Lymph and blood capillaries of the human gastric mucosa. A morphologic basis for metastasis in early gastric carcinoma.

The distribution of lymph and blood capillaries has been studied by light and transmission electron microscopy in 16 endoscopic and surgical specimens of human gastric mucosa and submucosa. Four specimens were completely normal, seven showed mild gastritis, and five showed severe gastritis. On light microscopy, no definite distinction could be made between small mucosal lymph and blood capillaries. The distinction was achieved only by transmission electron microscopy where lymph capillaries could be identified by the presence of anchoring filaments and the demonstration of open gaps and overlapping endothelial cell processes, as well as by the absence of a basement membrane and "fenestrations" typical of the endothelial cells of blood capillaries. Although large lymph vessels were observed in the submucosa, lymph capillaries were found only in the deep lamina propria adjacent to and within the muscularis mucosae. The upper and middle levels of the lamina propria of the gastric mucosa contained no lymph capillaries. The entire mucosa showed a rich supply of blood capillaries, many of which were adjacent to the basal lamina of gastric glands and the surface epithelium. These morphologic findings correlate with clinicopathologic observations on early gastric cancer. The particularly low incidence of lymph node metastases in the subtype of early gastric cancer that remains confined to the mucosa may be explained by the rarity of lymph capillaries in the mucosa. The high percentage of blood-borne metastases in recurrent early gastric cancer may be related to the rich vascularity of gastric mucosa.