MR imaging and computed tomography in patients with rectal tumours clinically judged as locally advanced

To compare magnetic resonance (MR) imaging and computed tomography (CT) in the local staging of locally advanced rectal tumours.

Sixteen consecutive patients who, after pre-operative radio-chemotherapy (RCT), had surgery for rectal tumours clinically judged as extending into neighbouring tissues in the pelvis, were examined using MR and CT before and after treatment. The examinations were reviewed by four radiologists. The relation of the tumours to 14 different anatomic structures in the pelvis in a total of 50 examinations was studied. The results were compared to surgical and histopathological findings.

Seven patients had tumour infiltration of adjacent organs in the pelvis at surgery, the most common being the urinary bladder, prostate, uterus and small bowel. MR predicted involvement of the urinary bladder and the uterus better than CT. However, there were more false positive findings on MR than on CT compared to surgical and histopathological findings.

For staging of advanced rectal cancers, the overall results were not significantly better for MR than CT. If involvement of the urinary bladder and the uterus cannot be ruled out using CT, MR is advocated due to its higher soft tissue contrast resolution and multi-planar capability.