Often, you cannot. Occasionally, the lateral view will show the outline of the effusion anterior to the heart shadow. There will be a thin lucent (relatively black) line adjacent to the heart representing epicardial fat‚ (actually associated with the visceral pericardium), then a fatter soft-tissue stripe representing the effusion, and then most anteriorly, a thin lucent fat stripe representing the pericardial fat‚ (mediastinal fat).
Is the chest x-ray sensitive for diagnosing a pericardial effusion?
The chest radiograph is not at all sensitive to even moderate amounts of pericardial fluid. Echocardiography is the most sensitive method for distinguishing pericardial fluid from myocardial dilatation.
What is the sine qua non of significant pulmonary arterial hypertension on the chest x-ray?
Calcification in the pulmonary arteries (a very rare finding).
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A more common sign is big distorted globs where the pulmonary arteries should be, although this appearance is sometimes difficult to differentiate from hilar adenopathy. On the frontal view, the left pulmonary artery always looks bigger because its profile in the left mediastinum and hilum is closer to its origin. The lateral view is quite helpful in distinguishing pulmonary hypertension from adenopathy. An enlarged left pulmonary artery looks like an aorta curving over the left upper lobe bronchus, and an enlarged right pulmonary artery makes a large circle anteroinferior to the carina. If these shadows are distinguishable, pulmonary hypertension can be differentiated from adenopathy.
What are the causes of pulmonary arterial hypertension?
The most common cause is lung disease‚ chronic obstructive pulmonary disease‚ or hypoxia of multiple causes. Lung disease usually causes enlarged pulmonary arteries that seem to taper quickly but do not appear anatomically distorted centrally. Three diseases cause marked pulmonary hypertension with distorted-looking arteries and normal-looking lungs: idiopathic pulmonary hypertension (in young females), chronic pulmonary emboli, and Eisenmenger reaction (from chronic shunt).