Preoperative Assessment by MR Fistulogram in Patients with Perianal Fistula and Its Correlation with Operative Findings and Postoperative Outcome

Author(s): Annapurna Patwari1 , Nihar Ranjan Sarkar2 , Makhan Lal Saha3

BACKGROUND Inflammatory bowel disease causing inflammation, perianal abscess, or any situations like carcinoma or injury of anorectal region can produce fistulisation of anal area. A major advancement in imaging evaluation has been done by magnetic resonance imaging which can be a gold standard for perianal fistula. Magnetic resonance imaging has magnificent soft tissue delineation ability. It can take images in multiple planes. It can be operator independent with better field of view (FOV). METHODS As a standard imaging approach at our institution (3T MRI machine) we used a T2 weighted (T2W) and T2FS sequences. As we know, the anal canal is tilted forward. We use a T2 weighted (T2W) single shot image in sagittal plane with midline coursing through the anal canal; then we defined the FOV and scan extent and take coronal and axial images particularly taking the point of view of the position of long axis of the anal canal. We include the whole of perineum and levator ani muscles for evaluation of the extent of disease into inferiorly to the gluteal folds and superiorly upwards above the levator ani muscles. Frequency selective fat suppressed T2 weighted (T2W) sequence gives good spatial resolution. It helps in better understanding of anatomy and pathology of tracks and fluid collections along the fistula which become hyper intense in T2W image. RESULTS In this study, 50 patients were included of which 38 were males and 12 were females. 76 % were males and 24 % were females. In this study, perianal fistulas were classified as intersphincteric, transsphincteric and suprasphincteric. Out of 50 patients, 30 patients (60 %) had intersphincteric fistulas, 17 patients (34 %) had transsphincteric fistulas and 3 patients (6 %) had suprasphincteric fistulas. In this study, MR findings were correlated with OT findings. Out of 50 patients, 45 (90 %) patients had matched findings and 5 (10 %) patients had non-matched findings. The p-value is < 0.0001, which is significant. CONCLUSIONS MR Fistulogram has become the recommended diagnostic method as it can depict perianal fistulas in soft tissues wonderfully. It shows the position of the fistula in anal region, especially in connection to sphincters of perianal area, and identifies internal and external orifices and branching of the fistula.