Pleural effusion is excess fluid that accumulates in the
pleural cavity, the fluid-filled space that surrounds the
lungs. This excess can impair
breathing by limiting the expansion of the lungs. Various kinds of pleural effusion, depending on the nature of the fluid and what caused its entry into the pleural space, are
hydrothorax (serous fluid),
hemothorax (blood),
urinothorax (urine),
chylothorax (chyle), or
pyothorax (pus).
Pneumothorax is the accumulation of
air in the pleural space.