Pleural effusion is the presence of excess fluid in the pleural space.
This fluid can be serous,exudative,blood or chyle.
The most common causes of transudaitve effusions is CHF.Nephrotic syndrome is another cause.
The four principal causes of exudative effusions are,
1)Microbial invasion through direct extension of a pulmonary infection or blood borne seeding
2)Cancers of lung,breast or lymphoma
3)Pulmonary infarction
4)Viral pleuritis
Other causes include tuberculosis, SLE,rheumatoid arthritis,uremia,previous thoracic surgery,esophageal rupture or pancreatic disease, intra-abdominal abscess and any trauma.