The recent escalation of reported cases of acute lung injury from vaping underscores the need for interpretation skills when diagnosing toxic inhalation pneumonitis or other acute pulmonary conditions.
Whether caused by an intentional exposure to inhalants, by chemical spills, occupational exposures, or by the current smoke from California wildfires, recognition of parenchyma pneumonitis and other common pulmonary conditions is key to early and more effective management.
You can review your pulmonary imaging and study interpretation skills through K2P’s series on pulmonary testing.
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Reading Chest X-Rays (CXRs)
Faculty: Darlene R. Nelson, MD
Our objective for this talk will be to review the fundamentals of reading a chest X-ray.
Why should you ready your own CXRs?
You should read your own chest X-ray because most of the time a lot of us get those interpretations back from radiology quite quickly and you may be tempted to not actually look at the film yourself. So you know the history and the exam and the radiologist doesn't.
It's important to remember that a radiologist reads a chest X-ray in less than 20 seconds generally. They do pick up most of the abnormalities quite quickly. But you know the history and specifically what you might be looking for that they may not. They do a miss somewhere about 10 to 20% of the abnormalities and that's just because, once again, they're reading them quickly and they see them so often.
I would also make a pitch just to be your patient's advocate. Once again, you ordered the test, make sure you look at the image to find out what may or may not be wrong.
General Guidelines in Reading a CXR
When you're looking at a chest X-ray, always make sure you know the stuff that's the right patient, what technique it was done with, was it done as an AP, was it a PA, was it a portable film?
All of these things make a difference in how you would interpret the images. Try to have a consistent approach and I'm not going to advocate for any approach over another. I'll show you the approach that I tend to use just as one example. But certainly, you just want to be consistent in how you're looking at X-rays to not miss things. And then finally again, my other big push here is to look at old films, old films, old films, they are your biggest friend.
Something that seems like a calcified nodule, if it's been there for 20 years, you don't need to worry about it. You don't need to call the pulmonologist to get a CT scan and potentially a biopsy. If it's new in the last year or if you never noticed it before, then it does need further workup. So these are things that old films can really help you out with.
I first generally look at the extrapulmonary structures and what you can pick up here sometimes is things like destructive arthritis, you can find that they have an absence of a brush shadow for one reason or another. You may see prior surgeries or valvular prostheses.
Then I tend to look at infradiaphragmatic abnormalities. You look for a gas air bubble, whether or not they got fluid below the diaphragm. I look for skeletal changes then, you can pick up lytic lesions here, rib fractures, all things when you're maybe seeing a patient in your clinic with that question of shortness of breath or chest pain. I then evaluate for mediastinal structures and here, we'll talk a little bit more as we look at chest X-rays about silhouette signs and what is normal and abnormal. But you can pick up things like pericardial fluid and lymphadenopathy.
You want to look at the plural region, in particular, you want to look at the costophrenic angles and see if there's blunting or calcification, which might suggest a prior exposure to asbestos with calcification or whether or not they have pleural effusions.
Then you want to finally look at the lung parenchyma, it's what generally people like to jump to first. But here you want to take a systematic approach and you can look again for nodules, air bronchograms, consolidation, carefully look at both sides and compare one to the other.
The Importance of the Lateral View
And finally, don't forget the lateral view. So this is another striking x-ray that I saw a few years ago where the patient's PA view looks very normal, but on the lateral, you can see if they have a lot of retrosternal gas. And on a CT scan here, this was a large septic embolus from his left upper lung and he ended up having a resection and pleurodesis. But you would totally have missed that if you'd have only looked at the PA view.
Normal Lung Structures
Okay, so where are the normal lung structures on the chest x-ray? So right along here, this is the borderline of the right upper lobe. This would be your right middle lobe and your right lower lobe, you're only catching here. Because you have to remember the lobe sits obliquely more in the chest.
And so you're really only catching the border of the right lower lobe down here on the standard PA. The left upper lobe is right up in here. This is where the lingula shadows against the heart and the left lower lobe against the diaphragm.
Other mediastinal structures that you want to look for when you talk about these silhouette signs. On the right here, you can see this stripe is where the right innominate vein is. So if this is enlarged, if there's an abnormality there, it may involve that. The superior vena cava is right here.
The ascending aorta comes up here. So in someone with dilation of her ascending aortic aneurysm, sometimes you can see this come out way out like this. This is where the right atrium lies. So in someone with tricuspid regurg or dilated right atrium, this can often be bowed out like that.
This is also where you can catch a lot of retrocardiac fat that can also make this look enlarged. This is diaphragm as you know bilaterally. Your descending aorta is right here, left lateral ventricle, left pulmonary artery is right here.
This is what's commonly referred to as an aortic pulmonary window. So if this normally makes a nice angle right here between your aorta and your pulmonary artery. If this area is gone or it looks darker than it should be, often this just means lymphadenopathy. This is where one of your mediastinal lymph nodes sits. Aortic arch and then your left innominate main.
On the PA x-ray, it's really hard to see the fissures unless there's fluid in them. Remember on the right lung you have three lobes, you have your right upper, your right middle, right lower. So you have a minor fissure and a major fissure. And the major fissure is really obliquely in the chest, which I'll show you on the next slide.
So you just catch the major fissure down here and this would be the minor fissure. On the left lung you only have a left upper lobe and left lower lobe, so you only have a major fissure.
As you can see on the lateral, this is where the major fissure lies and how it sits obliquely in the chest. So your left lung or your lower lobes go all the way from the base of the chest up to the top of the chest.
When you're looking at the lateral, you want to think about its super…it's...the right lung and the left lung are superimposed upon each other and you want to try to think about each lung separately. So you want to think about the major fissures being here. If you see something here, then you're thinking in the minor fissure which is in the right lung.
Clinical Pearls on CXRs
Take-home points on chest x-rays, first, read your own chest x-rays, hopefully of all, encourage you to do that again. Remember to be systematic, have a systematic approach every time you look at this so you don't miss things.
Look for what's normal so that you can pick up on what's abnormal. Look at old films, they're your best friend when looking at any radiographic image.