The pleural cavity is a potential space within the thoracic cavity lined by visceral and parietal pleural membranes
Normally, the pleural apace contains a small physiologic amount of pleural fluid (0.1 mL per kg). An imbalance between normal pleural fluid formation and/or absorption results in accumulation of fluid within the pleural cavity.
The fluid may be either transudative or exudative:
It is thought to be a common condition with an estimated 1-1.5 million new cases in the United States and 200 000-250 000 in the United Kingdom each year (3).
A pleural effusion will only be detected:
Last reviewed 01/2021