Preoperative MRI of perianal fistula: Is it really indispensable? Can it be deceptive?

Objective: The study aims not only to determine the value of preoperative MRI of perianal fistula but also to detect MRI fallacious results, if any. Also, it aims to suggest how we can limit such false positive MRI results that may lead to unnecessary surgery. Patients and methods: This was a prospective comparative study, included 100 patients. Fifty of them (group A) were operated following the guidance of preoperative MRI, while the other 50 patients (group B) directly operated without MRI. The study protocol was approved by the ethics committee in Al-Mana General Hospital. Results: Group A: surgically proven 24 patients grade 1, 13 grade 2, 4 grade 3, 4 grade 4 and 3 grade 5. MRI grading was 26 grades I, 13 grade 2, 4 grade 3, 4 grade 4 and 3 grade 5. Two patients were false positive. Postoperative complications: 2 recurrences, 1 incontinence and 1 both recurrence and incontinence. Group B: surgically proven 22 patients grade 1, 11 Grade 2, 8 grade 3, 3 grade 4 and 3 grade 5. Clinical preoperative grading was 42 patients grade 1 and 8 grade 2. Three patients were false positive. Postoperative complications: 17 recurrence, 6 incontinence, 3 concomitant recurrence and incontinence. Conclusion: MRI is a very helpful tool of preoperative imaging of perianal fistula. Its fallacious preoperative positive results – that may lead to unnecessary surgeries – can be corrected by standardizing IV gadolinium contrast as routine protocols or using complementary Color Doppler US examination of the fistulous track.