Fistula-in-ano Presenting as Scrotal Swelling: Magnetic Resonance Imaging Demonstration of Penile and Scrotal Extension with Pericorpus Spongiosum Abscess

Abstract Fistula-in-ano rarely extends anteriorly into the penile shaft and scrotal structures, and when it does, the anorectal origin of disease may not be clinically apparent, particularly in patients presenting predominantly with scrotal swelling. We report a 27-year-old male who had a 6-month history of perianal pain radiating to the perineum and scrotum, along with a gradually increasing left scrotal swelling. The patient was referred to us for magnetic resonance imaging (MRI) fistulography, which revealed an internal opening at the 1 o’clock position abutting the external anal sphincter, with a continuous fistulous tract extending anteriorly through the left obturator internus region, then along the inferolateral corpus spongiosum for approximately 66 mm, reaching the penoscrotal junction and scrotal base. A well-defined pericorpus spongiosum abscess measuring 11 mm × 8 mm × 13 mm (craniocaudal × anteroposterior × transverse) in the penile shaft showed diffusion restriction on diffusion-weighted imaging, confirming purulent content. The case illustrates how MRI fistulography, through systematic multiplanar tract mapping and diffusion-weighted imaging, enables accurate delineation of complex fistulous tract extension and characterization of associated collections, preventing dangerous underestimation of disease extent in atypically presenting perianal fistulas.