Objective: To provide the mode of cancer distribution in the mesorectum and circumferential resection margin.
Methods: Large slice technique was used in the pathologic study of 62 specimens operated on following the principles of total mesorectal excision (TME).
Results: More than 40% of all the observed neoplastic foci were located in the outer layer of the mesorectum in Stage III patients. Further analysis of the foci's localities with respect to the primary tumor's locality showed that ipsolateral neoplastic foci (44.44%) were significantly more than the contralateral neoplastic foci (13.33%) in the mesorectum (P<0.05). Extramural distal spread was found in 8 cases with the maximum extent of 3.5 cm. No significant difference in occurrence of circumferential margin involvement (CMI) was observed among tumors of different location, but tumors of poorer differentiation were noted to have a higher risk of CMI.
Conclusion: Large slice technique offers a whole image of rectum, mesorectum, together with the position of neoplastic foci. There are outer preponderance and lateral discrepancy of neoplastic foci distribution in the mesorectum. A distal clearance margin of 4 cm would be mandatory. We advocate the adoption of TME as the baisc surgical principles in treating patients with rectal cancer and in avoiding surgery-related circumferential margin involvement.