MAGNETIC-RESONANCE-IMAGING OF FISTULA-IN-ANO - STIR OR SPIR

Patients with clinically suspected anorectal sepsis were studied using MRI in order to determine if T-2 weighted sequences with fat suppress ion conveyed any additional benefit over conventional short tau invers ion recovery (STIR) sequences. 23 consecutive patients (16 male) under going MRI for suspected perianal sepsis were studied prospectively usi ng a 1.0 T whole body system and body coil. Axial and coronal T-1 weig hted turbo spin echo sequences were obtained, followed by STIR and T-2 weighted spectral fat saturation inversion recovery (SPIR) sequences. Images were assessed for the presence of sepsis or fistula, and infor mation provided by the sequences compared. Active disease was diagnose d in 17 patients, 14 of whom had fistula-in-ano; one intersphincteric, 10 transsphincteric and three extrasphincteric. Internal openings wer e identified in all of these 14 patients; anal in 10, rectal in two, a nd both in two. Diagnosis and fistula classification was possible in a ll of these 14 subjects on the basis of STIR sequences alone. The anal sphincters and pelvic floor musculature were better resolved by STIR than SPIR, leading to easier and more confident determination of fistu la anatomy in eight of the 14 (57%). In no case did STIR sequences fai l to resolve inflammation seen subsequently on SPIR, despite reduced t rack intensity. T-1 weighted sequences were generally non-contributory . Both STIR and SPIR sequences are adequate to classify fistula-in-ano , but classification was easier with STIR due to superior resolution o f pelvic floor structures.