Three-dimensional studies on the structure of the tissue surrounding the superior mesenteric artery.

The anatomy and topography of tissue surrounding the superior mesenteric artery were examined histopathologically, and the structure surrounding the superior mesenteric artery (SMA) was reconstructed with data from histologic examination and three-dimensional analyses. Specimens were obtained from three autopsy cases without abnormalities, two surgically resected cases of cancer of the pancreatic head, and one autopsy case of cancer of the pancreatic head. The endothelium or basal membrane of blood and lymph vessels were identified immunohistochemically, and the distribution of lymph nodes, blood vessels, lymph vessels, and collagen fibers was determined. The superior mesenteric plexus was found to be a relatively dense structure with a thickness of about 2 mm, composed of collagen fibers and connective tissue, which concentrically enveloped the small arteries, the superior mesenteric artery, nerve bundles, and capillaries. Lymph vessels larger than a few micrometers in diameter were often found outside of the plexus, and this plexus contained no lymph nodes in any sections. The three-dimensional study of the modes of spread along the superior mesenteric artery of pancreatic cancer revealed two types of spread: the tumor extends mainly by neural invasion, and the tumor extends mainly by lymph node metastases. These morphologic features suggest that lymphatic flow in the vicinity of the superior mesenteric artery passes primarily outside of the plexus, and complete excision of lymph nodes close to the superior mesenteric artery with preservation of the superior mesenteric plexus is feasible if there is no neural invasion into retropancreatic tissues.