OBJECTIVETo evaluate high resolution MR in imaging of the anatomy and tumor invasion of the anal canal.

METHODSTwenty-three patients with low rectal cancer confirmed by pathology results were recruited as the study group and 20 patients without history of anal canal diseases were recruited as the control group. All patients received MRI examinations containing three TSE-T2WI sequences and three 3D-VIBE sequences. The distance between the tumor and the anal margin was measured in the study group. Two radiologists finished T staging of the tumor independently.

RESULTSMRI had a clear demonstration of the anatomy of the anal canal in all 20 control patients. The T staging of 23 patients of study group was T2 (n=8), T3 (n=7), and T4 (n=8), and the depth of anal canal invasion (T-DACI) was T0-DACI (n=10), T1-DACI (n=1), T2a-DACI (n=3), T2-DACI (n=3), T3-DACI (n=4) and T4-DACI (n=2). Eight patients received surgery and the consistency between pathological staging and imaging staging was 75%.

CONCLUSIONHigh resolution MRI has the capacity of demonstrating the complex anatomy of the anal canal, and can provide evidence of anal canal invasion for low rectal cancer.