Magnetic resonance imaging classification of perianal fistula and its surgical correlation: a prospective observational study

Background: Perianal fistula is a common anorectal disorder characterized by chronic infection and abnormal communication between the anal canal and perianal skin. Successful treatment depends on complete identification of the primary tract, secondary extensions, internal opening, and associated abscesses before surgery. Clinical examination alone often underestimates the complexity of disease, particularly in recurrent and complex fistulas. Magnetic Resonance Imaging (MRI) has emerged as the imaging modality of choice because of its excellent soft tissue contrast and multiplanar capability. The aim is to evaluate the MRI classification of perianal fistula according to anatomical type and MRI grading system and to correlate these findings with intraoperative observations. Methods: A prospective observational study was conducted over 18 months at two surgical centers in West Bengal, India. Results: The study included 50 patients with a mean age of 48.44±12.45 years. Males constituted 56% of the study population. Intersphincteric fistulas were the most common anatomical type (54%), followed by transsphincteric (20%), suprasphincteric (18%), and extrasphincteric (8%). Grade I fistulas represented 46% of all cases. MRI accurately demonstrated the primary tract in all patients and showed excellent agreement with operative findings regarding fistula classification and anatomical extent. Conclusions: MRI provides accurate anatomical classification of perianal fistulas and correlates closely with operative findings. Routine preoperative MRI improves surgical planning, assists in identifying complex disease, and may reduce postoperative recurrence.