Hey, everybody, it's Rishi Agrawal.
In this video, I'm continuing the series on TNM staging of lung cancer.
Specifically, we're going to talk about the T category, which is tumor.
There are two components of the T category.
The first is size.
The bigger the tumor, the higher the T category.
The second is location.
So if the tumor invades specific structures, it can be upgraded
to a higher T category, even if it's a smaller tumor.
We know from the IASLC database that each cm increase in tumor size
from less than 1 to 5 cm was associated with a worse prognosis.
Here's the survival curves for tumors
going from one cm to over seven cm.
You can see that these curves are separated very well without overlap,
meaning that the size increase has a real world impact on survival.
So the 8th edition of TNM
made each 1 cm increase from 1
to 5, a separate T category,
which is a lot easier to remember compared to the old 7th edition.
The way I drew these numbers, a 3 cm nodule is a T1c,
but a 3.1 cm nodule would be T2a.
So T1 encompasses lesions up to 30 mm.
T2 goes from 31 to 50
and T3 goes from 51 to 70.
Then T4 is 71 millimeters and above.
It's important to know the correct way to measure a tumor.
In the case of TNM, the tumor size is based on the single longest axis.
That's different from lung cancer screening
because according to the lungRADS criteria, nodule size is
based on the mean of the lung axis and the orthogonal axis.
It doesn't make too much of a difference for most cases, but it can make
a difference, particularly in cases when the nodule is oblong in shape.
Next, you want to use all your views.
You're not limited to using just the axial images.
If the tumor is greatest in the sagittal dimension, that's what you should use.
So in this example, this tumor was 18 mm in greatest axial dimension. But
on the sagittal images, it's 23
mm which would bump it up from a T1b to a T1c.
It's also
important to use lung recons and lung windows.
If you're measuring the tumor on soft tissue windows, there's a chance
that you could underestimate the tumor
size, particularly if the lesion has spiculated borders.
In this example, you can see that the soft tissue windows
underestimate the actual size of the tumor.
Finally, when you have a lesion that's part ground glass and part solid,
the T category is based on the solid component, not the entire lesion.
But in general, it's a good idea to report
both the solid component and the entire lesion.
Let me show you an example.
Here's a subsolid lesion that I measured on the sagittal recon.
If we take the greatest dimension, this is 14 mm.
So that would make it a T1b.
But of course, we just want the solid part for the T category.
So in this case, the solid part is only 8
mm, which would make this a T1a.
The other reason why you should measure the solid component
is because the solid component
tends to be the part of the lesion that grows the fastest.
On pathology, the solid component correlates with invasive tumor
compared to the ground glass part, which is usually lepidic growth.
So if you have two time points and you just measure the ground
glass component, you can fool yourself into thinking that the lesion is stable.
In this case, comparing the baseline to the 6 month
follow up, the maximum diameter is the same.
But if you look at the solid component, it grew from 5
mm to 8 mm.
All right.
The second criteria for the T category is location.
Remember that the location of a lesion can only upgrade the T category.
For example, it can take it from a T2 to a T3, but not the other way around.
All right, let's start with T1.
T1 lesions are tumors that are 3 cm or less,
and the tumor is surrounded by lung or visceral pleura
without evidence of invasion of a main bronchus.
It can invade a lobar bronchus, but it can't go more central than that.
So here's an example of a T1 lesion.
This is an 11 mm nodule that is surrounded by lung tissue.
Here's another example.
This is an 8 mm lesion, which makes it a T1b and it touches the pleura.
So if it simply touches the pleura,from a radiology standpoint,
you can't be sure whether or not it invades the pleura.
To be sure, this lesion needs to be resected and visceral
pleural invasion needs to be evaluated by a pathologist.
There are some instances
where you can say there is plural invasion and I'll show you those in a second.
a T2 lesion by size is between 3.1 and 5 cm.
By location, it's a tumor that causes atelectasis
or pneumonitis of a part of a lobe, the whole lobe, or the entire lung,
or it's a lesion that invades the main bronchus or visceral pleura.
In this example, there's a 39 mm mass at the right apex
that abuts the plural surface.
It again just touches the pleura.
And we can't say for sure whether there's plural invasion.
But take a look at this example.
Here's a 28 mm nodule which would make it a T1c,
and it abuts the visceral pleura, the major fissure.
But if we look at the sagittal images and zoom in, what you see
is on the other side of the fissure, there's this spiculated border.
So if you see either a spiculated border or a lobular border
on the other side of the fissure, that's a really good sign that
the tumor has spread across the fissure and therefore has invaded
the visceral pleura which bumps it up to a T2.
If this nodule only touched the fissure and even if it caused a little bit
of displacement of the fissure, but it was smooth on the other side,
that's not enough evidence for me to say that the nodule crossed the fissure.
There has to be spiculation or lobulation on the other side for me to say
that this is visceral pleural invasion with a high degree of confidence.
