Hey, everybody, It's Rishi Agrawal, and in this video, I'm going to show you
another classic case.
This case started with this chest x ray, and I'm going to give you a second
to make the finding.
It's right here.
If you look in the right upper lung superimposed over
the second rib, is this nodule.
I can't really see it on the lateral view.
It would be in this general area right here.
But there's nothing really that I can point out on the lateral view.
A CT was ordered for further characterization
and it showed this well circumscribed nodule in the right upper lobe.
It's about 12 mm in size,
and if you look at the bronchovascular
bundle that leads to that main nodule,
it's studded with multiple smaller nodules.
And if you look
at another adjacent bronchovascular bundle,
that too is studded with a few small nodules.
When we look at the soft tissue windows, it looks like there's a little
bit of fullness in the right hilum, but it's difficult to differentiate
a lymph node from a vessel because we don't have contrast.
So this appearance is a classic
granuloma specifically, this is from histoplasmosis.
The reason why I want to show you this case is
because the radiologist has a big role to play in cases like this.
If you were familiar with the morphology,
with this well circumscribed central nodule
and smaller nodules in a peribronchovascular distribution,
then you can make a confident call of a granuloma,
and save the patient time, money, heartache, and morbidity
by steering the management towards a follow up chest CT
rather than a PET/CT, a biopsy, or surgery.
And even if you were a little worried about it,
you could do the initial follow up study in 1 to 2 months
and then do another in about 6 months and then another in 12 months.
Histoplasma
capsulatum is a common endemic fungal infection.
If you remember that term from med school, endemic infection refers to an infection
that happens commonly, but it's confined to certain areas of the world or country.
This is the first map of histoplasma prevalence in the United States,
and it was published in 1969 when some researchers performed skin
testing for histoplasma among new naval recruits
and then traced them back to their specific county of origin.
And it showed a large concentration of histoplasma
here in the Midwest of the United States and a much lower prevalence elsewhere.
These areas here in California were thought to be due
to cross-reactivity to another fungal infection.
Today, because of a number of reasons,
the map of the United States probably looks something like this
where the eastern United States has a high concentration of histoplasma
and the western has a lower concentration.
That's not to imply that the western United States has no cases,
but the numbers are just lower compared to the eastern U.S.
Here's a world map that was based on a literature search published
in the journal Micropathologia in 2020.
It's important to remember that histoplasmosis can be found worldwide,
so the highest numbers are going to be found in the places that are green.
But sporadic cases can occur even in these darker areas.
In endemic areas, histo is found in the soil and it's in
particularly high concentrations in soil that has a lot of bird or bat droppings.
So that's why a classic test question
is that you have a patient who goes spelunking and catches histo.
But you don't really have to live in rural areas or near caves to get it.
Even in urban areas like under trees or where a lot of birds hang out or
during construction or cleanup of an area, it's possible to be exposed to histo.
If you're looking at
soil containing histo under the microscope,
you're going to find fungal hyphae as well as these things
called microconidia and macroconidia.
Another name for these conidia are spores.
And when the dirt or soil gets stirred up,
these spores are released into the air and breathed in by the patient.
In the lungs, the fungus can cause a pneumonia.
But in most patients, like over 99%,
they have no symptoms or very minimal symptoms.
And so most patients
don't even seek medical care, and imaging is not usually obtained.
It's only later, after the body fights off the infection
that the remnants of the infection are found in the form of a granuloma.
And if that granuloma hasn't had time to calcify,
then you're left with something like this.
In adults,
it can take a long time for the nodule to calcify.
Like in this patient, it took three years to get to this point
where the lesion measured 100 HU.
And you can see with the naked eye some faint calcification.
But if you put an ROI over it, you can see that even in two years
it went from 25 HU to 60 HU
indicating some low level calcification.
The lymph nodes will also calcify.
This is the CT that was done 4 years after the initial.
And you can see there's a peribronchial lymph node that's calcified
and that initial hilar lymph
node that we were concerned about has calcified.
Now, I mentioned earlier that most patients have either
no symptoms or very mild symptoms.
Some patients can have moderate to severe pulmonary illness.
And that can happen if the patient is immunocompromised
with like HIV/AIDS or pharmacological immunosuppression,
or it can happen if the patient inhales a large inoculum of the spores.
This is a patient that presented with cough and dyspnea.
And I want to show you the natural history of the granuloma formation.
Here's a patient who had right lower lobe ground glass, opacity
and in the center of that ground glass opacity,
there's a more focal oval consolidation, which on soft tissue
windows has a low area of density centrally, indicating necrosis.
When we go up to the mediastinum,
you'll see enlarged lymph nodes
in the subcarinal region and in the right hilum.
Four months after the initial CT,
you'll see that the ground glass opacity has went away and we're left with this
central nodule, which has become much smaller
in size on soft tissue windows.
The nodule isn't yet calcified and has a mean HU of about 35.
11 months after the initial CT, the nodule is more
well circumscribed, but not really changed in size or density.
Two and a half years after the initial study,
the nodule is about the same size as it was before.
But if we look at the soft tissue windows, you can see some faint laminar
calcification, kind of like a jawbreaker candy.
This is ten years after the initial study, and you can see that
the nodule has decreased in size
and on soft tissue windows, that laminated appearance of calcification
has become even more pronounced with dense calcification
around the periphery and in the middle of the lesion.
Here's another example.
We have a solid, very well circumscribed, dominant nodule surrounded
by multiple smaller nodules
that seem to abut the bronchovascular bundle.
Occasionally these can be confused for arteriovenous malformations
because the nodules abut the vessels
that lead into the main lesion.
That's not to be confused with a tortuous dilated vessel.
It's just that there's nodular studding of the vessels leading to the lesion.
Here's one with obvious calcification.
We have this central dominant nodule that's well circumscribed
and multiple surrounding satellite nodules
and a bronchovascular distribution.
And then we have calcification of that ipsilateral lymph node.
When the patient is first infected,
the organism is taken up by macrophages, but it isn't killed.
And that's how it can enter
the bloodstream, where it can be deposited in the spleen and liver.
Those granulomas in the spleen can eventually calcify.
And that's why patients with histo often have
calcified splenic granulomas, like this patient.
Here's one last example.
So here's a patient with a central dominant nodule
and a couple surrounding satellite nodules.
But what you'll notice is that this dominant nodule is not well circumscribed.
Instead, it has spiculated borders.
And on the coronals you can see that spiculation very well.
So this patient is not a granuloma
because the central nodule is not well circumscribed, it's spiculated.
This patient is going to
require a PET/CT and thoracic surgery consultation.
And this patient turned out to be lung cancer.
Okay.
In summary, if you have a solid, well circumscribed nodule
and surrounding smaller nodules in a peribronchovascular distribution,
this is a very good sign of a granuloma, specifically histoplasmosis.
So if you live in an endemic area and you see these features,
then I would recommend doing a follow up CT in 1 to 3 months,
depending on the size of the lesion and how typical the features are.
After that first follow up,
you can lengthen the time interval for the follow up scans.
If you recommend a PET/CT,
the lesion and the lymph nodes are going to be hot on PET,
which might persuade someone to biopsy or even remove it.
So i think it's better to just follow it with a regular non contrast chest CT.
If you have any questions about this topic or any other chest radiology topic,
let me know in the comments below. Thanks.