E2076. MRI Fistulography: An Essential Pre-Operative Navigating Tool for a Safer Surgery
Medical College Badora
Medical College Badora
Recurrence of perianal fistula is a common complication of any surgery for perianal fistula. Etiology is usually an infection or secondary tract extension that have escaped surgical detection and thus gone untreated. Fistulography is the most traditional modality to define the fistula anatomy; however, it is unreliable and difficult to interpret. Although the sphincter mechanism and intersphincteric plane are usually well visualized with endosonography, the external sphincter can be difficult to assess in some individuals. With multiplanar capabilities and high contrast resolution, MRI shows the surgical anatomy accurately and identifies complex fistulas and secondary fistulous tracts with greater surgical concordance. This study was undertaken to evaluate role of MRI in determining the relationship of fistula tract to the sphincter complex and detection of any associated abscesses or secondary tracts.
Educational Goals / Teaching Points
This exhibit aims to evaluate the role of MRI in determining the relationship of any fistulous tract to sphincter complex-associated abscesses or secondary tracts and to classify fistula according to St. James Hospital and University classification by postoperative confirmation.
Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
This is a cross-sectional, record-based study of 70 patients with perianal fistula. The study was approved by the scientific and ethical committee of the institution. Written informed consent was taken from each patient prior to conducting the scan. The MRI studies were conducted on 1.5 Tesla with phased-array body coil, oblique transverse and coronal planes, perpendicular and parallel to the anal sphincter, and were planned with the help of a midline sagittal sequence. Out of 70 patients, 63 were found to have fistula and seven patients were found to have sinus tracts on MRI. The most common age group was 41–50 y (28.57%). According to St James classification, the most common type of fistula was grade III (transphincteric) (36.50%). Other common types with descending order of frequency included grade-I (intersphincteric) (34.93%), grade IV (transphincteric fistula with an abscess) (15.87%), grade II (simple intersphincteric fistula with an abscess or collection) (6.34%), and grade V supralevator fistula (6.34%). The most common location for internal opening was posteriorly at 6 o’clock (44.44%) Out of seven cases of sinus tracts diagnosed on MRI, actual presence of sinus tracts was found in five cases and two turned out to be fistulous tracts. Out of 21 cases with secondary tracts on MRI, 19 patients were confirmed to have secondary tracts intraoperatively, leading to a sensitivity of 96% and specificity of 83% (p < 0.0001).
MRI with its multiplanar capabilities and high spatial and contrast resolution has excellent accuracy for demonstrating the anal sphincter anatomy and the fistulous tracts, their extensions, and their associated complications. Thus, when used as a preoperative tool, it may reduce the chances of recurrence or injury to sphincters. Larger multicenter studies would be beneficial for generalized extrapolation.