The two basic techniques for examining the stomach are the balloon inflation procedure and the water-filled stomach method. Both methods can be employed with either the linear or radial echoendoscope, but examination with the radial scope is easier and more efficient because of the larger viewing field. The balloon inflation method is preferred for rapid screening of submucosal lesions and the examination of perigastric structures ( Fig. 10.1 ). The water-filled method is best for examining the gastric wall layers and the careful and accurate evaluation of specific lesions ( Fig. 10.2 ). With the balloon inflation technique, the tip of the echoendoscope is advanced to the immediate prepyloric antrum. The balloon is fully inflated and continuous suction is applied to remove air from the gastric lumen. When the gastric wall is completely collapsed around the balloon, the balloon is centered as well as possible, and slow withdrawal is performed ( Video 10.1 ).
Video Demonstrating the Balloon-Inflation Method for Examining the Stomach Using a Radial Echoendoscope
When one is learning endoscopic ultrasonography (EUS), it is critical that images are displayed in a standard orientation. In the case of gastric imaging, the liver is easily recognized and should be electronically rotated until it is positioned in the 9- to 12-o’clock space. This orientation will cause the pancreas to emerge at the 6-o’clock position on withdrawal, and the spleen and left kidney will appear between 12 and 4 o’clock. The examiner’s eyes should then be fixed on both the gastric wall and the perigastric structures. If a lesion or abnormality is recognized, specific maneuvers can be applied to obtain detailed imaging.
With the water-filled method, the stomach is collapsed (removing all air), and 200 to 400 mL of fluid is instilled into the gastric lumen (see Fig. 10.2 and Video 10.2 ). High-quality imaging of the gastric wall requires attention to detail on two points: (1) the transducer must be positioned at a perpendicular angle to the gastric wall or a specific lesion ( Video 10.3 ) and (2) the tip of the echoendoscope must be positioned within the focal zone of the transducer (see Chapter 1 ). This second point is absolutely critical when using the mechanical radial echoendoscope but is less important with electronic radial instruments. To obtain superfine images with the water-filled method, one should consider using an agent to paralyze peristalsis and instill water into the gastric lumen in a way that minimizes the production of microbubbles (slow infusion versus a water jet technique).
Video Demonstrating the Water-Filled Method for Examining the Stomach Using a Radial EchoendoscopeVideo 10.3
Radial Endoscopic Ultrasonography, Performed After Instillation of Water, Reveals a T1 Gastric Cancer Confined to the Mucosal Layer
The difficulty or impossibility of obtaining perpendicular images in some areas presents a significant challenge in gastric EUS. An example is the gastric antrum. It may be impossible to adjust the tip deflection in a way that positions the transducer perpendicular to the antral wall while at the same time not pressing the transducer against the wall. The consequence of an inability to achieve optimal orientation between the transducer and the surface of the stomach is tangential imaging. If the ultrasound waves pass tangentially across the gastric wall, the layers will appear abnormally thick. This appearance can lead to overstaging of early gastric cancer or inaccurate determination of the layer of origin in submucosal masses. With large bulky tumors, where one is trying to differentiate stage T3 from stage T4, this is less of an issue than with very superficial lesions in which one is trying to determine whether endoscopic mucosal resection (EMR) is appropriate. In the antrum, it is sometimes easier to use a dual-channel endoscope and a high-frequency catheter probe to achieve good positioning ( Video 10.4 and Fig. 10.3 ). However, if the lesion is large, the depth of penetration of the catheter probe will be insufficient for accurate staging.