see also:

• the chest X-ray (CXR)
• acute pulmonary oedema (APO)
• LITFL pleural fluid analysis

• pleural effusion is the collection of fluid other than blood, lymph or pus between the two layers of pleura outside the lung (NB. a collection of blood is a haemothorax, a collection of lymph is a chylothorax while collection of pus is an empyema)
• it may be mobile or loculated
• it may be caused by transudate or an inflammatory exudate (fibrinous, serous or serofibrinous effusion which may become haemorrhagic or purulent)
• if large it may impair respiratory function and require drainage to relieve the pressure upon the lungs

• increased hydrostatic pulmonary capillary pressure
  • acute pulmonary oedema (APO)
• decreased osmotic pressure due to hypoalbuminaemia
  • nephrotic syndrome
  • cirrhosis
• increased intrapleural negative pressure
  • atelectasis
• decreased lymphatic drainage
  • mediastinal tumours

• infection eg. pneumonia, tuberculosis (TB), fungal
• pulmonary infarcts eg. pulmonary embolism (PE)
• inflammatory conditions involving the pleura eg. rheumatoid arthritis, systemic lupus erythematosus (SLE), chronic renal failure, sarcoidosis, etc
• neoplastic conditions
  • mesothelioma, metastases, lung cancer, breast cancer, lymphoma, leukaemia, ovarian tumours, stomach cancer
  • Meig's syndrome - pelvic malignancy, ascites and pleural effusion
• oesophageal perforation
• intra-abdominal conditions
  • pancreatitis
  • intra-abdominal abscess
• trauma
• radiation pleuritis
• ovarian hyperstimulation syndrome
• pericarditis
• post-op eg. CABG
• drug-induced pleural disease
• asbestosis
• yellow nail syndrome - yellow nails, lymphoedema, pleural effusions
• chronic renal failure
• trapped lung
• fistula