High-resolution MRI of the anatomy important in total mesorectal excision of the rectum.

OBJECTIVE: The surgical removal of a rectal carcinoma and the adjacent lymph nodes in an en bloc package lessens the risk of local recurrence due to residual tumor. Heightened awareness of good surgical techniques has created much interest in the anatomy involved in total mesorectal excision surgery, with particular focus on the fascial planes and nerve plexuses and their relationship to the surgical planes of excision. Clear preoperative depiction of these relationships is of value in determining tumor resectability. The aim of this study was to describe the radiologic appearance of these anatomic structures. SUBJECTS AND METHODS. High-spatial-resolution T2-weighted MRI was performed using a 1.5-T system in cadaveric sections and in patients before they underwent total mesorectal excision surgery. Anatomic dissections of sagitally sectioned hemipelves were compared with MRIs obtained in vivo to establish criteria for visualization of the structures relevant to anterior resection of the rectum. RESULTS: High-spatial-resolution MRI depicted a number of structures of importance in total mesorectal excision surgery. The mesorectal fascia, which forms the boundary of the surgical excision plane in total mesorectal excision, was identified, and the presacral fascia, peritoneal reflection, and Denonvilliers' fascia were also shown. Structures 1-2 mm in diameter were visualized because the contrast resolution afforded by T2-weighted fast spin-echo imaging permitted depiction of the inferior hypogastric nerve plexus and the fascial planes within the posterior pelvis. CONCLUSION: Anatomic landmarks important to the performance of rectal cancer surgery, in particular the mesorectal fascia, may be defined on MRI and are of potential importance in the staging of tumors, assessing resectability, planning surgery, and selecting patients for preoperative neoadjuvant therapy.

Morphologic predictors of lymph node status in rectal cancer with use of high-spatial-resolution MR imaging with histopathologic comparison.

PURPOSE: To evaluate signal intensity and border characteristics of lymph nodes at high-spatial-resolution magnetic resonance (MR) imaging in patients with rectal cancer and to compare these findings with size in prediction of nodal status. MATERIALS AND METHODS: Forty-two patients who underwent total mesorectal excision of the rectum to determine if they had rectal carcinoma were studied with preoperative thin-section MR imaging. Lymph nodes were harvested from 42 transversely sectioned surgical specimens. The slice of each lymph node was carefully matched with its location on the corresponding MR images. Nodal size, border contour, and signal intensity on MR images were characterized and related to histologic involvement with metastases. Differences in sensitivity and specificity with border or signal intensity were calculated with CIs by using method 10 of Newcombe. RESULTS: Of the 437 nodes harvested, 102 were too small (<3 mm) to be depicted on MR images, and only two of these contained metastases. In 15 (68%) of 22 patients with nodal metastases, the size of normal or reactive nodes was equal to or greater than that of positive nodes in the same specimen. Fifty-one nodes were above the area imaged, and seven of these contained metastases. The diameter of benign and malignant nodes was similar; therefore, size was a poor predictor of nodal status. If a node was defined as suspicious because of an irregular border or mixed signal intensity, a superior accuracy was obtained and resulted in a sensitivity of 51 (85%) of 60 (95% CI: 74%, 92%) and a specificity of 216 (97%) of 221 (95% CI: 95%, 99%). CONCLUSION: Prediction of nodal involvement in rectal cancer with MR imaging is improved by using the border contour and signal intensity characteristics of lymph nodes instead of size criteria.