Magnetic resonance imaging in the management of anal fistula and anorectal sepsis

Abstract

Complex perianal disease may be extremely debilitating for the patient with significant impingement on quality of life. The accurate identification of anatomical areas of involvement and subsequent appropriate management is crucial to achieving a successful outcome when treating anorectal sepsis and anal fistulae. Magnetic resonance imaging (MRI) has become a powerful tool in the evaluation of anal anatomy. In patients with complex disease MRI is an important adjunct in delineating disease location and extent, its relationship to sphincter muscles, and in planning management. MRI also plays an important role in evaluating the response to medical and surgical therapies.

Keywords: Crohn's disease; MRI; anal fistula; anorectal sepsis; anovaginal fistula.

Figure 1

Axial T2-weighted image at the level of the anal canal demonstrating mildly hyperintense internal sphincter (arrow), hypointense external sphincter (arrowhead), and levator ani muscle (L).

Figure 2

(A) Axial T2-weighted image at the level of the anal canal demonstrating a hyperintense translevator fistula (arrow). Also demonstrated are external sphincter (e), internal sphincter (i) and levator ani (L). (B) Axial short tau inversion recovery (STIR) image in the same patient showing a transsphincteric component (arrow). (C) Sagittal T1-weighted postcontrast image in the same patient demonstrates hyperenhancement along a contiguous fistulous tract to the skin (arrow).

Figure 3

(A) Coronal T2-weighted image demonstrating the low signal fibers portion of a fistulous tract extending to the perianal skin (arrow). (B) Coronal T1-weighted postcontrast image at the same level demonstrates hyperenhancement in the same region, representing inflammation.

Figure 4

(A) Axial T1-weighted postcontrast image demonstrating a small intersphincteric abscess (arrowhead). (B,C) Subsequent levels demonstrating a contiguous horseshoe-shaped fistula extending around the rectum (arrows).