Fistula in ano: Endoanal sonography versus endoanal MR imaging in classification

PURPOSE: To assess agreement between endoanal sonography, endoanal magnetic resonance (MR) imaging, and surgery in depiction and classification of fistula in ano. MATERIALS AND METHODS: Twenty-eight consecutive patients with nonspecific, cryptoglandular fistula in ano were studied. The fistulas were classified with endoanal sonography, endoanal MR imaging, and surgery. Agreement between the modalities was also evaluated. RESULTS: Classification of fistulas was possible in 17 of 28 patients (61%) with sonography, in 25 of 28 (89%) with MR imaging, and in 26 of 28 (93%) with surgery. Concordance between endoanal sonography and MR imaging occurred in 46% of the cases (κ = 0.27, poor agreement); between sonography and surgery in 36% (κ = 0.09, no agreement); and between MR imaging and surgery in 64% (κ = 0.43, moderate agreement). CONCLUSION: Endoanal MR imaging more accurately allows depiction and classification of fistula in ano than endoanal sonography.