Interactive Transcript
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Okay, it's Mark and we're going
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to keep going with a bit of the
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ground glass sort of motif here.
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We're going to talk about the things
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that sort of mimic ground glass.
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Now, we're going to look at mainly a lot
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of things about expiratory views because
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that, to me, is one of the more common
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causes, like how can you tell something
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is an expiration on CT or on radiograph.
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And also kind of introduce you to the
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concept of using the DLCO, that's diffusing
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capacity or diffusing measurement
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of the pulmonary parenchyma, and that
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can be very helpful in distinguishing
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normal versus subtle ground glass.
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And then we'll kind of look at the
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differences of pleural effusion or
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underexposure from ground glass.
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There's a subtle difference
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that you can usually tell.
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So here's where we're going to be.
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So when we talked about ground
0:49
glass, we said, here are the five
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things that we should be doing.
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But the very first thing before we even
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get started is, is it really ground glass?
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Or is this a mimic?
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So, the problem with ground glass, and I'm
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going to tell you this to write up,
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there are people who are in sort of
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mid-expiration on like CTAs, and there's
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some subtle increased opacity. Is
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that ground glass or is that normal?
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And it's very
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no, I don't want to say embarrassing, but you
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know, it happens, you know, you don't want to
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tell a clinician, “Well, it could be ground glass
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diffuse lung disease or it could be normal.”
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No, no, so you kind of say, what are
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some ways we can figure this out?
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And the first is truly to kind of get
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an idea about what does it normally
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look like on CT or in radiograph
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during expiration. And then if you're still not
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sure, then you just, you kind of go, well, suggest
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a DLCO measurement or a repeat CT of full
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inspiration, and we'll see if this is real,
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and I think that's very reasonable as well.
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So, this is me, uh, consider me the gold
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standard. Got me all imaged, my lungs.
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So this is me in inspiration.
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Notice the bronchi. Then this is
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the key now: the posterior wall, the
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bronchi, and the trachea are rounded.
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When we breathe out,
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it flattens and even becomes a little
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concave. When it's concave, that tells
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you this is obtained during expiration.
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What happens to the lung
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parenchyma in expiration?
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Well, notice how it kind of looks
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like, oh, that's the dark bronchus sign.
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This is ground glass.
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Slow down.
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It's an expiration, and in normal expiration,
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the lung density gets higher, but it
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gets disproportionately higher as you go
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dependently, and that's kind of a key.
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As you go down, it should be brighter.
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That, to me, if I see that, I go, this is
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consistent with a normal expiratory period.
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Exam: so inspiration with trachea.
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It's rounded posteriorly. With expiration,
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it'll flatten or even indent. That's
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expiration, and when you see something that
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may be expiration, look for this gradual
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increasing density posteriorly.
3:01
That's all, that's all expected.
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What about for the radiograph?
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Well, first of all, don't count ribs.
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My God, people are like snowflakes.
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My lungs go down to T12.
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What does that tell you?
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Well, you know, I got big lungs.
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I have a rounded, uh, diaphragm.
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It's not hyperinflated, but what you do want
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to do is understand that the diaphragm is
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actually a weak muscle, but when we take a
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breath in, those stronger intercostal muscles
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just kind of widen out; they pull the ribs out.
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Now that is a lot less affected by what
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lung diseases and various other problems.
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So you want to start kind of looking at these
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exams, making sure they're the same view,
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AP to AP. Don't measure this intrathoracic
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width from a PA and apply it to the AP.
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That doesn't work.
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And you measure it from the
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inner rib, the widest part.
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If you have that comparison,
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this is the same patient.
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This is an expiration.
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This is not ground glass.
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It's expected increasing
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density and vascular crowding.
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Okay.
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Milne et al., uh, did a study in 1993 where they
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looked at all of these radiographs and they
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identified 120 patients with low lung volumes.
