- pleural space
- Also called pleural cavity.
The cavity that exists between the lungs and underneath the chest wall. It is normally empty, with the lung immediately against the inside of the chest wall. In some diseases, fluid can build up in this space (a pleural effusion). In trauma, air can enter this space (a pneumothorax). Under either condition, excessive fluid or air in the pleural space can cause difficulty breathing since the lung is prevented from inflating fully.