Rectal Cancer: A Compartmental Disease. The Mesorectum and Mesorectal Lymph Nodes

Abstract

Even though the technique of total mesorectal excision has been widely used, there have been few detailed descriptions of the distribution of lymph nodes within the rectal mesentery. We describe the results of our anatomic study of lymph node size and distribution within the mesorectum and pelvic side-wall tissue using a fat-clearing solvent in seven male cadavers, and we used a similar technique to examine the mesorectum in a patient who underwent total mesorectal excision after preoperative chemoradiation for a uT3 rectal cancer. In both the cadavers and our patient, the majority of lymph nodes were located within the posterior upper two-thirds of the mesorectum. Few lymph nodes were located in the distal mesorectum or anteriorly. In the cadavers, the majority of lymph nodes were less than 3 mm in diameter. In the patient who had received preoperative chemoradiation, routine tissue processing yielded only four lymph nodes, whereas processing in fat-clearing solvent yielded 25 additional nodes. The majority of these nodes, in contrast to those observed in cadavers, were less than 1 mm in diameter. The majority of mesorectal lymph nodes were located within the upper two-thirds of the posterior mesorectum. Complete removal of nodes in this area may, in part, explain the superior results of total mesorectal excision with respect to local recurrence.