Figure 25. Transsphincteric perianal fistula. Coronal dynamic contrast-enhanced gradient-echo MR image obtained with fat suppression in 34-year-old man without a history of Crohn disease shows a left-sided fistula (arrow) that pierces both sphincteric layers to exit the middle third of the anus. The fistula tracks inferiorly within the ischiorectal fossa. Note conspicuity of high-signal-intensity lesion due to inflammatory enhancement. (Case courtesy of John A. Spencer, MD, Leeds, England.)