Diagnostic accuracy of magnetic resonance imaging in detecting and grading perianal fistulas

Objective: To determine the diagnostic accuracy of magnetic resonance imaging (MRI) in detecting and grading perianal fistula, taking operative findings as gold standard. Methodology: This descriptive, cross-sectional study was conducted in department of Radiology & Imaging, Holy Family Hospital, Rawalpindi from 09-06-2019 to 08-12-2019. A total of 100 patients underwent MRI on 1.5 tesla GE machine using a pelvic phased array multicoil. Images were interpreted by experienced radiologist to identify and grade perianal fistula. After surgery, findings were recorded for presence/absence of perianal fistula as well as for anatomical details of fistulous tract. MRI findings were compared with operative findings. Data were analyzed using SPSS version 20.0. Results: MRI showed the presence of perianal fistula in 87 patients. Operative findings confirmed perianal fistula in 89 cases where as 11 patients revealed no perianal fistula. Overall sensitivity (Sn), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV) and diagnostic accuracy (DA) of MRI in detecting perianal fistula were 95.5%, 81.8%, 97.7%, 69% and 94%, respectively. The most common type of fistula was intersphincteric grade 1 fistula. Abscess formation was more common in grade 3, 4 and 5 fistulas. Internal opening of the fistulous track was most commonly identified posteriorly in midline at 6 O'clock position. Conclusion: MRI is a highly sensitive and accurate imaging modality for pre-operative diagnosis and grading of perianal fistula.