Hey this is Rishi and today we're going to be talking about subsolid nodules, what they
are and why we treat them differently from solid nodules.
So first it's important to remember what a nodule is.
This is from the Fleischner Glossary.
A nodule is just a round or irregular opacity that measures less than 3 cm.
When we see nodules on CT, we often look at multiple characteristics like the size, shape,
and borders.
Another important characteristic is the attenuation.
In other words, is the nodule solid or is it subsolid.
A solid nodule is one in which the underlying lung parenchyma is completely obscured, like
this nodule right here.
A subsolid nodule can be of two kinds.
One kind is completely groundglass in which the whole nodule is groundglass in attenuation
and it does not obscure the underlying lung architecture.
The other is part solid in which some of the lesion obscures the underlying lung parenchyma,
but there's also a groundglass component that does not obscure the lung parenchyma.
So when you have a subsolid nodule, it's important to say whether it's completely groundglass
or whether it's part solid.
The reason why we treat solid nodules differently from subsolid nodules is that subsolid nodules
are more likely to be lung cancer compared to solid nodules.
So if you had 100 subsolid nodules and 100 subsolid nodules, you're going to have more
lung cancers in the group of subsolid nodules.
Now on the other hand, solid lung cancers are more aggressive than subsolid lung cancers.
Let's look at that a little bit more closely.
This is an important article that came out of the Journal of Thoracic Oncology in 2011
in which Lung Adenocarcinomas were reclassified.
Prior to this, the term bronchoalveolar carcinoma (BAC) was used for multiple entities including
adenocarcinoma in situ, minimally invasive adenocarcinoma, lepidic predominant adenocarcinoma,
and so on.
Now, for the purposes of this talk, I'd like to draw your attention to a few entities.
Atypical adenomatous hyperplasia, which is a pre-cancerous condition, adenocarcinoma
in situ which is cancer, but is preinvasive, minimally invasive adenocarcinoma, and lepidic
predominant invasive adenocarcinoma.
The reason why we're focusing on these tumors is that these are the tumors that are likely
to be subsolid in attenuation.
From a radiologic perspective, it's helpful to think about these entities as existing
along a spectrum of increasing invasiveness and malignant potential.
So atypical adenomatous hyperplasia will have epithelial proliferation, but it's going to
have mild to moderate atypia as compared to adenocarcinoma in situ which will have moderate
to severe atypia.
There's multiple different things a pathologist will look at to differntiate these entities
like cellular crowding and density, the presence or absence of coarse chromatin and so-on.
For adenocarcinoma in situ, this is considered cancer, but as the in situ component suggests,
the cells are still growing in a lepidic pattern.
In other words, they are growing along the alveolar walls and respiratory bronchioles,
and not invading the stroma.
Now, that's different from minimally invasive adenocarcinoma in which there is an invasive
component that is seen pathologically.
It is called minimally invasive because that invasive component is by definition less than
or equal to 5 mm in size.
Now, when we're talking about invasive adenocarcinomas, there are multiple different subtypes.
The subtype that I'm interested in for this talk is the lepidic predominant invasive adenocarcinoma.
That differs from minimally invasive adenocarcinoma in that the invasive component in this entity
is greater than 5 mm whereas the invasive component in this entity is less than or equal
to 5 mm.
Now from a radiologic perspective, as you go from left to right along this spectrum,
the lesions increase in size and density.
So, for a lesion that is 5 mm or less and pure groundglass, that is more likely to be
atypical adenomatous hyperplasia and as you increase in size and the solid component,
that's more likely to be minimally invasive adenocarcinoma or invasive adenocarcinoma.
For lepidic predominant invasive adenocarcinoma, depending on how much of an invasive component
you have, you can have a lesion that is mostly or completely solid.
But in general, the increasing size of the solid component means that you have an increasing
chance of having invasiveness.
So if I were dictating a case with multiple subsolid lesions, I would list as the impression
as number 1 the lesion with the largest solid component because in my mind, that is the
most suspicious lesion with the highest potential of being invasive.
So for this lesion which is a pure groundglass nodule, I would give a differential at the
first timepoint of infection or inflammation, atypical adenomatous hyperplasia, or adenocarcinoma,
likely in situ.
Usually instead of saying adenocarcinoma in situ, I give the term low grade adenocarcinoma.
If we get a follow up and that lesion is still there, it is not likely at that point to be
infection or inflammation, but it could be focal fibrosis.
So I would add that to the differential, take out infection or inflammation, but I would
still keep atypical adenomatous hyperplasia and adenocarcinoma.
Now what about a lesion that is part solid?
For the first timepoint, I would still include infection or inflammation, I would move adenocarcinoma
to number 2, and in this case, it is likely minimally invasive, but I usually don't say
that.
And then 3 I would put atypical adenomatous hyperplasia.
I would still include atypical adenomatous hyperplasia because this solid component may
not indicate an invasive component all the time.
It could represent a little area of mucus plugging or atelectasis, so that's why I still
include atypical adenomatous hyperplasia.
At the second timepoint, I take out infection/inflammation, put in focal fibrosis, and I would still keep
adenocarcinoma and atypical adenomatous hyperplasia.
Now when you measure these lesions, it is important to measure both the entire lesion
and the solid component.
And that's because in the TNM staging criteria the T component, the tumor size is based on
the solid part of the lesion, not the entire lesion.
So in this example, the solid part of this lesion is 15 mm which would make it a T1b,
and not 25 mm which would make it a T1c.
There's a few other features that would increasing my suspicion that I'm dealing with cancer.
One is whether there is tenting of the fissure.
You can see there's a little bit of deflection of the fissure, but that's easier to see on
the sagittal images.
So if you're deciding if there is tenting of the fissure, look at the sagittal images
to help you.
The presence of spiculated margins makes it more suspicious for cancer, and the presence
of air bronchograms makes it more suspicious for cancer.
So when we're talking about management, there's a lot of considerations that go into how to
manage these lesions.
These are just a few.
So size and growth are probably two of the most important.
The presence or absence and size of the solid component which remember that tells you the
likelihood of having an invasive component.
The other suspicious characteristics, tenting of the fissure, air bronchograms, and spiculated
borders.
The presence of other nodules.
Patient age and comorbidities.
And then whether it is a screening or incidental finding.
For lung cancer screening, Lung-RADS has management recommendations for part solid nodules and
for ground glass nodules.
Take a look at the management recommendation for groundglass nodules measuring up to 30
mm.
It says that these are to be followed with low dose CT in 12 months.
The reason we can do that is that these cancers tend to have a very slow growth rate compared
to solid cancers, so it is ok in some cases to follow it in 12 month intervals.
For incidentally detected lesions, there are recommendations from the 2017 Fleischner Society
guidelines.
It is important to remember that these recommendations don't apply to lung cancer screening, patients
with immunosuppression, or patients with known primary lung cancer.
Also these recommendations are for patients who are 35 years and older.
It is important to remember that these are just recommendations and the management of
these lesions should be individualized to the patient based on a host of factors including
the patients preferences.
So deciding whether to just follow the lesion radiographically, biopsy, radiate, or resect
should be done on a case-by-case basis.
OK, that's all I have for this video.
Here are some references which I'll link in the description below.
If you have any questions, please leave them in the comments below.