Role of MR Fistulogram in Preoperative Assessment of Anorectal Fistulas and Its Correlation with Intraoperative Findings

Abstract

Introduction: Perianal fistula is a common condition with significant morbidity pertaining to lower intestinal tract. Fistulas are usually classified surgically on the basis of types described by Park, which are of four types: (a) Intersphincteric (b) transsphincteric (c) suprasphincteric and (d) extrasphincteric. The various radiological methods of perianal fistula evaluation are X-ray fistulography, ultrasonography and MRI fistulogram. The aim of our study was to find out the incidence of different types of fistula and compare the imaging findings on MRI fistulogram with surgery.

Methods: 32 patients who underwent MR fistulogram were selected for the study. The following were assessed: type of fistula, position of internal opening, presence of secondary tracts & abscess and grading of fistula by St. James’s University Hospital MRI Classification, following which, the accuracy of MRI findings were correlated with intra operative findings.

Results: Among 32 patients with perianal fistulas, 25 (78.1%) were diagnosed as intersphincteric, 6 (18.7%) as transsphincteric and 1 (3.1%) as suprasphincteric fistulas on both MRI and surgical findings. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of MRI in detecting type of fistula and position of internal opening was 100%. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of MRI in detecting the number of internal openings was 95.65%, 90%, 95.65%, 90% and 93.93%. Similarly, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy of MRI in detecting abscess was 81.81%, 92%, 81.81%, 92% and 88.88%. For detecting secondary tracts, sensitivity, specificity, positive predictive value, negative predictive value and accuracy of MRI was 90.9%, 95.65%, 90.9%, 95.65% and 94.11% respectively.

Conclusion: MR fistulogram was found to be a valuable modality of imaging in pre-surgical evaluation of perianal fistulas.