Hey, everybody, it's Rishi Agrawal and in this video, I'm
going to show you how I look at a lateral chest x ray.
Now, this is not going to be an exhaustive list of the anatomy
because I want to save that for another longer video.
But I'm going to cover the basics here.
Most of the time, the abnormalities you'll see on chest
x ray will be on the frontal view and you'll use the lateral view
to localize lesions.
But sometimes there's lesions that are more obvious
on the lateral view, and occasionally you'll even have lesions
that you can only see on the lateral view and not on the front of you at all.
So when I open up a lateral chest x ray,
the first thing that I look at is this area right here.
And this is where the right and left hila are superimposed over each other.
And there's an important landmark in this area, and that is
this lucency right here.
That's the left upper lobe bronchus.
The reason why that's important is
because it serves as a landmark for other anatomic structures.
So just anterior to the left upper lobe
bronchus is this structure right here.
And it's kind of a rounded structure.
And that is the right pulmonary artery.
And then kind of arching over the left upper lobe
bronchus is another vessel.
And you might guess what that is.
So we have there right over here, this is the left
pulmonary artery.
OK, so if you imagine this as a clock face,
then the right pulmonary artery takes up the 9:00 position and the left
pulmonary artery goes from like 10:00 to about 3:00.
And inferior to the left upper lobe bronchus,
you have this sort of lucent area,
and that is normal.
That is called the infrahilar
window.
If you see opacity in that area,
then usually what you're looking at is hilar or mediastinal lymphadenopathy.
OK, so normally it's that area is lucent. OK.
So the next thing that I look at after I've looked at the hila
are the clear spaces.
And there's three clear spaces on the lateral radiograph.
The first one that I look at is right here,
and it is just behind the sternum.
So this is appropriately named
the retrosternal
clear space.
And if I see abnormality in that area, it could mean
that there's airspace disease in one of the upper lobes.
Or it could also mean that there's an anterior mediastinal mass.
The next place I look is behind the trachea.
So the trachea is this lucent structure right here.
And just behind that is another clear space.
And it's bordered posteriorly by the spine, inferior
really by the aortic arch and anteriorly by the trachea.
This is called the retrotracheal
clear space or
retrotracheal triangle, or it's also called Raider's triangle.
You might hear that term.
Usually in that area, it's vascular anomalies,
like an aberrant right subclavian artery can show up in this area.
And you can have other vascular anomalies here.
Or you can see abnormalities with the esophagus
because the esophagus lies just posterior to the trachea. OK.
And then the third clear space is down here
and is just behind the heart.
And the superior border of it is a little bit
ill defined so I'm just going to draw that as a dotted line.
And this is called the retrocardiac clear space.
And in that area, commonly you'll see
lower lobe consolidation or you might see masses.
And this is also where you'll see a hiatal hernia.
So those are the three
clear spaces of the lateral chest x ray.
After I've looked at the clear spaces,
the next thing I do is I look at the heart.
So on the lateral view,
the right ventricle sits right here. OK.
This is the right ventricle.
And in this patient, notice that the right ventricle only comes up
to approximately like a third
of the way up the sternum.
OK, so in other words, this is the whole sternum and manubrium here.
And this is like two thirds of the manubrium and sternum are here,
whereas the rest down here is approximately one third.
And that's normal.
When the right ventricle starts to encroach upon the retrosternal clear
space and go this way, then that's a sign of right ventricular hypertrophy.
OK, so that's right ventricle.
And then we have the left ventricle back here.
OK, this is the posterior border of the left ventricle.
And in a patient with left ventricular hypertrophy, the retrocardiac clear space
becomes much smaller because the left ventricle moves out in that direction.
The main pulmonary artery and the ascending aorta are not really things
that you can evaluate well on the lateral view,
and that's because they're partially superimposed over each other.
Occasionally, residents will try to measure the aorta by going from
here to here.
But you can't really do that because some of this opacity
is the pulmonary artery and some of it is the aorta.
It is common to see aortic enlargement if it involves
the distal part of the arch, which is here,
or the descending aorta,
which is about right here.
A lot of times in older patients, the descending aorta is tortuous
and that shows up on the lateral view.
And then sometimes you can see aneurysms of the descending aorta
on the lateral view, too.
The next thing I look at are the bones, and mainly
on the lateral view, I'm looking at the spine.
The spine and the vertebral bodies show up really well on the lateral view.
So I'm looking back here
making sure that there's no vertebral compression deformities.
And I'm looking at the sternum anteriorly here
because a sternal fracture is virtually impossible to see on the frontal view.
The lateral view isn't
really good for looking for rib fractures, although occasionally you do see them
and then occasionally you also see fractures of the scapula.
So here's one of the scapula right here.
And then the other scapula is right here.
After I'm done looking at the bones,
the next thing that I do is I look at the diaphragm.
So the diaphragm is, of course, right here.
I have another video with a few different ways
on how to tell the right from the left side of the diaphragm.
So I'm not going to go over that here.
But while I'm looking at the diaphragm,
I'm looking at the costophrenic angles which are back here, posteriorly.
And remember that if you have blunting
of the posterior costophrenic angles, that's a sign of pleural effusion.
Also, remember that the lateral view is much more sensitive for detection
of small amounts of pleural fluid compared to the frontal view.
And then finally, after I'm done looking at the diaphragm,
I look below the diaphragm to see if I can see
abnormalities in the upper abdomen.
All right.
So that's been a quick overview of how I look at a lateral chest x ray.
If you have any questions
about this topic or any other chest topic, let me know in the comments below.
Thanks.