Figure 3b. Transsphincteric fistula. (a, b) Sagittal T2-weighted two-dimensional turbo SE (3,427/150) MR images show a hyperintense fistula track (white arrowhead) posterior to the anal canal (black arrowhead). The track crosses the sphincter muscles (white arrow in a) posteriorly. (c, d) Transverse T2-weighted two-dimensional turbo SE (3,427/150) MR images show the track (black arrow in c) first coursing laterodorsally from the left external sphincter muscles (arrowhead in c), then crossing the external sphincter at a midanal level (black arrow in d). A transsphincteric fistula track was diagnosed at MR imaging and confirmed at surgery. The internal opening was correctly predicted as being at the five o’clock position dorsally, at midanal level (white arrow in d). Note that the internal opening is not directly visualized but can be inferred only from the course and proximity of the fistula track in the sphincter muscle compartments. The arrowhead in d indicates the internal sphincter muscle.