So how can you assess for an enlarged cardiac silhouette
or an enlarged heart on a chest x-ray?
This is a very common finding that can have clinical implications.
So let?s take a look at how we can determine this.
On a PA radiograph, you wanna measure the widest diameter of the heart
and the widest diameter of the chest measured from the inside of the right ribs
to the inside of the left ribs to the inside of the thoracic diameter.
The cardiothoracic ratio should be less than 50%.
So let?s take a look at this measurement.
On the left, you see a normal chest x-ray with a normal-sized heart.
You can see how we measure the inside with the thoracic diameter
and the widest portion of the heart.
On the right side, you have a chest x-ray with a cardiac enlargement.
Again, you can see the measurement and you can see that the cardiothoracic ratio
is greater than 50%. So that?s how we know that this patient has cardiac enlargement.
This is performed on a PA chest x-ray.
If we take a look at AP films, which we will in a minute, it?s not as accurate.
On a lateral radiograph, you really can?t assess heart size as well either.
In general, the heart really shouldn?t touch the spine posteriorly on a lateral radiograph
but that?s really the only way we have of determining heart size on a lateral chest x-ray.
Let?s take a look. On the left, we have a normal.
You can see that the heart, the posterior margin of the heart ends before the spine begins.
Here we have the anterior aspect of the thoracic spine
so we have some space in between indicating that this is a normal-sized heart.
On the right, we have cardiac enlargement.
So you can see that the heart comes all the way back to here
and that touches the anterior margin of the thoracic spine.
So this is an indication that there?s cardiac enlargement.
However, as you know, we normally wouldn?t do just a lateral chest x-ray on its own.
It would really always be done with a PA.
So the best way of assessing heart size is to use the PA film.
What are some artifactual causes of cardiac enlargement?
So rotation can actually distort the appearance of the heart
and make it look large when it really isn?t.
suboptimal inspiration makes the diaphragm move upward
and it compresses the heart so the heart again appears large
when there really isn?t any cardiomegaly.
So let?s take a look at this.
We have on the left a film that has suboptimal inspiration.
On the right, we have a patient that has a normal inspiration
and you can see that both on the left the suboptimal inspiration shows that the heart is enlarged.
On the right, the heart looks normal in size.
However, both of these patients actually have a normal-sized heart.
So you really have to make sure that the patient has a good inspiration before you determine heart size.
A portable supine film can actually magnify the appearance of the heart
because it?s in the AP projection.
So let?s take a look at this. This is the portable supine film.
So do you think this heart is enlarged?
It looks like it is.
If you determine the cardiothoracic ratio it actually looks like the heart
is greater than 50% of the thoracic diameter.
However, even though it appears enlarged, because this is performed in the supine position,
and the portable AP technique, this heart is actually normal in size.
So the cardiothoracic ratio measured on a portable film or any AP film is actually not very accurate.
Again, let?s take a look at this.
On the left, we have a normal-sized heart and on the right,
we have true cardiac enlargement as seen on AP portable film.
It?s a little bit hard to determine; the right film actually looks just like the one that we saw
a little while ago where the heart looked enlarged but it really wasn?t.
So again, the AP portable film is really not the best way to assess heart size.
So pectus excavatum can also cause a heart that appears artificially enlarged.
It?s compressed between the sternum and the spine
and that can cause artifactual cardiac enlargement.
So something to keep in mind again as you take a look at heart size.
The two major causes of an enlarged cardiac silhouette are cardiomegaly
which is the most common cause of the enlarged cardiac silhouette.
However, pericardial effusion can also cause the appearance of an enlarged cardiac silhouette
on a chest x-ray.
So pericardial effusion is fluid between the visceral and the parietal pericardium.
It results in the appearance of an enlarged cardiac silhouette
and you can see here on the CT film, that there?s fluid, low-density fluid right here
surrounding the heart. So this is a CT image of a pericardial effusion.
On a radiograph however, the heart has, what's called the ?water bottle? appearance
and we?ll take a look at that in a little bit.
So let?s take a look at some signs of chamber enlargement.
Again, radiology is all about pattern recognition.
So let?s keep these films in mind so you can recognize the pattern of these enlarged chambers.
So what do you think is enlarged here?
This patient does have an enlarged heart.
The cardiothoracic ratio is likely greater than 50%.
So which portion of the heart is enlarged?
Here we have a PA and a lateral, and you can see that it?s the left heart margin that looks enlarged.
On the lateral, this is seen posteriorly.
So this is an example of left ventricular enlargement.
If you remember the anatomy of the heart, the left side of the heart is the left ventricle
and so that?s how you know that this is left ventricular enlargement.
The right heart margin actually looks pretty normal on this film.
How about this one?
So let?s take a good look here.
So on the left we have the abnormal film and on the right,
we have a comparison of a normal film so you can see what the difference is between the two.
So it?s the superior left margin of the heart that looks enlarged.
If you remember, this actually represents the left atrium.
So this is an example of left atrial enlargement.
How about this one?
So again, we have the abnormal film on the left and then we have a normal on the right.
So now, it?s the right heart margin that looks bulky.
The left actually looks pretty normal.
So this is an example of right atrial enlargement
because again, the right atrium forms the right heart border.
This is an example of a CT image from the same patient.
So again, you can see here that the right atrium forms the right heart border
and the left ventricle forms the majority of the left heart border.
So what about this heart?
This heart has a slightly unusual appearance.
What do you think is causing this enlarged cardiac silhouette?
So this is an example of a pericardial effusion.
This is the appearance of the ?water bottle? heart that we mentioned earlier.
So this is another example of why the cardiac silhouette can appear enlarged on a chest x-ray.
So again, the two major causes of cardiac enlargement are cardiomegaly and pericardial effusion.
You can have the entire cardiac silhouette being enlarged
which means the entire heart is enlarged or we have a large pericardial effusion
or you can have specific chamber enlargement which we reviewed as well.