Figure 4.

Grade 2 perianal fistula; intersphincteric fistula with an abscess. Fistulous tracks, inflammation and abscesses appear as areas of low to intermediate signal intensity and may not be distinguished from normal structures on T1-weighted images (A, arrow). Axial T2-weighted (B), axial (C) and coronal (E) fat-suppressed T2-weighted MR images show high-intensity fluid collection along the posterior wall of the anal canal (arrows). Axial (D) and coronal (F) contrast-enhanced fat-suppressed T1-weighted MR image shows an abscess which is peripherally enhanced (arrowheads) and contains a non-enhancing pus (D, arrow) in the intersphincteric space.