Endoanal magnetic resonance imaging.

PURPOSE

To review the results of endoanal magnetic resonance imaging (MR) in patients with anal sphincter defects and anal fistulas.

MATERIAL AND METHODS

Normal volunteers, patients with faecal incontinence, and patients with perianal fistulas were studied. Endoanal MRI was performed with a rigid, endoluminal anal coli with a diameter of 19 mm. An axial T2-weighted gradient echo and sagittal, coronal and radial T2-weighted turbo spin-echo sequence were performed.

RESULTS

Normal anatomy. The most important finding was that the outer part of the anal sphincter complex is caudally the external sphincter, while the upper part is the puborectal muscle. This is in contrast to previous anatomical and surgical studies. Our findings concerning the internal sphincter and longitudinal muscle are not very different from previous studies. The internal sphincter is the inner part of the anal sphincter, surrounded by the intersphincteric space with the longitudinal layer. SPHINCTER DEFECTS: Especially the external sphincter is more clearly and consistently demonstrated with MRI than with endoanal sonography. In our experience so far, the results of endoanal sonography and MRI are approximately comparable for internal sphincter defects, but MRI is superior in the detection of external sphincter defects. PERIANAL FISTULAS: Our results of a study of endoanal sonography and endoanal MRI in perianal fistulas indicate preference for MRI especially in the classification of transsphincteric fistulas. The accurate identification of the external sphincter and the differentiation between scar tissue and a track with endoanal MRI are the major reasons for this preference. In another study was demonstrated that endoanal MRI was preferable to surface coil MRI.

CONCLUSION

The introduction of endoanal MRI has been a major step in anal imaging. The multiplanar capacities and high inherent contrast facilitate the demonstration of the anal anatomy. Our preliminary results indicate superiority of endoanal MRI as compared to endoanal sonography, especially in the identification of external sphincter defects and the classification of perianal fistulas.