Problems and variations in the interpretation of the ultrasound feature of the normal upper and lower GI tract wall.

The aim of this study was to define the various ultrasound appearances of the normal upper and lower GI tract wall and to discuss current interpretations of the relationship between each echographic layer with the real anatomical structures. We studied a total of 70 patients by means of endoscopic ultrasonography and examined in vitro some surgical specimens of the normal stomach, colon and rectum. We found a 'five layer' structure at the level of the esophageal and gastric wall. This pattern was not recognized in the duodenum during the in vivo study. Our experimental results support the hypothesis that the first and fifth hyperechoic layers of the gastric wall are partially generated by ultrasound reflection at the interface liquid/wall and that the second hypoechoic layer corresponds to the deepest part of the mucosa. Important variations in the thickness of each layer were found in different conditions during in vivo studies. The fourth hypoechoic layer becomes very thin after water distension of the stomach. The in vitro investigation of the specimen of normal colon and rectum showed some different features. At this level it is sometimes possible to distinguish a separate very thin hypoechoic layer in the deepest part of the second layer, probably corresponding to the muscularis mucosae. The muscular layer is sharply divided into two distinct layers related to the circular and longitudinal muscular coats.