A Study on Lymph Node Distribution in the Main Lymph Node Area for Left-sided Colon Cancer.

Objectives: In advanced left-sided colorectal cancer, cutting the root of the inferior mesenteric artery (IMA) branching from the aorta is recommended for complete lymph node dissection. However, this procedure sometimes causes severe complications. This study aimed to elucidate the lymph nodes' distribution around the IMA and identify the most critical sites for lymph node dissection. Methods: This study included 30 consecutive patients with left-sided colorectal cancer who underwent curative resection with main lymph node dissection in a single institution between January and June of 2022. The mesenteric sections (main lymph nodes, IMA, left colic artery [LCA], and inferior mesenteric vein) were removed from the surgically excised specimen. Subsequently, whole-tissue sections were prepared and stained with hematoxylin and eosin. The positional relationships between each blood vessel and respective lymph nodes were then assessed using the pathological findings. Results: The main lymph nodes were identified in 26 out of 30 patients. The total number of dissected lymph nodes per patient was 0-30 (average: 5.3), and the median distance from the IMA to the main lymph node was 7.61 mm (1.87-43.26 mm). Dividing the lymph nodes into segments, we found 18%, 46%, and 36% of the lymph nodes in the proximal, middle, and distal segments, respectively. Additionally, all lymph nodes were found outside of the IMA sheath surrounding each arterial wall. Conclusions: In left-sided colorectal cancer, the main lymph nodes are mostly located around the LCA bifurcation, which may be essential to ensure main lymph node dissection for advanced stage cases.