Magnetic Resonance Imaging Patterns of Complex Anal Fistula: A Case Series- MRI of complex anal fistula

Abstract

Complex anal fistula requires accurate preoperative mapping because unrecognized secondary tracts, supralevator extension, and abscesses increase the risk of persistent sepsis and recurrence. Magnetic resonance imaging (MRI) is central to defining fistula anatomy and guiding surgical planning. Case presentation: We describe four male patients aged 17-46 years who presented with persistent or recurrent perianal discharge. Pelvic MRI demonstrated transsphincteric fistulas in all cases. The imaging spectrum included multiple internal openings, bilateral external openings, branching secondary tracts, extension to the levator ani, pelvic sidewall or periprostatic region, circumferential perirectal inflammatory collections, perineal abscess close to the corpus spongiosum, gas-containing fistulous tracts, and horseshoe abscess involving the intersphincteric and supralevator spaces. MRI consistently depicted low signal intensity on T1-weighted images, high signal intensity on T2-weighted and fat-suppressed T2-weighted images, and marked rim or wall enhancement after gadolinium administration. Surgical management was individualized and included abscess drainage, excision of fibrotic fistula tracts, seton placement, and laser fistula treatment. Conclusion: This case series highlights the wide anatomical variability of complex anal fistulas and the practical value of MRI in demonstrating occult branches and abscesses. Structured MRI reporting using clock-face location, relationship to sphincters and levator ani, internal and external openings, and associated collections can improve communication between radiologists and surgeons.