Pleural effusion and empyema
Pleural effusion is an excess of fluid in the pleural space. Normally, this space contains a small amount of extracellular fluid that lubricates the pleural surfaces. Increased production or inadequate removal of this fluid results in pleural effusion. Empyema is the accumulation of pus and necrotic tissue in the pleural space. Blood (hemothorax) and lymph or chyle (chylothorax) may also collect in this space.
Causes
The balance of osmotic and hydrostatic pressures in parietal pleural capillaries normally results in fluid movement into the pleural space. Balanced pressures in visceral pleural capillaries promote reabsorption of this fluid.
Transudative pleural effusion
Excessive hydrostatic pressure or decreased osmotic pressure can cause excessive amounts of fluid to pass across intact capillaries. The result is a trans-udative pleural effusion, an ultrafiltrate of plasma containing low concentrations of protein. Such effusions commonly result from heart failure, hepatic disease with ascites, peritoneal dialysis, hypoalbuminemia, and disorders resulting in overexpanded intra-vascular volume.
Exudative pleural effusion
Exudative pleural effusions result when capillaries exhibit increased permeability with or without changes in hydrostatic and colloid osmotic pressures, allowing protein-rich fluid to leak into the pleural space.
Exudative pleural effusions occur with tuberculosis, subphrenic abscess, pancreatitis, bacterial or fungal pneumonitis or empyema, malignancy, pulmonary embolism (with or without infarction), collagen disease (lupus erythematosus and rheumatoid arthritis), myxedema, and chest trauma.
Empyema
Usually associated with infection in the pleural space, empyema may be idiopathic or may be related to pneumonitis, carcinoma, perforation, or esoph-ageal rupture.
