Preoperative MRI of rectal cancer with and without rectal water filling: An intraindividual comparison

OBJECTIVE. The purpose of our study was to determine if a rectal distention using warm water may improve the accuracy of MRI for the preoperative staging of rectal carcinoma. SUBJECTS AND METHODS. Sixty-two patients with surgically proven rectal carcinomas underwent pelvic MRI before and after a rectal distention by warm water. Four radiologists, who were blinded to the study, reviewed each set of T1- and T2-weighted axial images obtained before and after the rectal distention and scored the image of the tumor. The accuracies for determining the tumor penetration of the outer wall of the rectum and the regional lymph node involvement were compared by analyzing the area under the receiver operating characteristic curve (A _z). RESULTS. For all reviewers, the tumor depiction scores were significantly higher in the distended images (3.8-3.9 for reviewers 1-4) than in the nondistended images (3.0-3.2) (p < 0.01). For determining the outer wall penetration, the accuracy of the three reviewers was significantly higher with the rectal distention images than with the nondistended images (p < 0.05). The mean accuracy of the all reviewers was significantly better with the distended images (Az = 0.922) than with the nondistended images (Az = 0.841) (p < 0.05). For determining the presence of regional lymph node involvement, all the reviewers came to similar conclusions in analyzing the two image sets. CONCLUSION. Rectal distention by water filling may improve the depiction of a primary rectal tumor and the assessment accuracy of a perirectal tumor extension, but it does not improve the accuracy for determining the presence of regional lymph node involvement.