- Characteristics of the fluid depend on the underlying pathophysiologic mechanism.
- Fluid can be transudate, nonpurulent exudate, pus, blood, or chyle.
- A small amount of fluid is normally present in the pleural space.
- The parietal pleura continuously produce the fluid, which is absorbed by the visceral pleura and by the lymphatics of the parietal pleura.
- The hydrostatic, colloid osmotic, and tissue pressures affect circulation of the fluid. Alteration of 1 or more of these factors causes abnormal accumulation of fluid in the pleural space and is the primary mechanism of transudative effusions.
- Injury to the pleura or subpleural lung parenchyma can cause increased vascular permeability and a shift of fluid from the pulmonary interstitium. This mechanism is primarily seen in exudative effusions, such as effusion associated with pneumonia and infarction.
- Most pleural effusions are secondary to CHF, malignancy, pneumonia, or pulmonary emboli.
- Dyspnea is the main clinical symptom directly related to pleural effusion. The degree of respiratory function compromise is a function of the size of the effusion and the presence of associated lung parenchymal abnormalities.
- The pleuritic chest pain associated with pleural irritation is localized, sharp, and severe. It is exacerbated by deep inspiration or coughing. The development of effusion may relieve the pleuritic pain. The mass effect associated with large pleural effusions can cause dyspnea.
 Imaging Findings
Patient #2: Small bilateral pleural effusions that layer with decubitus views
 See Also
 External Links
- Lababede, Omar. E-medicine radiology article.