[Optimal lymph node dissection for colorectal cancer]

Previous studies on the distribution of positive lymph nodes have revealed that the colon should be resected 10 cm from the tumor on both sides and that the intermediate nodes along the main vessel should be dissected in patients with colon cancer. In rectal cancer, superior lymphatic spread along the inferior mesenteric artery (IMA) is the main metastatic route. The IMA should be dissected immediately after the bifurcation of the left colic artery, and the intermediate lymph nodes should be removed. The positive rate of the lateral lymph nodes is about 10%. The rate of local failure is high and the prognosis is poor in patients with positive lateral lymph nodes, even if the lateral lymph nodes have been dissected. However, it has been reported that lateral lymph node dissection combined with excision of the internal iliac vessels results in good disease-free survival in patients with positive lateral nodes. Therefore the indications for lateral node dissection remain controversial. Lymphatic spread into the mesorectum on the anal side has been shown to be an important factor in local failure. The mesorectum should be resected for up to 4 or 5 cm from the inferior tumor margin in middle rectal cancer, and the entire mesorectum should be removed in lower rectal cancer. Nerve tissue preserved in pelvic autonomic nerve-preserving surgery contains a small amount of lymphoid tissue and lymph nodes. Therefore the extent of lymph node dissection and the area of autonomic nerves to be preserved based on tumor site or tumor penetration remain controversial.