Fistula in ano: evaluation with low-field magnetic resonance imaging (0.1 T)

Patients suspected of having perianal suppurative disease often undergo a combination of several potentially painful, invasive procedures to establish or rule out the diagnosis. To evaluate the accuracy of low-field magnetic resonance imaging (MRI) in distinguishing patients with active anal fistulae and patients with no active fistulation we performed a retrospective study.

Fifty-six patients suspected of having anal fistulation were evaluated in the surgical outpatient clinic. Patients were examined with low-field MRI (0.1 T; gradient echo technique, TR/TE 1,500/40 and TR/TE 115/25, +/- gadodiamide (0.1 mM/kg intravenously)) in both coronal and axial planes, using a body quadrature coil. Altogether 71 MRIs were performed. In selected patients evaluation included endoanal ultrasonography, fistulography, and/or surgery. On the basis of the combined results of all available follow-up data for 6 months after the MRI, patients were placed in groups either having active fistulation or not.

MRI findings agreed with the combined findings of other examinations in 54 patients. Active or possibly active fistulae were found in 36 cases, whereas 33 patients showed no active fistulae. The kappa value is 0.944 (95% confidence limits, 0.866-1.021). In two patients the MRI findings disagreed with the combined findings of the other modalities.

The use of low-field MRI of the pelvic region in the investigation of suspected perianal fistulae is a feasible, reliable, and painless examination. MRI should be considered in patients with suspected complex anal fistulae. Future prospective studies are warranted.