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When they dove in deeper to see why, they
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found that 105 of them had low lung volumes
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because of intra-abdominal changes,
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such as weight gain, pregnancy, or ascites.
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They also found 11 that were reduced
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because lung compliance was reduced.
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When you, say, have congestive heart failure
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or diffuse lung disease, the lungs stiffen.
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You breathe in.
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The intrathoracic cavity will still expand to
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the same amount, but the diaphragm, the weaker
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muscle, cannot descend to the same amount.
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And then they only found four patients
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where they felt, yep, this was actually a
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person who did not take a deep breath in.
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Uh, please avoid the term
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poor inspiratory effort.
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Looking at this, you'll find
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that of all of these patients, only
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four didn't take a deep breath in.
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If the lung volumes are low, there's
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an explanation there most likely.
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This patient has acute dyspnea and hypoxia.
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What's the main finding?
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Well, this person's lung volumes are low.
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Maybe it's
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you know, they didn't take as deep a breath.
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Well, when you measure the intrathoracic
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width, they're exactly the same.
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So they took in the same degree,
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but the diaphragm would not descend.
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The answer came about in 10 hours because they
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developed diffuse, sort of a patchy or, say,
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nodular but relatively uniform consolidation.
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This was an acute lung injury
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and this radiograph is the early
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manifestation of acute lung injury
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before the ground glass consolidation.
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It's the reduced lung compliance.
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If you had said poor inspiratory
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effort, you would have missed it.
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This patient has gradual increasing,
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shortness of breath over a year.
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You look and it's like, wow,
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is that the same patient?
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Must be an expiration scan.
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Is that ground glass?
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Or is that, Alexis?
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And it turns out the
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intrathoracic width is the same.
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They took the same breath in.
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That turned out to be ground glass.
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It was biopsied, and it was DIP,
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desquamative interstitial pneumonitis.
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A patient who's got extrinsic allergic
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alveolitis, look at the 10th rib,
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that's where the diaphragm is.
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These intrathoracic widths are exactly the same.
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After the treatment, when the compliance
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of the lungs returned to normal, the
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diaphragm descended to a lower level.
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Now we'll kind of apply it here.
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A 49-year-old got a CTA.
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This is what I'm talking about.
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You'll notice the posterior
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wall is sort of straightened.
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So it's sort of like mid-expiration.
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There is a dark bronchi sign.
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Is this ground glass?
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Is this expiration?
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Um, hmm.
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Well, shoot, that's hard.
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What's one of the clues?
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Does it get brighter as you go down?
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No, it doesn't, does it?
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This is relatively uniform.
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So in your report, you would favor that this
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is a ground glass process because there's
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not that increasing density as you go down.
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This patient did get a 76% of
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predicted and they turned out that they
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had basically hypersensitivity and
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pneumonitis with some cellular NSIP.
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So that was real ground glass.
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It can be tricky and it can be tough.
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So, last one, underexposed, large
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patients, or pleural effusions.
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This is an abnormality that's
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outside the lung that can cause an
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opacification and can mimic ground glass.
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The key here is to look at the vessels.
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These vessels are sharp.
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That means that there is air around them.
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Therefore, the opacification
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is probably outside the lung.
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In this case, it's pretty evident
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because you can see that pleural effusion,
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but that pleural effusion wraps around.
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So if you have an increased area of
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opacification, can you see the vessels sharply?
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Yes.
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Let's think that this is a mimic and it's
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something outside the lung, like pleural fluid
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or an underexposed exam.
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So the mimics, they still occur.
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You're going to encounter them.
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It can be confusing sometimes to tell if this
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is a ground glass process or normal lungs.
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Look at the increasing density of the
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density and look for the intrathoracic width.
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Is it the same?
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If you're not sure, consider doing a CT scan
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of full inspiration or referral for a diffusing
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PFT measurement because that's pretty helpful.
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If it's normal, it was probably just normal lung.
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And as always, don't say
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poor inspiratory effort.
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With that, I thank you very much.
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