Endoluminal MR imaging of the rectum and anus: Technique, applications, and pitfalls

Anorectal diseases (eg, fecal incontinence, perianal and anovaginal fistula s, anorectal tumors) require imaging for proper case management. Endolumina l magnetic resonance (MR) imaging has become an important part of diagnosti c work-up in such cases, Optimal endoluminal MR imaging requires careful at tention to patient preparation, imaging protocols, and potential pitfalls i n interpretation. Comfortable positioning and the use of an antiperistaltic drug are vital for adequate patient preparation. Selected sequences and im aging planes are used in imaging protocols tailored for specific diseases. In fecal incontinence, three-dimensional sequences allow detailed demonstra tion of the anal anatomy and related defects, In perianal and anovaginal fi stulas, longitudinal imaging planes help determine the superior extent of t he abnormality, In anorectal tumors, T1-weighted turbo spin-echo MR imaging can help detect extension into the perirectal fat and T2-weighted turbo sp in-echo MR imaging is used to optimize contrast between tumor and the recta l wall. Off-axis and radial imaging planes are used in all anorectal diseas es to minimize partial volume effects, Potential pitfalls include various p arts of the normal anal anatomy mimicking sphincter defects, veins and hemo rrhoids mimicking fistulas and abscesses, and overhanging tumor mimicking m ore extensive tumor. Adequate patient preparation combined with proper tech nique and a knowledge of potential pitfalls will allow optimal endoluminal MR imaging of the rectum and anus.