So now let's talk a little bit about pleural effusion,
a very common abnormality that's found within the chest.
Pleural effusion is accumulation of fluid within the pleural space.
Pleural fluid is physiologically produced at the capillary bed
of the parietal pleura but it's usually absorbed by the parietal pleural,
lymphatics and the visceral pleura.
There are different causes of pleural effusion
including increased rate of formation, decreased rate of absorption
and direct extension from the peritoneum through the diaphragm.
So let's just take a look at the anatomy one more time,
so we have here the lung which is surrounded by the visceral pleura
which is right here, the inside layer.
The outside layer is called the parietal pleura
and in between the two is the pleural space where the fluid accumulates.
So pleural effusions are characterized by their protein content,
they can be transudative in which they have a very low protein content
and this is usually the result of an increase in hydrostatic pressure
or decrease an osmotic pressure and causes include congestive heart failure,
cirrhosis, nephrotic syndrome or any cause of hypoalbuminemia.
They can also be exudative or have a high protein content
and these are usually the result of an inflammatory or an infectious process
like pneumonia. They could be cause by any kind of cancer within the lung.
Hemothorax is considered as high protein content diffusion.
Empyema which is the collection of infected fluid
or possibly a pulmonary embolism that results in infraction.
So the infracted tissue can result in a pleural effusion
that has a high protein content.
Pleural effusion are also characterized by whether they're bilateral or unilateral.
The most common bilateral effusions are caused by CHF
and a little bit less commonly lupus.
Unilateral pleural effusion are often caused by malignancy,
infection, trauma, pulmonary embolism or cirrhosis.
And again these are somewhat general categorizations
so each of these can also cause the opposite type of effusion.
So what is a subpulmonic pleural effusion?
Within the pleural space, that's just above the diaphragm,
there could be an accumulation of fluid which is really best seen on an upright film.
So you can see here that there's elevation of the right hemidiaphragm
much significantly higher than the left hemidiaphragm
and this is really the only finding of a subpulmonic effusion.
So if you see a symmetric elevation of the hemidiaphragm
one of the things to consider is a subpulmonic pleural effusion.
Often pleural effusion start in the subpulmonic location
because of gravity and then they arise and move up to the sides.
So there are two different categories of pleural effusion in terms of location.
One is a free-flowing effusion and this is a normal gravity dependent flow
within the pleural space. These are usually the most common
and the fluid redistributes based on patient's positioning.
So on the left, we see an image of a patient that supine
and you can see that the fluid layers throughout the right lung.
The entire right lung appear somewhat hazy
with the apex being a little bit less hazy
because more of the fluid is located inferiorly.
On the right, you have a semi-upright film
which is obtained a few minutes later in the same patient.
And you can see that the fluid has now dropped down inferiorly
because the patient has gone into a semi upright position.
And so now the fluid because of gravity is a little bit more inferiorly located.
Pleural effusion can also be loculated or walled off
and this is usually a cause of adhesions
in which you have no change in shape or location
with changes in patient position.
So it's a small collection of fluid that really can't move around at all
and you can see an example of it here.
The patient has bilateral loculated pleural effusions
with even though the patient is upright in this position
you can see that the fluid remains in the upper part of the lung on both sides.
So these cannot be drained as well as the free-flowing effusion.
So it's important to recognize these for therapeutic reasons
because they're walled-off and they often contain multiple septations
eventhough you try to drain it not all of the fluid will come out.