MRI For Evaluation Of The Anal Canal Anatomy And Diagnosis Of Anal Fistula At 3.0T

ObjectivesTo evaluate MRI for depicting the anal canal anatomy and diagnosis of anal fistula at 3.0T.Materials and Methods1.33 volunteers without any anorectal diseases and 15 cases with clinically suspected perianal fistula underwent MR imaging at 3.0T MR scanner(GE Signa Exciteâ…¡, Milwankee, Wisconsin, U.S.A.) with a 8-channel phased-array surface coil.2.MR pulse sequences included sagittal T₂ WI(SAG T₂ WI), coronal T₂WI(COR T₂WI), coronal T₂WI with fat suppression (COR T₂ FS), axial T₁WI(AX T₁WI),axial T₂WI(AX T₂WI), axial T₂WI with fat suppression(AX T₂ FS) and dynamic contrast enhanced magnetic resonance imaging (DCE).In order to display the anal canal exactly on the axial and coronal planes,we first obtain a sagittal T₂-weighted imaging,which reveals the extent and axis of the anal canal.Results1. The anatomic structure of the anal canal including the levator ani, muscle puborectalis,the external annal sphincter muscle was demonstrated distinctly.The upper portion of the anal canal comprised the internal sphincter muscle,the intersphincteric space and the muscle puborectalis.The lower portion of the anal canal comprised the internal sphincter muscle,the intersphincteric space and the external sphincter muscle.The more detailed anatomic structures were depicted at T₂ weighted imaging.2. 16 internal opening and 14 tracks were demonstrated in 15 cases.According to John Morris's study,3 cases were grade1,6 cases were grade2,3 cases were grade3,2 cases were grade4,1 cases were grade5 respectively, 2 cases with perianal abscess were noted. Though the internal opening was shown better at dynamic contrast-enhanced (DCE) imaging than at other sequences, there was no statistical difference between the DCE and Axial T₂ FS (P>0.05) . The fitula tracks were demonstrated much better at dynamic contrast-enhanced(DCE) imaging than at other sequences, there was statistical significance only between the DCE and Axial T₁ WI (P<0.05).Conclusion1.3.0T MR Imaging was a simple and feasible way to demonstrate the anorectaland pelvic floor structures.2. Optimized coronal T₂ fat suppression images and dynamic contrast-enhancedMR imaging were very helpful for the diagnosis and preoperative planning ofperianal fistula.