Mesorectal lymph nodes: their location and distribution within the mesorectum

Total mesorectal excision is an alternative surgical approach for resectable rectal cancer and is associated with favorable results and a low rate of local recurrence. Despite the popularity of this technique, few data exist regarding the location and distribution of lymph nodes within the rectal mesentery. The purpose of this study was to define the distribution, size, and location of lymph nodes within the mesorectum and on the pelvic side wall.

Seven fresh cadavers at our institution's Fresh Tissue Dissection Laboratory were studied. The rectum, its mesentery, and all fatty tissue from both pelvic side walls were removed and placed in a lymph node clearing solution for 24 hours. After appropriate dissection, the distribution, size, and location of lymph nodes within the rectal mesentery and pelvic side wall tissue were documented.

A total of 174 lymph nodes were identified (approximately 25 per patient). The majority (>80 percent) of lymph nodes were smaller than 3 mm in diameter. Fifty-six percent of the nodes within the rectal mesentery were located in the posterior mesentery, and most were located in the upper two-thirds of the posterior rectal mesentery.

The majority of perirectal lymph nodes are small. There are few lymph nodes within the mesentery of the lower third of the rectum and relatively few in the right and left lateral portions of the mesorectum. We confirm that the majority of nodes are located in the proximal two-thirds of the posterior rectal mesentery. It is possible that removal of these nodes is responsible for the superior oncologic results found with total mesorectal excision in contrast to more traditional surgical techniques.