Role of Magnetic Resonance Imaging in Evaluation of Perianal Fistula

ABSTRACT

Introduction: Perianal fistula is an abnormal infected tract that connects the internal opening in the anal canal to the external opening in the perianal skin. It is an important cause of significant patient morbidity related to the lower intestinal tract. Magnetic resonance imaging (MRI) is the imaging modality of choice in the pre-operative assessment of perianal fistulas due to its excellent soft tissue resolution to accurately demonstrate the anatomy of the perianal region and the relationship of the fistulous tracts to the pelvic diaphragm and the ischiorectal fossae. Aims and Objectives: This study aims to assess the role of MRI in evaluation of perianal fistula and to correlate the imaging findings with post-surgical data. Materials and Methods: In this prospective study, 50 patients of all age groups with perianal fistulas were evaluated by MRI in the Department of Radiodiagnosis, Gandhi Medical College and Hamidia Hospital over a period of 1 year. MRI was performed on 1.5 Tesla Hitachi ECHELON SMART - 523 MRI machine using the required protocol and sequences. Fistulas were classified according to St James’s University Hospital MRI classification system and imaging findings were compared with post-surgical data. Results: MRI could detect the presence of fistula in all 50 patients, indicating 100% sensitivity. Most patients (68%) had internal opening on the posterior aspect of anal canal. Active fistulous tract was seen in 43 patients (86%) and chronic fibrosed tracts in 7 patients (14%). The most common type according to MRI grading was Grade I (54%), followed by Grade II (30%), Grade III (8%), and Grade IV (6%), respectively. MRI correctly described the type of fistula in 96% of cases. Conclusion: This study concludes that MRI proved as a valuable imaging modality in evaluation of perianal fistula and should always be performed in patients before surgery.