Hey, everybody, this is Rishi Agrawal, and in this video,
I'm going to be talking about interstitial lung disease.
This is going to be the first video in a series about interstitial lung disease.
And this video is going to be about how to organize your findings.
So this is the roadmap that I want to go through.
First, we're going to talk about the distribution of disease.
And when we talk about distribution
in interstitial lung disease, there's two ways we can classify that.
The first is
in the cranial caudal dimension and the second is in the axial dimension.
Then we're going to talk about specific findings that I include in my report.
And then the third is we're going to talk about this idea of a pattern
versus diagnosis.
So whenever I approach a case of interstitial lung
disease for the first time, it's kind of like a game of guess who?
And guess who, if you remember was this game where there's two players
and each player gets a card with someone's face on it.
And by asking simple questions like, Does your player have a hat?
Does your player have brown hair? Yes or no?
You can start to exclude things and include things,
and by a process of elimination, you get to the correct answer.
One of the best ways to start that process of elimination
is to figure out the cranial caudal distribution.
And you can even do this on a chest x ray if there's sufficient disease.
And the two distributions are mid to upper lung
predominant or lower lung predominant.
Now, on a normal chest x ray,
the hila bisect the chest so that there's an equal amount of lung
above the hila, as there is below the hila. OK.
So in this example, I drew a horizontal line
bisecting the hila and you can see it's about equal above and below.
In this case,
if we bisect the hila, there's a lot more lung
below that line compared to above that line,
which means that this person has upper lung predominant disease.
So I can use my differential for upper lung predominant disease -- SHORTI.
Sarcoid, HP, occupational, radiation, TB/fungus
and IPPFE, or idiopathic pleuroparenchymal fibroelastosis.
And even more importantly, we can exclude a couple of things
like usual interstitial pneumonia and nonspecific interstitial pneumonia.
Let's take a look at some of those things in the differential.
In a patient with fibrotic sarcoid,
you'll see bundles of traction bronchiectasis
that have a mid to upper lung predominance and usually a central distribution.
In a patient with chronic hypersensitivity pneumonitis,
you'll see fibrosis in a heterogeneous distribution
and you'll see air trapping on your expiratory images.
Now these other three things in the differential, usually,
the patient will have a history of old TB or a history
of occupational lung disease or exposures or cancer with prior radiation.
Well, how about lower lung predominant disease?
So if you take a look at this chest X-ray and we draw a line by bisecting the hila,
you can see that
there's a lot more lung above that line compared to below that line.
So the hila are being retracted inferiorly,
and this is a patient with lower lung disease.
So my main two things in the differential
are going to be UIP and NSIP.
HP I included in my upper lung predominant differential.
But I would still include it in my lower lung predominant differential, too,
because a significant number of patients
with HP will present with lower lung disease.
I would also exclude the occupational lung
diseases like silicosis or berylliosis,
and I would exclude fibrosis
due to TB and fungus and IPPFE.
Now, in
practice, when we're talking about lower lung predominant disease,
the main two things that I'm thinking about are NSIP and UIP.
There are other things in the differential like DIP, but that's going to be rare.
And most patients with DIP have a history of smoking.
Also, you can think about cystic lung diseases like lymphocytic interstitial
pneumonia (LIP), but that's going to look very different from these two entities.
OK, so that's cranial caudal distribution.
The second type of distribution is the axial distribution,
and it's very helpful if the axial distribution looks like this
where you have a lot of the disease in the central or peribronchial portion
of the lung and you have sub pleural sparing in the periphery of the lung.
Because in this case, you can exclude UIP.
I would include things like sarcoid,
NSIP, HP and organizing pneumonia.
Now the reverse is not as helpful.
So if you have a patient with predominant disease in the periphery
or in the subpleural part of the lung, then
I would include things like UIP,
NSIP, HP and organizing pneumonia.
And I wouldn't necessarily exclude things just based on that distribution.
For example, if you had a patient with peripheral predominant
ground glass opacity or consolidation, then you couldn't really exclude
NSIP or organizing pneumonia.
Now, once you figured out the distribution,
the next step is to describe the findings.
And to describe the findings, you have to use the proper terms.
So I highly recommend that you read this article
if you haven't already, it's the glossary of terms for thoracic imaging
that was put out by the Fleischner Society.
And the four main terms that I always
talk about in patients with interstitial lung disease
are reticulation, ground glass, opacity,
honeycombing, and traction bronchiectasis.
And I usually talk about whether they're present or absent.
So even if they're not there, I'll say that there's no significant
ground glass opacity or there's no significant honeycombing.
Now I did a whole video about these four terms,
so I recommend that you watch that if you haven't already.
Finally, one important concept to remember
about these interstitial pneumonias
is that the pattern that you see on
imaging is not the clinical diagnosis.
So, for example, if you call a patient a UIP pattern,
most of those patients will have idiopathic pulmonary fibrosis.
But a minority of patients can have rheumatoid
or systemic sclerosis or hypersensitivity pneumonitis, et cetera.
Similarly, if you call
a case NSIP, then NSIP is not the diagnosis.
The patient could have idiopathic NSIP, which is not super common.
Most of the time, it's due to a connective tissue disease or a drug reaction.
And the same is true for organizing pneumonia.
You can have idiopathic organizing pneumonia, which is called
cryptogenic organizing pneumonia, but a lot of patients will also be due
to infection or drug toxicity or connective tissue disease.
The point I'm trying to make is that these idiopathic interstitial pneumonias
are not the diagnosis in the in and of themselves,
they're the radiologic or histologic pattern.
And you have to pair that with the clinical history
to come up with a clinical diagnosis.
All right.
So in this video, we talked about how to organize your findings
by determining the cranial caudal
and axial distribution of disease
and by using the correct terminology
in future videos, I'm going to be talking about specific radiologic patterns.
If you have any questions, please let me know in the comments below.
Thanks.