At first glance, radial EUS of the normal mediastinum is deceptively straightforward and simple, given the linear nature of the anatomy. But this belies a lot of subtlety around the EG junction and also looking at the trachea more proximally. Given that we have a straight scope in a straight lumen, it is relatively easy to predict where key structures will lie as we withdraw the scope. At the EG junction, it is important to identify both the aorta and also the crus, and then just above this level, it is key to identify the spine and differentiate it from the thicker white line of the right pleura. Upon further withdrawal, the left atrium comes into clearer view, and then the left pulmonary vein is seen to extend from this. Both the azagus vein and the smaller thoracic duct come into plain view in the mid-esophagus. A key structure that may not be so obvious is the trachea, noted at about 25 or 26 centimetres. The EG junction is not necessarily a skill that comes easily and really does require practice, given the long, rigid tip of the scope. Part of the skill in passing a scope is obviously identifying visual landmarks like the cords at 12 o'clock, but more importantly is getting a feel for how the scope plays in the back of the throat. You will see from this video that it takes a couple of attempts to actually pass the scope down into the esophagus. This was mainly because it felt as though the scope was catching at the back of the throat. As ever, it's always best to err on the side of caution. Passing the scope along the esophagus, it is possible to get reasonably good mucosal views, and these are always better than those obtained at the end of the procedure. It's also very important to torque the scope up to the left of the OG junction to look at the fundus, because inverting the stiff distal tip of the echoendoscope is not possible. Orientation is extremely simple and mirrors that of a CT scan, with the patient's right-hand side appearing to the left of the screen. Examination usually begins at the level of the EG junction, and one important anatomical feature to identify here is the left cruise. This is seen as a grey band-like structure between the aorta and the esophagus. Two points about the cruise. The first one is that in order to see it, there must be a space for it to appear between the aorta and the esophagus. So if I'm looking at the screen, you see the aorta cheek-by-jowl with your scope tip, then it's unlikely you're going to see the cruise. You need to advance the scope slightly into the stomach, creating that space. The second point is that what we usually call the left cruise is actually an extension of the right cruise extending up in a sigmoid fashion to the left of the esophagus. The right leaflet of the diaphragm is usually less obvious and is seen in the space between the esophagus and the liver to the left of the screen. At the EG junction, we see the very important aorta, which should be rotated to 5 o'clock, thus mimicking CT scan appearances. And then to the left of the screen, often the IVC, though this may be obscured in the mists, and then also the left lobe of the liver. At about 2 o'clock to the scope, the air-filled and multi-layered appearance of the fundus of the stomach is usually seen. As you pull back into the oesophagus, keep an eye out for any evidence of multi-layers of black and white, which might represent a small hiatus hernia. This is usually very obvious when compared with the single wall layer pattern of the normal oesophagus, seen here to the left-hand side of the screen. Pulling back slightly into the distal oesophagus, the two important structures to identify are the spine, and then the much more obvious right pleura, with evidence of air shadows in the right lung, out to the left of this. At first glance, we see nothing but a flurry of indistinct white lines, but with some care to attention, it is possible to slowly pick out the key anatomical features, such as the vaguely, dimly outlined spine, and then the more obvious right pleura, right lung, and air in the left lung, seen to the right-hand side of the screen. At just above this level, the left atrium, although indistinct, starts to come into view. If one extends the range on the ultrasound, it's also possible to see deeper heart structures, such as the aortic valve. When we reach the mid-oesophagus, the two dominant features are the thoracic duct, and also the azygous vein. The thoracic duct is seen as a small, dark dot to the left of the screen, and then to the right of this, the much more prominent azygous vein runs up along the right pleura. Occasionally, the azygous vein can be seen to enter the superior vena cava, though often not. It's at about this level that the left atrium becomes much more distinct, and we can also see the left pulmonary vein extending down to the right side of the screen, almost like a bird's beak around the tip of the scope. Once we have withdrawn to about 25 centimetres and the level of the aortic arch, it's important to keep an eye out for the indistinct air-fill structure to the left, which is the trachea. If we slowly advance the scope again, we can see this air-fill structure to split into the left and right main stem bronchi and other airways. Above 18 centimetres, and when we start inspecting the structures of the neck, an over-inflated balloon can become uncomfortable for the patient. Orientation in the neck is again relatively easy, with the trachea at 12 o'clock and the spine at 6 o'clock. The neck vessels are obviously the key structures seen, with the two carotids appearing like rivets, and then behind this, to the right-hand side of the screen, the left subclavian. The thyroid lobules may also be seen. Given the straight-line withdrawal of the EUS scope, it is not surprising that a CT scan anatomy mimics that seen on the EUS screen directly. Here we see the scope position outlined by a red dot. Given the lack of resolution, it's not surprising that we don't see the right pleura on the CT, but the relative position of the spine is well outlined. At the level of the mid-esophagus, the left atrium is well seen, as is the left pulmonary vein. Out more peripherally, we can also see the aortic outflow tract, as it would be seen at EUS. To the left of the aortic arch in the screen, we see the void that represents the trachea and the main stem bronchi. Neck vessels appear as with the EUS. Scanning at the EG junction, we identify the aorta and also the two elements of the cruci holding the distal esophagus. On slow withdrawal, the very prominent bright line of the right pleura is seen, and then also anterior to the scope, we see the early part of the left atrium. At around 29 or 30 centimetres, we begin to see the very prominent azagus vein, as it starts its journey along the bright white right pleura to reach the superior vena cava. To the left of the aorta on the screen, we begin to see the small black dot that is the thoracic duct. The left atrium is always quite prominent, as is the left pulmonary vein. If we increase the range of the EUS view, the aortic valve and the aortic outflow tract will begin to come into view at about 11 o'clock on the screen. When we begin to see the aortic arch forming, it's time to look out for the trachea, which is seen as a series of air-filled rings to the left of the arch. If we slowly push the scope back in from this point, we can see the trachea splitting into left and right main stem bronchi, although usually this is quite indistinct. Above the arch, the left subclavian comes into view. And then above this level, the carotids can be seen, with the internal jugular more peripherally. Further up in the neck, the lobes of the thyroid become visible. One anatomical variant that can be seen is an aberrant right subclavian artery, giving rise to dysphagia lussoria. In this patient, as we come above the aortic arch, we see a vessel running to the left of the screen, which is an aberrant right subclavian. It's easy to imagine how one might get dysphagia with this. An extremely rare anatomical variant is situs inversus. While watching this recording, keep an eye on the aorta, and see how it very gradually tracks to the left-hand side, or right-hand side of the patient, as the scope is withdrawn.

radial EUS

mediastinum

esophagogastric junction

anatomical features

ultrasound orientation