This composite figure illustrates a human intersphincteric perianal fistula using two imaging modalities. Image (a) is a conventional radiographic fistulogram showing a thin, contrast-filled tract near the midline with an internal communication point within the anal canal. Images (b), (c), and (d) are sequential posterior-to-anterior coronal fat-saturated T2-weighted MRI scans. These images demonstrate the anatomy of the anal sphincter complex where the external anal sphincter appears as a hypointense (dark) lateral structure and the internal sphincter/mucosa is relatively hyperintense. A small, high-signal intensity (bright) tract is clearly visible within the intersphincteric plane, located medially to the right external sphincter. The sequence captures the fistula's course as it originates in the intersphincteric space and eventually opens into the anal canal (arrow in d). The fat-saturated MRI technique provides excellent contrast between the fluid-filled inflammatory tract and the surrounding muscular structures and suppressed ischioanal fossa fat, which is essential for accurate surgical planning and classification of perianal fistulous disease.

This diagnostic image is an axial MRI scan of the male pelvis, specifically a dedicated fistula protocol study with intravenous contrast. The image highlights the perianal region and pelvic floor anatomy. Anatomical landmarks include the gluteal muscles, pelvic bones, and the anal canal. Red arrows indicate bilateral, hyperintense linear tracts representing intersphincteric perianal fistulas. These tracts are situated within the intersphincteric space between the internal and external anal sphincters, with internal openings visualized at approximately the 5 o'clock and 7 o'clock positions. The rectum and sigmoid colon show evidence of mild circumferential wall thickening, suggesting an underlying inflammatory process. The surrounding soft tissues show subtle signal changes consistent with inflammation but lack evidence of complex trans-sphincteric extension, supralevator involvement, or localized abscess formation. This imaging is clinically significant for the classification of perianal Crohn's disease or chronic inflammatory conditions like Schistosomiasis-related granulomatous colitis, facilitating surgical planning and disease staging.

This composite educational image demonstrates the radiological assessment of perianal anatomy and fistula measurement using MRI. Panel A shows an unlabeled coronal T2-weighted MRI sequence of the perianal region. Panel B provides a color-coded anatomical overlay on the same MRI: the fistula tract is highlighted in green, the internal anal sphincter in yellow, the external anal sphincter (EAS) in red, the puborectal muscle in purple, and the levator ani in orange. The bottom schematic diagram (Panels C and D) illustrates the methodology for quantitative measurement. Label C indicates the vertical length or height of the external anal sphincter, while Label D represents the level of fistula penetration, defined as the vertical distance to the most cranial aspect of the tract penetrating the EAS or puborectal muscle. This resource is designed for radiologists and colorectal surgeons to standardize the classification and reporting of complex perianal fistulas.