Standard Imaging Methods Using a Convex Ultrasonic Endoscope for EUS-FNA

To recognize the locations in the mediastinum, you will need to know the height and left/right indices. The indices for height are — from inferior to superior — the inferior vena cava passing through the diaphragm (boundary between the abdomen and mediastinum), tracheal bifurcation, aortopulmonary window (AP window), arch of azygos vein, and aortic arch. The left/right index is the trachea.

After inserting the scope in the distal gastric body, observe the abdominal aorta by turning the scope clockwise. Follow the abdominal aorta towards the superior side while pulling the scope to confirm the celiac artery bifurcation. Observe the lymph nodes around there.

As you slightly withdraw the scope from the celiac artery bifurcation, a long and narrow low-echo image is imaged immediately above the aorta. This is the crus of the diaphragm and serves as a reference to let you know the boundary between the abdomen and mediastinum.

Now turn the scope counterclockwise to image the left hepatic lobe. While slowly withdrawing the scope, follow the left hepatic vein that appears towards the upper screen. This enables you to observe the inferior vena cava.

By following the inferior vena cava towards the superior side while slightly withdrawing the scope, you can observe the inferior vena cava passing through the diaphragm. This is the boundary between the abdomen and mediastinum (red line). On the screen, the mediastinum is on the right side of this border.

While viewing the inferior vena cava, slowly pull the scope and turn it clockwise. This allows you to visualize from the inferior vena cava to the right atrium as well as the left atrium, left ventricle, and ascending aorta. The pulmonary artery is also imaged on the bottom of the same screen.

When you follow the pulmonary artery towards the transducer side while pulling the scope, the cross section of the right pulmonary artery will emerge. The tracheal bifurcation is found in this region. Repeat the counterclockwise rotation and clockwise rotation of the scope in this position to visualize multiple linear echoes. This enables you to accurately identify the tracheal bifurcation.

As you pull the scope from the tracheal bifurcation, you will be able to identify the trachea visualized as multiple linear hyperechoes.

Withdraw the scope slowly to follow the trachea towards the superior side (right side of the screen). While doing this, turn the scope counterclockwise and angulate it upward to visualize the cross section of the right pulmonary artery on the left side of the screen and the cross section of the aortic arch on the right side. The region sandwiched by these two vessels is an area called the “AP window”.

Withdraw the scope further to identify the artery that branches from the aortic arch. Usually, the clockwise rotation of the scope will first visualize the left subclavian artery, then the left common carotid artery, and the brachiocephalic artery on the right side.

Using the descending aorta as the start point and end point, observe the posterior mediastinum circumferentially by turning the scope clockwise or counterclockwise. Doing this at various heights makes it possible to observe the entire area of the posterior mediastinum.

Turn the scope clockwise from the descending aorta on the level of the inferior mediastinum to image the left heart system.

Turn the scope clockwise some more at the point where the left heart system is visible. You will be able to recognize the azygos vein and vertebral body.