Pleural effusion (aka water on the lung) is excess fluid accumulating between the 2 pleural layers that surround the lungs.

• Although normally containing fluid, excessive amounts can impair breathing by limiting the expansion of the lungs during inspiration

• 5 types of fluid can accumulate in the pleural space, including:
  • Hydrothorax (serous fluid)
  • Hemothorax (blood)
  • Urinothorax (urine)
  • Chylothorax (chyle)
  • Pyrothorax (pus)

• Transudative pleural effusion, involving increased permeability of the capillaries in the lung, due to release of cytokines or inflammatory mediators (e.g. vascular endothelial growth factor) from the platelet-rich blood clots. It is caused by:
  • Congestive heart failure
  • Liver cirrhosis
  • Hypoproteinemia
  • Nephrotic syndrome
  • Acute atelectasis
  • Myxedema
  • Peritoneal dialysis
  • Meigs syndrome
  • Obstructive uropathy
  • ESRD (end stage kidney disease)
• Exudative pleural effusion, caused by:
  • Bacterial pneumonia
  • Cancer, including lung cancer, breast cancer, and lymphoma
  • Viral infection
  • Pulmonary embolism

• CXR, showing as an area of whiteness, as there is abnormal fluid collection

Source: Wikimedia

• Pulmonary edema (water IN the lung)
• Pneumothorax (accumulation of AIR in the pleural space)