Although it is relatively easy to spot the difference between pericardial and pleural effusions on a chest x-ray, in medical training we have less exposure to ultrasound and it takes much more time to get comfortable looking at ultrasounds and knowing what you are looking at.
The first thing to remember with ultrasound and echocardiography is to get multiple windows! Just like any imaging study, ultrasound has its limitations. That’s why we try to squeeze our probe between or under the ribs in various areas of the chest to try and see the heart in different angles. An effusion can be obvious in one angle but be hiding in a different perspective.
This image below shows both a pericardial and pleural effusion. It’s one of my favorite images in the parasternal long (PSL) axis view via echocardiography. The quick and dirty way to tell if this fluid is a pericardial or pleural effusion is to find the descending aorta. The descending aorta is outside of the pericardium. It travels posterior to the heart down the chest. So when we see the heart in this PSL axis view we are cutting the aorta cross-sectionally. This should help bring you to identify the second important structure- the pericardium, or the connective tissue sac that the heart sits in. Knowing where these two structures are will allow you to more easily identify this fluid accurately as either a pericardial or pleural effusion.
The second tip to correctly identify pericardial versus pleural effusions on ultrasound or echocardiography is to practice and get multiple windows! Getting multiple windows, or ultrasound view points of the heart, has the same importance in getting a 2-view chest x-ray. Multiple vantage points lets you better see the same structure from different angles and can help you clarify what you are looking at when it is not so obvious.
For further resources check out the following links I found helpful. A lot of these blogs are fantastic ultrasound information for individuals who want to dive deeper into echocardiography as well as ultrasound.
- SonoSpot: differentiate between pericardial and pleural effusion
- Great videos of both pericardial and pleural effusions from different angles
- Quick read
- Critical Care Sonography
- Less detailed than above but good videos
- Quick read
- Temple Emergency Ultrasound
- Less detailed, single image.
- Quick read
- emDOCS: When Does an Effusion Become Pericardial Tamponade?
- Higher level for residents and fellows with higher level understanding of echocardiography
- Longer read
- Tamponade by Non-Invasive Assessment by Echo
- Greater detail on tamponade from cardiology perspective
- Longer read