Mesorectal and lateral node metastasis and micrometastasis in lower rectal cancer

To study lymph node metastasis and micrometastasis within the mesorectum and lateral pelvic area in lower rectal cancer.

Specimens of 96 patients, who underwent total mesorectal excision (TME) and lateral lymph node dissection (LLND), were included.

An average of 19.4 mesorectal lymph nodes were examined. Horizontally, more than 30 percent of involved lymph nodes were located in the outer layer of the mesorectum. Longitudinally, metastasized lymph nodes were harvested from the distal, paratumoral and proximal mesorectum of 6, 42 and 29 specimens, respectively. Fourteen specimens were observed to have circumferential resection margin involvement, while another 3 had micrometastasis. The average amount of harvested lateral pelvic lymph nodes was 12.1. Most (1052/1159) of the lateral nodes were defined as negative. Fourteen and 11 specimens were examined to contain lateral node metastasis and micrometastasis, respectively. Among regions of the lateral pelvic area, middle rectal root (44%), internal iliac (28%) and obturator (20%) were more likely to be involved by cancer spread.

Complete excision of the mesorectum is essential for local clearance of lower rectal cancer. Mesorectal margin involvement and lateral metastasis underlined the limitation of single surgical procedure, thus suggesting the significance of neoadjuvant therapy.