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The radial array EUS examination through the duodenum follows a constrained path, but the endoscope can be rotated to put various structures into the inferior aspect of the image plane, as shown in the models of the duodenum, pancreas (brown), portal and superior mesenteric veins (blue), aorta (red), and SMA (silver). There are many structures of interest in a rather small area, and most of the images obtained are from the posterior view, with the liver to the right and the pancreas to the left of the image screen. After leaving the pylorus, the pancreas can be oriented with the tail pointed either to the left or inferiorly, and the splenic vein runs in the same direction as the pancreas. Going through the duodenal bulb, the gastroduodenal artery (GDA) often appears. Without Doppler, the GDA can be confused with the common bile duct (CBD) since these structures are nearly parallel in orientation and are very close to each other. As the apex of the duodenal bulb is reached, the image plane captures a longitudinal view of the CBD and the portal vein. As the descending duodenum is reached, the bile duct is seen in cross‐section and the IVC comes into view. As the third part of the duodenum is reached, the image plane rotates in such a way as to give a longitudinal cut through the IVC and then passes underneath the junction of the SMA with the aorta. Branches of the SMV can be found and the renal vein is visible in the “armpit” formed at the insertion of the SMA into the aorta. A special area is then highlighted in Video 1.5. Models show how the gastroduodenal artery and the hepatic artery (in red) relate to the CBD (in orange).

Figure 1.5 shows a model with an image plane and Figure 1.6 shows the resultant planar anatomy, which forms the stack sign – a phenomenon in which the portal vein, CBD, and main pancreatic duct are captured in the same field.