3-DIMENSIONAL STUDIES ON THE STRUCTURE OF THE TISSUE SURROUNDING THE SUPERIOR MESENTERIC-ARTERY

The anatomy and topography of tissue surrounding the superior mesenter ic artery were examined histopathologically, and the structure surroun ding 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 surg ically resected cases of cancer of the pancreatic head, and one autops y case of cancer of the pancreatic head. The endothelium or basal memb rane of blood and lymph vessels were identified immunohistochemically, and the distribution of lymph nodes, blood vessels, lymph vessels, an d collagen fibers was determined. The superior mesenteric plexus was f ound to be a relatively dense structure with a thickness of about 2 mm , composed of collagen fibers and connective tissue, which concentrica lly enveloped the small arteries, the superior mesenteric artery, nerv e bundles, and capillaries. Lymph vessels larger than a few micrometer s 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 pancrea tic cancer revealed two types of spread: the tumor extends mainly by n eural invasion, and the tumor extends mainly by lymph node metastases. These morphologic features suggest that lymphatic flow in the vicinit y of the superior mesenteric artery passes primarily outside of the pl exus, and complete excision of lymph nodes close to the superior mesen teric artery with preservation of the superior mesenteric plexus is fe asible if there is no neural invasion into retropancreatic tissues.