A preliminary study of the draining lymph node basin in advanced lower rectal cancer using a radioactive tracer.

Purpose: This study was designed to examine the draining lymph node basin at highest risk of metastasis in lower rectal cancer using 99 mTc-tin colloid.

Methods: In 43 patients, the area with highest hot nodes density was defined as the draining lymph node basin using a gamma probe. Metastatic states of all removed lymph nodes were examined histologically.

Results: A total of 203 hot nodes were identified in 39 patients (91 percent) with a mean of 5.2 nodes. The number of removed lymph nodes was 808 nodes: 670 nodes in the mesorectum, and 138 nodes in the pelvis. In 21 patients, the metastatic states of 119 nodes were investigated histologically. From the distribution of the identified hot nodes, the draining lymph node basins were classified into two patterns: lateral type (n = 17), and mesorectal type (n = 22). Only 20 (17 percent) of 119 positive nodes were identified as hot node. Tumor cells that occupied the lymph node diffusely or massively probably interfered with the exact diagnosis of metastasis. Lymph node metastasis in the pelvis was observed in 5 patients (13 percent). One false negative was of the mesorectal type with diffuse metastases in the para-aortic lymph nodes. The remaining four patients were of the lateral type and all positive lymph nodes, including positive nonhot nodes, were located within the draining lymph node basin. Consequently, in 20 (95.2 percent) of 21 patients with lymph node metastasis, all positive lymph nodes were located within the draining lymph node basin of the tumor.

Conclusions: Two types of the draining lymph node basin of advanced lower rectal cancer were identified using this method. The concordance between lymph node metastases and the draining lymph node basin is good.