Ideal combination of MRI sequences for perianal fistula classification and the evaluation of additional findings for readers with varying levels of experience.

11 P erianal fistula is a common disease that most commonly originates from anal gland infections. Medical therapy has little treatment value, and patients eventually undergo surgery. The success of the surgery is closely associated with the preoperative evaluation (1). Therefore, it is of utmost importance to evaluate the course of the fistula and the presence of associated findings before surgical intervention because it can influence the surgical approach (2). Also, because recurrence is one of the most important problems following surgery, identification of the extensions of the disease with imaging methods aids in the surgical elimination of all sources of infection and ultimately decreases the percentage of recurrent disease (3). The preoperative evaluation of a fistula track by a surgeon includes inspection, palpation, probing, and the injection of colored dyes (2). The imaging methods employed to evaluate perianal fistulas are fistulography, computed tomography (CT), three dimensional (3D) endoanal ultrasonography (EAUS) (with or without the instillation of hydrogen peroxide into the track), and magnetic resonance imaging (MRI) with endoanal or pelvic coils or both. The description and classification of the primary track, the location of the internal opening (the radial site and the level), the presence of extensions (especially horseshoe extensions) and the presence of an abscess formation are the critical parameters for a complete evaluation of a fistula and should be implicated in the radiological reports. MRI is reported to be the most sensitive imaging method because it allows for the evaluation of secondary tracks and the detection of any possible extension to the supralevator fossa. Previous investigations performed to determine the role of MRI in this problem have indicated the value of the technique (2, 4–11). A concordance rate of 86%–88% between MRI and surgical findings was reported for the detection and classification of fistulas (12, 13). To the best of our knowledge, no previous reports have evaluated the value of each sequence for assessing the specific surgical parameters in addition to fistula classification. The purpose of our study was to assess the contribution of different MRI sequences in determining the perianal fistula type and in obtaining critical information for surgical decisions, as well as to define the optimal combination of sequences for readers with varying levels of experience.