Pleural effusion is bilateral in 70% of cases of CHF.
When unilateral, it is slightly more often on the right side than on the left side. 
There has to be at least 175 ml of pleural fluid, before it will be visible on a PA image as a meniscus in the costophrenic angle.
On a lateral image effusion of > 75 ml can be visible. 
If pleural effusion is seen on a supine chest film, it means that there is at least 500 ml present.
On the left images of a patient who has bilateral pleural effusions. 
Notice that it is more evident on the lateral view. #Clinical #Radiology #CXR #CHF #Pleural #Effusion #PleuralEffusion #RadiologyAssistant