Assessment by MR imaging of local staging of rectal cancer

This study was designed to assess the value of MRI in patients with rectal carcinoma. Thirty-one patients were preoperatively evaluated with MR imaging using a 1.5 T unit. Based on the results of a barium study, and/or digital examination, a balloon catheter was inserted to the level of the lesion before examination. Both T1- and T2-weighted transaxial images were obtained in all patients. By using a balloon catheter, three layers of the normal bowel wall were seen on T2-weighted images. Detection of muscular invasion was true positive (TP) in 15 patients, true negative (TN) in 8, false positive (FP) in 1 and false negative (FN) in 1. The FP and FN results were related to chemical shift artifact (CSA). Detection of invasion of perirectal fat was TP in 7, TN in 13, FP in 2, and FN in 3. Two of the FP results were also related to CSA and 1 was related to intraluminal lymph node enlargement. It was impossible to detect fat invasion macroscopically in the FN patients. MR imaging was useful for local staging of rectal carcinoma. Using the balloon catheter provided more reliable bowel distinction than only air insufflation. (author)