Perianal fistula: volume MRI
Perianal pain and discharge.
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A high signal track extends superiorly from the left anal margin, just outside the sphincter complex. It penetrates the left lateral aspect of the sphincters and communicates with a horseshoe shaped posterior intersphincteric space collection. There is a track from the right side of this collection into the upper anal canal/low rectum at the 7 o'clock position. There is no deep pelvic or ischioanal fossa collection. The findings are of a trans-sphincteric fistula track with secondary branching and an intersphincteric space collection.
This case illustrates the value and utility of volume MRI for perianal fistula assessment. The volume sequences take 15 minutes to acquire, and can then be reformatted into the axial and coronal planes as the data is isotropic. The slice thickness is 0.6 mm. The contrast resolution is comparable to conventional T2 images. Very thin structures such as setons can be easily seen and followed within tracks.
The advantages are:
- reduced image acquisition time with its economic and patient comfort consequences
- isotropic data so can reconstruct in any plane
- contrast resolution comparable to conventional imaging