Finding the right tests…
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Emergency services available 24 x 7
Finding the right tests…
MRI
An MRI fistulogram maps the exact path of a fistula, an abnormal tunnel-like tract, most often around the anus, using MRI instead of the older X-ray fistulogram technique. It's especially useful for perianal fistulas linked to Crohn's disease or to an abscess near the anus, since these tracts can branch and hide extensions that are easy to miss on examination alone. One comparison found MRI far more accurate than conventional X-ray fistulography or CT at identifying the true path of these fistulas, largely because MRI shows soft tissue detail that X-ray-based methods can't capture. Unlike an X-ray fistulogram, MRI involves no radiation and doesn't require injecting contrast directly into the tract.
The scan maps the fistula's path, any branching tracts, and its relationship to the anal sphincter muscles. Your report describes the tract's complexity using a grading system, which your surgeon uses to plan treatment that avoids unnecessary damage to the muscles controlling continence.
An X-ray fistulogram involves injecting contrast dye directly into the fistula opening and taking X-ray images, which only shows the tract that takes up the dye and uses radiation. MRI instead uses the natural contrast between different tissue types, giving a panoramic view of the whole area, including hidden branches an X-ray-based method might miss entirely.
- Fistulas linked to Crohn's disease or an anal abscess often branch or have side tracts that aren't obvious from the outside - MRI shows how close a tract runs to the anal sphincter muscles, which control bowel continence - One study found MRI showed 100% accuracy in identifying Crohn's-related fistula tracts, compared with 0% for conventional X-ray fistulography and 11% for CT in the same comparison
Surgeons use MRI classification systems, such as the van Assche Index, to grade how complex a fistula is and to plan an approach that treats it while protecting the sphincter muscles as much as possible. Because these tracts can be more extensive than they appear on physical exam, this imaging step often changes the planned treatment before any procedure begins.
An X-ray fistulogram involves injecting dye into the tract and taking X-ray images, using radiation. An MRI fistulogram uses magnetic fields instead, giving a more complete view of the tract and its branches without radiation.
No, unlike the older X-ray method, MRI does not require injecting contrast dye directly into the tract to see it. The images come from the natural contrast between different tissue types instead.
These fistulas can branch or have hidden side tracts. MRI's soft tissue detail helps show the full extent of the tract, which studies have found more accurate than X-ray fistulography for this purpose.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Yes, that's one of the main reasons MRI is used. It helps your surgeon plan treatment that avoids unnecessary damage to the muscles that control continence.
No. It's a standard MRI exam using magnetic fields and radio waves, not X-rays.
Some protocols use an intravenous contrast injection to improve image detail, separate from any injection into the fistula tract itself. Ask your doctor or the centre what your specific scan involves.
Preparation can depend on the centre and your specific situation. Ask your doctor or the centre for guidance before your appointment.