When fluid collects between the parietal and visceral layers of the pleura
Causes
Can be classified as transudate or exudate according to their protein concentration
Transudate (< 30g/L protein):
- heart failure (most common transudate cause)
- hypoalbuminaemia (liver disease, nephrotic syndrome, malabsorption)
- hypothyroidism
- Meigs' syndrome - triad of benign ovarian tumour, ascites, pleural effusion
Exudate (> 30g/L protein):
- infection: pneumonia (most common exudate cause), TB, subphrenic abscess
- connective tissue disease: RA, SLE
- neoplasia: lung cancer, mesothelioma, metastases
- pancreatitis
- pulmonary embolism
- Dressler's syndrome
- yellow nail syndrome
PC