6.7). The triangular‐shaped ventral pancreas may appear more echolucent than the dorsal pancreas (DP) in about 75% of normal people and should not be mistaken for an echolucent tumor (Figure 6.6). The echolucency of the ventral pancreas can occasionally even be seen in views of the organ through the stomach. Further withdrawal reveals more of the pancreatic head where longitudinal views of the pancreatic duct may occasionally be seen (Figure 6.8). The confluence of the superior mesenteric vein with the portal vein and splenic vein is seen deep to the pancreatic head (Figure 6.9). This is an important view for examining splanchnic venous involvement by pancreatic head malignancies. As the echoendoscope comes around the junction of the second and first portion of the duodenum, small changes in orientation of the tip will result in major shifts in views. Sometimes the best views of the head of the pancreas are obtained when the echoendoscope first enters into the duodenal bulb with the scope in a long position. It is this orientation which most commonly provides a “stack sign” of the common bile duct (CBD) running parallel to the deeper main pancreatic duct (Figure 6.10). A stack sign can be demonstrated in more than 80% of patients with normal pancreatic ductal anatomy. When pancreas divisum exists (3–7% of normal people), a stack sign can only be demonstrated in about one‐third of patients. Instead of the absence of a stack sign in pancreas divisum the more specific crossed duct sign may be seen. The crossed duct sign results from the CBD being seen in cross‐section while the pancreatic duct, draining to the minor ampulla, is seen in longitudinal section.
Figure 6.1 Radial EUS: pancreatic body and portal/splenic vein confluence. PV, portal vein; SMA, superior mesenteric artery; SV, splenic vein.
Figure 6.2 Radial EUS: portal/splenic vein confluence. PV, portal vein; SMA, superior mesenteric artery; SV, splenic vein.
Linear examination of the pancreas
The linear endosonographic examination of the pancreas through the stomach differs fundamentally from the radial examination in that complete imaging of the pancreas must be provided by rotating the shaft of the scope. Since the retroperitoneal structures are all posterior to the stomach, clockwise (rightward) rotation of the echoendoscope will point the echoendoscope towards the patient’s left and counterclockwise (leftward) rotation towards their right side. To find the pancreas in the stomach, one starts at the abdominal aorta near the gastroesophageal junction and follows its course distally until the take‐off of the celiac artery is visible. Usually, the more oblique take‐off of the superior mesenteric artery is apparent just distal to this. Further advancement of the instrument distally will find the pancreas neck/body nestled between the “V” of the celiac and superior mesenteric artery. The splenic artery will course tortuously in and out of the pancreas body/tail, but the splenic vein usually has a straight course and is the larger, deeper and more ovoid of the two vessels (Figure 6.11). The pancreas is interrogated sequentially from the neck to the body and tail through the stomach at this level by rotating the echoendoscope to the right (clockwise) with slight withdrawal following the splenic vein and splenic artery as they run into the hilum of the spleen. The pancreas neck, body, and tail will appear be the tissue found between the splenic vein and the posterior gastric wall. The pancreatic duct is usually seen in cross‐section through the stomach (Figure 6.12). A normal caliber duct will appear as a small, sometimes difficult to see, echolucent dot in the middle of the pancreatic parenchyma. Rotation to the left at the level of the celiac axis and body of the pancreas brings into view the pancreatic neck with the portal vein confluence deep to it. The splenic vein merges into the confluence from the patient’s left and the superior mesenteric vein runs caudad from the portal vein confluence. A little further leftward rotation of the echoendoscope may produce views of the right border of the pancreatic neck looking down towards the pancreatic head. Sometimes, longitudinal views of the pancreatic duct can be obtained from this view.
Figure 6.3 Radial EUS: pancreas tail. PD, pancreatic duct; SA, splenic artery; SV, splenic vein.
Figure 6.4 Radial EUS: pancreas tail.
Figure 6.5 Radial EUS: pancreas neck. PD, pancreatic duct; PV, portal vein; SV, splenic vein.
Figure 6.6 Radial EUS: head of pancreas. DP, dorsal pancreas; VP, ventral pancreas.
Figure 6.7 Radial EUS: ampulla.
Figure 6.8 Radial EUS: head of pancreas. CBD, common bile duct; PD, pancreatic duct.
Figure 6.9 Radial EUS: head of pancreas, vasculature. CBD, common bile duct; PD, pancreatic duct; PV, portal vein; SMV, superior mesenteric vein; SV, splenic vein.
Figure 6.10 Radial EUS: head of pancreas. CBD, common bile duct; PD, pancreatic duct.
Figure 6.11 Linear EUS: pancreas body. PD, pancreatic duct; SA, splenic artery; SV, splenic vein.
Figure 6.12 Linear EUS: pancreas tail. PD, pancreatic duct; SV, splenic vein.
As with radial endosonography, the linear duodenum presents the endosonographer with the most variability in endosonographic relationships of vessels, ducts, and periduodenal organs. There is a marked transition in the direction of the scope tip and