How to Perform Endoscopic Ultrasonography in the Pancreas, Bile Duct, and Liver

Pancreas

Successful pancreatic imaging requires the ability to image the entire gland. In general, the body and tail of the pancreas are imaged through the posterior wall of the stomach, and, in most cases, the transgastric approach provides images of the genu (neck) of the pancreas as well. Complete imaging of the pancreatic head, however, requires placement of the transducer in three different positions within the duodenum: the apex of the duodenal bulb (the apical view), directly opposite the papilla (“kissing the papilla”), and distal to the papilla to visualize the uncinate process. This organized, station-based approach to pancreatic imaging is critical for individuals who are just learning or who have limited experience with endoscopic ultrasonography (EUS). Although the stations are the same for radial and linear endosonography, the images produced are different, as are the techniques for maneuvering the echoendoscope. As a result, representative images and illustrations from the various stations are presented for radial and linear echoendoscopes. As the reader is learning these techniques, it is also important for him or her to refer to the corresponding videos. Obtaining complete, accurate, and high-quality images of the pancreas and biliary tree represents the most difficult task facing the endosonographer.

Evaluation of the Body and Tail of the Pancreas

The examination of the body and tail of the pancreas begins by positioning the tip of the echoendoscope just distal to the squamocolumnar junction. From this position, the aorta is easily located and becomes the “arrow” that points the way. When the radial scope is used, the aorta is round and anechoic. With the linear scope, the aorta fills the screen as a long, anechoic structure extending across the entire monitor.

Radial Echoendoscopes

With the tip of the endoscope just distal to the squamocolumnar junction, the endosonographer inflates the balloon and positions the transducer in the center. The aorta is located, and with the endosonographer in a comfortable position (neither body nor scope shaft twisted or torqued), the aorta is electronically rotated to the 6 o’clock position ( Video 12.1 ). At this point, one usually sees a hypoechoic structure that moves from the esophageal wall and wraps partially around the aorta; this comprises the diaphragmatic crura. From here, one simply advances the echoendoscope while the aorta is kept in its cross-sectional conformation; the aorta must not be allowed to elongate. If the aorta is seen to elongate on advancement, it is an indication that the tip of the echoendoscope is being pushed laterally or is embedding in the gastric wall (often within a hiatal hernia pouch). If this occurs, the tip must be realigned and the maneuver repeated because it is important to keep the aorta in its round configuration. If this maneuver fails repeatedly, the echoendoscope should be advanced beyond the hiatal hernia and withdrawn. This maneuver helps one to visualize first the portal vein confluence (at the 6 o’clock position), and then the pancreas.

Video 12.1

Evaluation of the Body and Tail of the Pancreas Using a Radial Echoendoscope

With advancement, when the crura disappear, the celiac trunk is seen to emerge from the aorta and tract toward the transducer ( Fig. 12.1 ). In some cases with the radial scope, one first sees the splenic artery as a round, anechoic structure adjacent to the transducer. In this case, one just advances 1 to 2 cm, and the splenic artery traces into the celiac trunk. The celiac artery bifurcates into the hepatic and splenic arteries; with the radial scope, the bifurcation can look like a whale’s tail ( Fig. 12.2 ). Slight advancement of the scope beyond the celiac artery takeoff produces images of the body of the pancreas. The pancreas is seen directly below the transducer. The pancreatic parenchyma is usually slightly hypoechoic relative to surrounding tissue and has a homogeneous “salt and pepper” appearance. From this position, deep to the pancreas is an anechoic structure that looks like the head of a golf club. This is the portal vein confluence and is often referred to as the club head ( Fig. 12.3 ).

Once the club head has been identified, it becomes relatively straightforward to image the rest of the body and tail of the pancreas. Clockwise torque and withdrawal of the scope will trace the tail of the pancreas. It may also require some “right” adjustment on the left-right knob. During this maneuver, the left kidney comes into the picture as a large, oval structure with a hypoechoic, homogeneous outer “shell” (cortex) and an inhomogeneous, echo-rich central portion (medulla). The kidney roughly marks the body-tail junction of the pancreas ( Fig. 12.4 ). On further withdrawal, one sees the splenic artery and vein course right below the transducer, and a homogeneous, echo-poor bean-shaped structure occupies the right side of the image. This is the spleen, and the splenic vein and artery can be seen to insert into the splenic hilum. Once this image is seen, the examination of the distal body and tail is complete. From the tail of the pancreas, one simply reverses the maneuvers by advancing the scope, torquing counterclockwise, and returning to the portal vein confluence. From here, further advancement and counterclockwise torque allow imaging of the genu (neck) of the pancreas. The pancreatic duct is seen to dive away from the transducer as it courses through the neck. During the movements mentioned earlier, some left and right tip deflection may be required to obtain an elongated view of the pancreas. Once the elongated view of the pancreas is achieved, very slow and purposeful advancement and withdrawal of the scope demonstrate the entire width of the pancreas, including the pancreatic duct.