In this
example, we have a nodule in the perihilar right upper lobe
that measures 26 mm which makes it a T1c.
But if we scroll up a bit, we can see that the tumor causes atelectasis
of the anterior segment of the right upper lobe, which makes this a T2.
For T3, the size criteria are 5.1 to 7 cm.
And here's the other criteria.
A separate nodule in the same lobe bumps it up to a T3.
Invasion of the parietal pleura chest wall, phrenic nerve
and parietal pericardium also take it to a T3.
So here's a lesion in the left lower lobe, it's
54 mm and surrounded by lung.
And this is a T3 purely by size criteria.
Here's another example.
So there's a mass in the right upper lobe, it measures
47 mm which makes it a T2b.
But if we scroll down a little bit, there's another nodule in the right
upper lobe.
So we have a separate nodule in the same lobe.
So that bumps this case up to a T3.
Now I'd
like to mention at this point that the 8th edition of TNM
has a discussion about lung cancers with multiple lesions.
So in the case of a separate nodule in the same lobe,
we're talking about an intrapulmonary metastasis.
These are additional nodules in the lung
with the same histopathological type as the primary lesion.
There are separate rules for patients who have second primary tumors,
multifocal ground glass adenocarcinoma and diffuse pneumonic type adenocarcinoma.
Now, I'm not going to delve into each of these special cases
in this video, and I'll save that for another time.
But it's important to know that these other categories
have special rules for TNM Staging.
Okay, let's take a look at another example.
Here's a right upper lobe mass measuring 47 mm
making it a T2b by size criteria.
It abuts the plural surface, but when we go to the soft tissue windows,
you can see that this tumor goes all the way up to the rib
and there's even soft tissue between the ribs.
So when you see this appearance, this is a good indication that there's
chest wall invasion.
Compare that
to another case where the tumor abuts the costal pleura.
In this example, there's preservation of this layer of fat that separates
the ribs and the intercostal muscles from the tumor itself.
So in this case, it's not possible for me to say whether there's chest wall
invasion or not, and it's best left up to the pathologist.
Here's a different case with a left upper lobe mass.
It's 44 mm and it abuts the mediastinal pleura.
If we go to the chest x-ray, you can see that there's elevation of the left
hemidiaphragm, which is a good indicator that there's phrenic
nerve invasion.
Let's move on to T4.
One of the criteria that makes it a T4 lesion
is when there is a separate nodule in a different lobe of the same lung.
Another criteria is invasion of the mediastinum, including any of these
mediastinal structures, invasion of the diaphragm, and the spine.
Here's a lesion that's T4.
It's 10 cm in size and it has a broad base with the mediastinum.
Here's another T4 lesion.
There's a relatively small primary tumor in the right
upper lobe that's 4.1 cm, making it a T2b,
but there's a separate nodule in the right lower lobe that bumps this up to a T4.
By the way, having a separate nodule in the contralateral lung
would change the M category.
That would make it an M1a.
Here's another example.
So we have a patient with a 5.8 cm left upper lobe mass.
And if you go to the soft tissue windows, you could see that the mass invades
the mediastinal fat next to the aortic arch and soft tissue goes all the way
up to the descending aorta, making this a T4.
Here's another lesion.
It's a 10 cm Pancoast tumor of the left apex.
So it's already T4 by size criteria.
But there's also erosion of the T3 vertebral body here.
So spinal erosion makes this a T4 as well.
Okay, finally, I just want
to cover for a second special T categories.
Tx is a situation where the primary tumor cannot be assessed.
This may be a case where you don't have imaging for some reason,
but you have evidence of lung cancer, like on a sputum or bronchial washings.
T0 is a situation that you might run into occasionally.
It's when you don't have evidence of a primary tumor,
but there are metastases on path that look like they're coming from the lung.
So one good example
that you can see from time to time is when a patient has plural metastases.
So nodules in the pleura which on path seem to originate from a lung primary,
but you can't find a primary tumor in the lung that you would give it a T0.
These other two categories are more common.
Tis and T1mi.
Tis is carcinoma in situ
and T1mi is minimally invasive adenocarcinoma.
Both of these are pathologic criteria,
not something that we can diagnose by imaging,
but on imaging the Tis tumors tend to be pure ground glass opacity
and the T1mi tumors tend to be ground glass with a small solid component
that correlates with invasive adenocarcinoma.
Okay.
So this has been a review of the T category of TNM staging of lung cancer.
Some take home points are that tumors between 1 and 5 cm
are divided into one cm increments,
with each cm getting its own T category.
Remember that if you have a tumor that causes downstream atelectasis
or pneumonitis, or it crosses the minor or major
fissures, then that bumps it up to a T2.
Remember that if you have a separate nodule in the same lobe
or chest wall invasion that bumps it up to a T3.
And then if there's diaphragm, spine or mediastinum invasion, that
brings it to a T4.
All right.
If you have any questions about this topic or any other chest radiology topic,
let me know in the comments below. Thanks.