MRI OF PERIANAL FISTULA: THE RELEVANT ANATOMY, IMAGING PROTOCOLS & SEQUENCES AND WHAT THE SURGEONS NEED TO KNOW
Rishi Philip Mathew*, Ammu Anne Mathew, Ram Shenoy Basti and Hadihally B. Suresh
Objective: To describe the relevant anatomy and MR imaging protocols and sequenes for assessing the perianal fistula and to identify the accuracy of MRI in evaluating the perianal fistula. Materials and Methods: This was a retrospective study involving 30 patients with clinically suspected perianal fistula referred for MR evaluation. All patients were examined on 1.5 T MRI (Philips Achieva 16 Ch.) scanner with external coiling. MR findings were then compared with the operative findings. Statistical analysis included percentage frequency, sensitivity and specificity. Results: The most common age group to be affected was the 4th decade (30%). Out of the total 30 patients, 28 (93%) were males and 2 (7%) were females. 23 patients had primary fistulas while 3 had undergone previous fistula surgery and presented with recurrence. 19 patients (73%) had intersphincteric fistula while 7 patients (27%) had transsphincteric fistula. 3 patients had perianal abscesses with no evidence of fistula. There was one false positive and one false negative case. As per our study MRI had a sensitivity and specificity of 96.15% and 75% respectively. Conclusion: MRI is an excellent tool for assessing perianal fistulae, in terms of it anatomy, extent of disease and it’s relation to the anal sphincters. MRI provides useful and accurate information for surgical planning, thereby decreasing the tendency for recurrence and also in avoiding complications such as fecal incontinence.
Keywords: Perianal fistulae, MRI, Intersphincteric, Transsphincteric, Suprasphincteric.
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