In the station approach, if one cannot see the typical landmarks that characterize the station during the course of the examination (no matter which station one is working on), one should return immediately to the starting point for that station and repeat the standard maneuvers. In the case of the pancreatic body and tail, this means returning to the gastroesophageal junction, tracing the aorta until the celiac trunk is seen, and so forth. A particular station should be examined as many times as required until the endosonographer is comfortable that the examination is complete. Sometimes, however, despite repeated attempts, one cannot achieve the imaging goals of a particular station. In this case, the endosonographer can continue the examination by going to other stations and then return later to the difficult station. Often, the return examination is successful.

Linear Echoendoscopes

Examination of the pancreatic body and tail with the linear scope follows the same basic approach as with the radial instrument. The examination begins at the gastroesophageal junction ( Video 12.2 ). In this case, however, the endosonographer must torque the scope shaft in a clockwise direction until the aorta is seen. Using the up-down dial, the aorta should gently slope down from right to left. Just as with the radial scope, the diaphragmatic crura are seen as a hypoechoic structure between the transducer and the aorta. This landmark is important because, as one advances the scope, the celiac trunk takes off soon after the crura disappear ( Fig. 12.5 ).

Video 12.2

Evaluation of the Body and Tail of the Pancreas Using a Curvilinear Echoendoscope

Unlike the radial scope, with which scope advancement is a passive maneuver (because of its 360-degree image), the linear scope must be gently torqued clockwise and counterclockwise to visualize the side of the aorta. Not uncommonly, the celiac trunk comes off the side of the aorta, and one can pass right by it if not systematically scanning back and forth. Once the celiac artery has been identified, it is traced until it bifurcates. Once the bifurcation is identified, and with 1 to 2 cm of further advancement combined with a gentle “down” on the up-down dial (“big dial away from you”), the pancreas and portal vein confluence come into view. From here, clockwise torque and withdrawal image the pancreatic body and tail ( Fig. 12.6 ), and counterclockwise rotation and advancement provide images of the genu ( Fig. 12.7 ). As with a radial echoendoscope, the pancreas should be traced all the way to the tail, which is confirmed when the splenic hilum is seen. As with all aspects of linear array imaging, gentle clockwise and counterclockwise torquing is mandatory throughout the examination to obtain complete imaging. Left and right tip deflection is of minimal importance when the linear echoendoscope is used.

An alternative technique used to examine the body and tail of the pancreas when using a linear array echoendoscope is to first differentiate the left lobe of the liver from the body of the stomach. From this position, when the shaft of the echoendoscope is torqued 180 degrees clockwise, the body of the pancreas can be identified and the gland traced all the way to the tail, as described earlier ( Video 12.3 ). A similar approach is to identify the portal vein as it enters the liver. Advancing the scope combined with clockwise torque enables one to follow the portal vein until the confluence is reached. Once the “club head” is identified, the pancreas will be between the portal vein confluence and the transducer (see Video 12.3 ).

Video 12.3

Evaluation of the Body and Tail of the Pancreas Using a Curvilinear Echoendoscope by Adopting Alternative Techniques

Evaluation of the Head and Uncinate Regions of the Pancreas

To examine the entire head of the pancreas confidently, all three positions (the apex, papilla, and distal to the papilla) should be achieved. The most efficient position is the apex of the duodenal bulb, because from this position most of the pancreatic head, distal bile duct, and portal vein can be seen together. As with other stations, positioning is the same with radial and linear scopes, but the subtle maneuvers to optimize imaging and the pictures produced are different.

Head of the Pancreas

Radial Echoendoscopes

This position allows imaging of the entire head of the pancreas (sometimes with the exception of the uncinate process) and also includes efficient imaging of the distal common bile duct. The radial echoendoscope should be slowly advanced through the stomach and allowed to bow along the greater curve. Once the pylorus has been visualized, the tip is advanced through the pylorus, at which point air is instilled into the duodenal bulb and some gentle downward deflection is applied to the tip of the echoendoscope ( Video 12.4 ). This maneuver allows direct endoscopic visualization of the apex of the duodenal bulb. Once the apex is visualized, the tip of the echoendoscope should be advanced until it is at the level of the apex. The balloon is then inflated until it gently occludes the lumen of the duodenum ( Fig. 12.8 ), and any residual air is aspirated from the duodenal lumen (all done under endoscopic control). At this point, EUS imaging commences, and the endosonographer turns his or her attention to the EUS image, first looking for the liver. Once the liver has been identified, the image should be electronically rotated (do not torque the scope) such that the liver is positioned in the upper left-hand corner of the screen. This technique provides uniform orientation and allows the endosonographer to identify the normal and abnormal structures more easily. When the liver is in the upper left-hand corner, the head of the pancreas is at the 6 o’clock position, and the bile duct is seen as an anechoic tube lying close to the transducer and coursing from the liver down to the 6 o’clock area.