Comparison of Preoperative and Postoperative MRI After Fistula-in-Ano Surgery: Lessons Learnt from An Audit of 1323 MRI At a Single Centre

A total of 1323 MRI were done in 1003 fistula-in-ano patients, out of which 702 patients underwent surgery. In 702 patients, there were 361 recurrent fistulas, 153 had associated abscess, 388 had multiple tracts, 146 had horseshoe tract, and 76 had supralevator fistula. In total, 320 postoperative MRI scans were done in 180/702 patients. The requirement of postoperative MRI was significantly higher in complex (grades III–V) than simple fistulas (grades I–II) [43.5% (136/313) vs. 11.3% (44/389), respectively, P < 0.0001]. In early postoperative period (8 weeks), healing (granulation) tissue was difficult to differentiate from active fistula tract/pus. The complete radiological healing took at least 10–12 weeks. So getting MRI scan for the assessment of healing was more accurate after 12 weeks. MRI was very accurate to identify postoperative complications like abscess, missed tract or non-healing of a tract. MRI detected such complications even in apparently clinically healed tracts. Closure/healing of internal opening and intersphincteric tract was assessed accurately by MRI and correlated well with the fistula healing.