

Background : Magnetic Resonance Imaging (MRI) is the imaging modality of choice for fistula in ano. The purpose of this study was to analyse the use of MRI, and to assess its contribution towards the assessment of this sometimes difficult condition. Methods : A retrospective analysis of all patients with fistula in ano between January 2003 and December 2007 was performed, focussing on those who had MRI assessment. The primary pathology, indication for MRI and the contribution of this investigation to assessment of fistula in ano were analysed. Results : MRI was performed in 40 patients. The primary pathologies included : perianal sepsis in 20 (50%), Crohn's disease in 11 (27.5%), primary fistula in ano in 6 (15%) and others in 3 (7.5%) patients. Indications for MRI were to assess the fistula anatomy in 17 (42.5%), to assess a clinically suspected fistula in 12 (30%), to assess a complex fistula found at Examination Under Anaesthesia (EUA) in 6 (15%) and to exclude a fistula in 5 (12.5%). MRI was considered helpful in 34 (85%) of all cases. MRI established the fistula anatomy and guided further surgery in 47.1%, correlated with EUA findings in 38.2% and excluded a suspected fistula in 14.7% of these. Conclusions : This study further supports the benefit of using MRI to assess fistula in ano. When used in selected patients, it was of benefit in 85% of cases, by establishing fistula anatomy and guiding further surgery, correlating EUA findings or excluding a clinically suspected fistula.