Hey, everybody, it's Rishi, and in this video,
I'm going to show you a classic case.
You've already probably seen the title of this video,
but let's take the case as if we don't know what the diagnosis is.
Let's start out with a lung windows.
As I scroll through the lung windows,
you can see that the right lung is pretty much normal.
But the left lung is abnormal.
First of all, it's small.
There is volume loss in the left lung.
And you can see that there's a lot of bands of atelectasis in the left lung.
And you could see that the mediastinum is shifted towards the left.
The second thing is that there's multiple lines in the left lung.
And if we look closely, those lines represent interlobular septations.
So we have interlobular septal thickening here.
Most of the time when you see
interlobular septal thickening, you're dealing with pulmonary edema.
But why is the pulmonary edema in this case so unilateral
where it only affects the left lung and not the right lung?
So I can think of a few different causes.
And this is not a comprehensive list, but it covers many common
causes of unilateral pulmonary edema.
One is after a thoracentesis.
So if a patient has had a long
standing pleural effusion and you tap that pleural fluid,
then the expansion of the lung can cause unilateral pulmonary edema.
Another cause is lymphangitic carcinomatosis.
So when tumor cells block the lymphatic channels of the lung,
then you can get unilateral pulmonary edema.
A third cause is mitral regurgitation.
So when you have mitral regurgitation, that regurgitant jet of blood
can be directed selectively into one of the pulmonary
veins, causing unilateral or focal pulmonary edema.
And the classic example is in the right upper lobe, and you'll frequently
see that on tests.
And then finally, pulmonary vein stenosis can cause unilateral pulmonary edema.
You can have pulmonary venous stenosis
from external compression, from a mass or lymph nodes.
And you can have it from internal stenosis,
like in a patient who's had pulmonary vein isolation for atrial fibrillation.
So let's take a look at the mediastinum in this case to see what we find.
Here we have the soft tissue windows of the patient.
And if I narrow the windows here, you could see that there's
this calcified lesion in the left hilum.
And if I scroll down, you can see that
the right inferior and superior pulmonary veins are patent.
But the left inferior and superior pulmonary veins are occluded.
So that's why this patient has unilateral pulmonary edema.
So what could this be?
The two main things I would be thinking about in this patient
are some kind of malignancy and fibrosing mediastinitis.
The presence of that
calcification is a good sign that this is fibrosing mediastinitis.
But I would still want a biopsy, because sometimes you can have tumors
that engulf calcified lymph nodes and it can look like this.
Fibrosing mediastinitis can be divided into two causes,
granulomatous causes and non granulomatous causes.
Most of the time it's due to granulomatous causes.
And where I live in the Midwest
of the United States, it's mostly due to histoplasma.
But if you live in another part of the world, then perhaps TB
is more common in your area than histoplasma.
You can also have it with other fungal infections and sarcoid.
The non-granulomatous causes include radiation therapy
and autoimmune diseases like lupus and rheumatoid arthritis.
You can also see it with IgG4 disease.
In most patients with a histoplasma infection, they get a calcified granuloma
in the lung and then calcified mediastinal and hilar lymph nodes.
But for some reason, in these patients, they have this progressive
inflammatory reaction that causes soft tissue to form.
And the characteristic finding for these patients with fibrosing mediastinitis
is that soft tissue occludes vessels and sometimes even bronchi.
In my experience, most of the time it's the pulmonary veins
and the SVC that are affected by fibrosing mediastinitis.
But sometimes you can have pulmonary
arterial occlusion and even bronchial occlusion.
Let's take a look at another case.
So this is this is another patient with fibrosing mediastinitis.
And as we go to the upper part of the chest, you can see
that the contrast was administered in the left upper extremity.
And there's dense opacification of multiple collateral vessels
around the spine.
And as we go down, you can see that the azygous vein
and the hemiazygous vein are densely opacified, with contrast.
The IVC also has a lot of contrast in it.
Now, if we go up and we look at the SVC, so this is the left brachiocephalic vein.
This is the right brachiocephalic vein.
Then I'm scrolling down now.
You can see that contrast
comes to like this thread like focus right here.
And most of the SVC is occluded there
secondary to this soft tissue lesion in the right paratracheal region.
And if I narrow the windows here, you can see that that soft
tissue lesion has this coarse central calcification in it.
This patient, if we look at the pulmonary veins,
the pulmonary veins are completely normal.
So this patient's pulmonary veins are normal, but
their SVC is almost completely occluded.
If you want to know more about fibrosing mediastinitis,
there was a really good RadioGraphics article in 2019, which I'll link to below.
Anyway, if you have any questions, let me know in the comments below. Thanks.