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Date of last update: 10/19/2017.

Forum Name: Chest symptoms

Question: Pleural Effusion: Why's it usually on the right side?

 atomajames - Mon Mar 23, 2009 10:51 am

Hi there,
I'm a medical student, and currently confused on one of my companion's question: why pleural effusion usually occurs on the right side of the lung? In bilateral pleural effusion, it's mostly the right side that has a larger amount of fluid.

Well, I then tried to google some answers, but found a bit, to nothing, of information. In one site, it says that in CHF patients, pleural effusion tends to occur on the right side because of patient's habit to lie down on his/her right side to find some comfort. Well, that makes sense. But..... why in most cases of pleural effusion, it always occur first in the right side? For example, in Dengue Haemorrhagic Fever, the pleural effusion occurs around 85% in the right side (according to one site I found). If it occurs bilaterally, the amount of fluid is usually greater than the left side.

What's the possible cause of this phenomenon? Is it the anatomy? Vascular aspect? I hope I can find some answers here. Thank you.
 John Kenyon, CNA - Tue Mar 24, 2009 10:38 pm

User avatar Hello --

Excellent question! In my experience this has been answered most often (and I've asked it more than a few times) that it's largely an anatomical phenomenon. Look at the way the right pleural cavity is occupied vs. the left and you can see it's a natural reservoir of first choice based on gravity and resistance. That's my best answer and I feel it is at least a valid one, if perhaps not the only explanation. I think it's the most logical one, and the majority of doctors (including some thoracic surgeons) have answered this way -- or simply denied the phenomenon even exists. I've seen it enough times to believe it's not only true but that the vast majority who blame this on anatomy are correct.

I hope this is helpful. Best of luck to you.
 atomajames - Mon Mar 30, 2009 3:03 am

Thank you so much for answering,
I've thought that it might be caused by anatomical structure, but couldn't explain it. Your answer seems so logical by now.
Aside from posting in this forum, I've come across to some answer from other doctors that I asked from. The most interesting one is: because left lung consists of 2 lobes, and the right one is 3, then it's most likely that pleural effusion will have a tendency to occur on the right side. Why? At least, in Dengue Hemorrhagic Fever, one of the systemic failure is plasma leakage. The right lobe of the lung provides more mass of organ than the left side, thus the amount of blood vessels are greater on the right side than the left side. So, pleural effusion tend to occur first, or more, on the right side.
But still, that answer is quite similar to the one you posted, and valid. Thank you so much.

PS: any other opinions?

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