• The accumulation of serous fluid within the pleural space is termed pleural effusion. 
• Accumulations of pus, blood, chyle → empyema, haemothorax, chylothorax respectively. 
• In general, pleural fluid accumulates because of either increased hydrostatic pressure or decreased osmotic pressure (‘transudative’ effusion, as seen in cardiac, liver or renal failure), or from increased microvascular pressure due to disease of the pleura or injury in the adjacent lung (‘exudative’ effusion). 

Clinical assessment

• Symptoms (pain on inspiration and coughing) and signs of pleurisy (a pleural rub) often precede the development of an effusion →pneumonia, pulmonary infarction, CTD. 

Investigations

Management

• Therapeutic aspiration: to palliate breathlessness 
  • removing more than 1.5 L at a time →risk of reexpansion pulmonary oedema. 
  • An effusion should never be drained to dryness before establishing a diagnosis, as biopsy may be precluded until further fluid accumulates. 
• Treatment of an underlying cause such as heart failure, pneumonia, pulmonary embolism or subphrenic abscess will often be followed by resolution of the effusion.