A fundamental study of normal layer structure of the gastrointestinal wall visualized by endoscopic ultrasonography.

The gastrointestinal wall could be separated into five layers or nine layers by means of the ultrasonic endoscope, and the histological structure of these layers was ascertained by comparing endoscopic ultrasonograms of resected specimens of the gastrointestinal tract with their corresponding histology. The results were as follows: With five layers of the gastrointestinal wall, the first and the second layer corresponded to the mucosa, the third layer was the submucosa, and the fourth layer corresponded to the muscularis propria. The first layer was a border echo demonstrated inside the mucosa. The fifth layer consisted of the serosa and a border echo visualized outside the serosa. When a thin layer was visualized at the same time in both the second and the fourth layers, the gastrointestinal wall was separated into nine layers in total. With nine layers of the gastrointestinal wall, the muscularis mucosae was composed of a thin layer in the second layer and a narrow layer between a thin layer in the second layer and the third layer. A thin layer in the second layer was a border echo visualized inside the muscularis mucosae. A thin layer in the fourth layer of the gastrointestinal wall consisted of a border echo and a connective tissue between the inner circular muscle and the outer longitudinal muscle.