So what are some imaging findings of free flowing effusions on an upright film?
The most common findings are blunting of the costophrenic angles and the meniscus sign.
So what does blunting of the costophrenic angle mean?
The posterior costophrenic angle is blunted with only about 75 mL of fluid.
Normally, if you remember, the costophrenic angles have very sharp margins.
When they have blunting with fluid the margin actually becomes less sharp
and we'll take a look at an example.
The lateral costophrenic angle is blunted with about 250 mL of fluid,
so it's a much more sensitive evaluation for you to evaluate
the posterior costophrenic angle which is blunted with only a small amount of fluid.
Let's take a look, this is a lateral radiograph coned down to the inferior part of the lung
and this right here is the posterior costophrenic angle.
When you compare it with the one on the other side
you can tell that this one remains sharp while this one is blunted
so it's no longer sharp. This is a result of a pleural effusion.
On the frontal view here which is coned down to the right lower lung,
you can again see blunting of this lateral costophrenic angle here.
Again, this is because of a small pleural effusion.
The other sign that we look for is called the meniscus sign.
This is the formation of a U-shape as the fluid rises along the sides of the pleura
and you can see that outlined here in green.
The patient has a left pleural effusion which forms a U which is called the meniscus.
If a patient is unable to stand upright,
another way to evaluate a pleural effusion
and to tell whether it's free falling is to perform a decubitus film.
Again, because of the gravity dependence you have layering of a free-flowing effusion.
This can actually detect the smallest 15 mL of fluid
so it's a very sensitive way to evaluate a free-flowing effusion
and you can see that this patient is lying on the right side and you have a meniscus,
a very large U-shape that forms in the dependent portion of that lung
indicating that there's a pleural effusion on that side that's free-flowing.
Let's take a look at this.
You have an axial CT image on the left and then you have a radiograph on the right.
Can you see the findings here' This is actually a CT detected pleural effusion.
CT is very sensitive for the detection of a pleural effusion
and you can see here bilateral, small pleural effusions.
The radiograph is actually normal so the one thing that you wanna look for
on a frontal radiograph is blunting of the costophrenic angles.
So we have both costophrenic angles here which remain sharp.
Looking at the radiograph, we really would not have identified the pleural effusion
because it's very small.
The CT however was able to detect it.
This is an example of what we call pseudotumor,
so this is accumulation of fluid within an interlobular fissure.
It's lenticular shape or lens shape and is most often associated with CHF
so you have to be aware that even though it's called pseudotumor
it has no association with a malignancy.
It's called that only because of its shape because it looks mass like on a radiograph.
Let's take a look at this case.
This is an example of a hemithorax opacification.
This has multiple differentials and one of them includes massive pleural effusion.
We have shift of the mediastinum away from the side of effusion
because the effusion causes mass effect on the side that it presents.
So we've gone over a multiple different findings of pleural effusion.
Hopefully, you can keep these in mind
because you will likely see many causes of pleural effusion in the future.