Preoperative local staging of rectal carcinoma with MR imaging and a rectal balloon.

Magnetic resonance (MR) imaging for the preoperative assessment of rectal carcinoma was evaluated. Thirty-three patients underwent MR imaging with a 1.5-T unit. On the basis of results of barium enema studies and/or digital examination, a balloon catheter was inserted to the level of the lesion before MR imaging. Both T1- and T2-weighted axial spin-echo images were obtained in all patients. With the balloon catheter, the three layers of the normal bowel wall could be seen on T2-weighted images. Muscular invasion was detected with a sensitivity of 90%, a specificity of 84%, a positive predictive value of 90%, a negative predictive value of 84%, and an overall accuracy of 88%. False-positive results were related to chemical shift artifact and intramural lymph node metastases. Perirectal fat invasion was detected with a sensitivity of 64%, a specificity of 89%, a positive predictive value of 82%, a negative predictive value of 77%, and an overall accuracy of 79%. One of the false-positive results was related to intramural lymph node metastases and the other to perirectal vessels. Evaluation of adjacent organ invasion was accurate in all patients. Lymph node metastasis was correctly detected in six of nine patients. Absence of lymph node metastasis was correctly predicted in 23 of 24 patients. Thus, MR imaging with a balloon catheter was useful for detection of tumor invasion into muscularis propria and adjacent organs; however, its demonstration of perirectal fat and lymph node involvement was less accurate.