[Ano-perineal fistula in MRI. Contribution of T2 weighted sequences].

INTRODUCTION

Anal fistulae are pathological conditions observed in infections of the Hermann and Defosses' glands or related to Crohn's diseases. The success and the lack of complication of surgical treatment depends on how accurately the tracks are assessed. The contribution of MRI in anal fistulas is now well established but the imaging appearance is not well discribed. The purpose of this work was to discribe the different patterns of lesions.

MATERIAL AND METHODS

Eighteen patients with anal fistulas were examined with MRI before operation (mean delay: 14 days. range: 1-56). SE T2 sequences, in coronal and axial planes referred to the anal canal were performed. The examinations were reviewed and compared with the results of surgical assessment to correlate imaging and surgical findings.

RESULTS

Lesions were hyperintense on T2-weighted sequences but were also iso- or poorly hyper-intense when they did not contain fluids but only inflammatory tissue. When involving the supra-levator space, lesions were nodular. They were well limited if they occurred in the supra-levator space itself. On the contrary, the rectal wall was thickened and hyper-intense when the fistulous tract reached it. Lesions were similar in Crohn's disease, except for anal fissures which were seen as a tubular hypersignal in contact with the anal lumen. On T2 sequences, healed fistulas were not visible.

CONCLUSION

The simple SE T2 sequences can discriminate between different patterns of lesions, especially for supra-levator extensions, fissures in Crohn's disease and chronic inflammatory lesions without fluid. The use of more recent machines or fat suppression sequences may improve the detectability of lesions, especially the more chronic ones.