Hey, everybody, it's
Rishi Agrawal, and in this video, I want to show you a classic case.
We're going to start out with a chest x ray in this patient.
This is the current chest x ray
and this is the prior chest x ray from about two years ago.
The history is it's a 65 year old man with asthma.
There's a couple of abnormalities that I want to point out
on the current chest x ray.
One is that there's an area of reticulation here in the right upper lung.
And the second is that there's this elongated opacity in the left lower lung.
You can see on the comparison
that that area of reticulation was present two years ago.
However, the elongated opacity was not there.
Let's zoom in a little bit on this reticular area.
With this area enlarged
I think you can better appreciate that this area of reticulation
should probably be better characterized as bronchiectasis.
We have a bronchus right here that appears dilated.
And we also have a bronchus that goes out in this direction here.
This is the lucent area, and this is the superior wall of the bronchus.
This is the inferior wall of the bronchus.
Let's take a look at the lateral view.
On the lateral view,
you can see that area of reticulation right here in the upper lung.
And you can see the elongated opacity here behind the heart.
So at this point, we know that the patient has asthma.
We think they probably have bronchiectasis.
And given this elongated opacity, this is probably an area of mucus plugging.
Because I know the patient has asthma.
One of the top things in my differential would be ABPA
which stands for allergic bronchopulmonary aspergillosis.
In a patient with a new mucus plug.
I would also want to include tumors in my differential.
For example, carcinoid can obstruct a bronchus and cause distal mucus plugging.
You could also have more aggressive tumors like adenocarcinoma or squamous cell
carcinoma that cause distal mucus plugging.
And then perhaps this isn't even a mucus plug at all.
I would also include things like bronchopneumonia in the differential.
I would want to get a CT at this point to further investigate.
This chest CT was done a couple of days after the chest
x ray, so let's just scroll through and see what we can find.
So that
area of reticulation that we suspected was bronchiectasis is indeed bronchiectasis,
which you can see here in the right upper lobe.
One thing to note about this bronchiectasis is that it's in the middle
part of the lung, meaning it's not in the lung periphery
and it's not all the way towards the hilum.
Let's keep going and see what we see.
OK, so there's more bronchiectasis here
in the superior segment of the right lower lobe.
And then we come to the elongated opacity that we saw on the chest x ray.
So on the CT, it turns out to be this branching structure
that correlates with a dilated bronchus.
And on the soft tissue windows we have an important clue here,
which is that the internal attenuation of the mucus plugging is dense.
In fact, it's even denser than the skeletal muscle.
So if I put a Hounsfield unit on it,
it's 97 Hounsfield
units compared to skeletal muscle,
which is only 42 Hounsfield units.
So this I would call high attenuation, mucus plugging.
If we continue to scroll distally you can see
that there are some areas of tree-in-bud opacity down here
in the left lower lobe distal to that central mucus plug.
And then we have a little bit of ground glass opacity
around some of those areas of tree-in-bud.
So putting everything together, we have a patient with asthma,
bronchiectasis, high attenuation mucus plugging,
tree-in-bud opacity and a little bit of ground glass opacity.
So all of these findings are consistent with ABPA.
ABPA is a disease in which the airways are colonized with Aspergillus.
And it happens almost exclusively in patients with asthma or cystic fibrosis.
Now, the fungus doesn't invade the mucosa, but the patients have this IgE
and IgG mediated immune response that causes inflammation
that likely leads to airway damage and bronchiectasis.
Most patients have symptoms of asthma and recurrent exacerbations.
And then patients may even sometimes expectorate these brown mucus plugs
on chest x ray.
The classic chest x-ray finding is this, which is a "finger in glove" opacity,
which represents a mucus plug within a dilated airway.
On CT, you'll see bronchiectasis in most patients,
although a minority of patients (about 1/5) won't have any bronchiectasis.
This finding of high attenuation, mucus plugging,
is very specific for ABPA.
In fact, this article from 2013 describes
this sign as being 100% specific.
It's thought that the high attenuation mucus plugging on CT
is due to calcium salts and metals
or possibly desiccated mucus.
This is a really important sign in patients with cystic fibrosis
because in patients with cystic fibrosis, they'll have bronchiectasis
that's very similar to other patients with ABPA.
So the presence of the mucus plugging tells
you that that patient not only has CF, but also has ABPA.
On top of that, you can also see signs of small airways
disease in patients with ABPA like mosaic attenuation
and tree-in-bud opacity like we have in this patient.
And then if the patient has post obstructive disease like post
obstructive pneumonitis, you can see ground glass attenuation or consolidation.
All right. That's it for this video.
If you have any questions
about the radiology of ABPA, let me know in the comments below.
Thanks.