Normal EUS Images

On EUS, the GI wall appears in 5 layers (Figs 1, 2). Optimal imaging of the GI wall is essential to determine the wall layers affected by disease. With the sonographic plane oriented as close as possible to perpendicular to the intestinal wall, optimal imaging and limitation of artifacts can be achieved. EUS images of organs, large vessels, and lymph nodes contiguous to the GI tract each have their own characteristic appearance.

Seven standard positions [18] are described for EUS scanning in the upper GI tract. These positions include (1) horizontal duodenum, (2) duodenum around the papilla, (3) duodenal bulb, (4) gastric antrum, (5) body of stomach, (6) fundus, and (7) distal esophagus. The normal anatomy of esophagus, stomach, pancreas, retroperitoneum, and hepatobiliary tract have been described [15,19-22]. Orientation of the images of these various organs requires an understanding of landmark anatomical structures that can be imaged from these positions (Table 1). For the esophagus, the primary landmarks include the aorta, the spine, the left atrium, the carotid arteries, the azygous vein, and the carina (Fig 3) Landmarks for the stomach include the celiac axis, the diaphragm, the liver, the spleen, the gallbladder, the left kidney, and the pancreas. For the colorectal area, the prostate, the seminal vesicles, the uterus, the vagina, the urinary bladder, the levator ani muscles, and the coxygeal bone are the primary landmarks. For the hepatic pancreatic, and biliary organs, imaging from both the stomach and the duodenum is essential to locate the bile ducts, the gallbladder, the pancreatic duct, the celiac axis vessels, the superior mesenteric artery, and the portal confluence veins (portal, splenic, and superior mesenteric). An understanding of lymph nodes associated with each organ is also crucial to understanding where to scan for spread to regional lymph nodes (N stage).

By using these anatomical landmarks for orientation, pathology in the various organs can be imaged. In patients without gastric surgery, all landmarks can be located in at least 90%. However, scanning all organs completely would take more than 1 hour. Therefore, in any given examination, certain structures or areas may not be noted if the focus is a specific anatomical region.

^*Vessels and organs seen from each upper gastrointestinal location are listed in order of appearance as the echoendoscope is withdrawn proximally from the horizontal duodenum.

^bStructures usually seen well from the "withdrawn-wedged" position.