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

Background: Patients suspected of having perianal suppurative disease often undergo a combination of several potentially painful, invasive procedures Ito establish or rule out the diagnosis. To evaluate the accuracy of low-fi eld magnetic resonance imaging (MRI) in distinguishing patients with active anal fistulae and patients with no active fistulation we performed a retro spective study. Methods: Fifty-six patients suspected of having anal fistul ation were evaluated in the surgical outpatient clinic. Patients were exami ned with low-field MRI (0.1 T; gradient echo technique, TR/TE 1500/40 and T R/TE 115/25, +/- gadodiamide (0.1 mM/kg intravenously)) in both coronal and axial planes, using a body quadrature coil. Altogether 71 MRIs were perfor med. In selected patients evaluation included endoanal ultrasonography, fis tulography, and/or surgery. On the basis of the combined results of all ava ilable follow-up data for 6 months after the MRI, patients were placed in g roups either having active fistulation or not. Results: 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 showe d no active fistulae. The kappa value is 0.944 (95% confidence limits, 0.86 6-1.021). In two patients the MRI findings disagreed with the combined find ings of the other modalities. Conclusion: The use of low-field MRI of the p elvic region in the investigation of suspected perianal fistulae is a feasi ble, reliable, and painless examination. MRI should be considered in patien ts with suspected complex anal fistulae. Future prospective studies are war ranted.