Definition of the Pleural Space
The pleural space is a potential anatomical space between the visceral pleura (covering the lungs) and the parietal pleura (lining the chest wall), normally containing only 5-10 mL of fluid and maintaining a negative pressure of approximately -4 mmHg at rest. 1, 2
Anatomical Structure
The pleural space is formed by two serous membrane layers that fold back onto themselves: the visceral pleura adheres to the lung surface and adjacent structures (blood vessels, bronchi, nerves), while the parietal pleura attaches to the chest wall, diaphragm, and mediastinum 3
This thin space between the two pleural layers is termed a "potential space" because under normal physiological conditions, the layers are closely apposed with minimal separation 2, 3
The pleural cavity normally contains approximately 10 mL of fluid in each hemithorax, which serves as a lubricant allowing smooth lung movement during respiration 2, 3
Physiological Function
The negative intrapleural pressure (approximately -4 mmHg at rest) is essential for maintaining lung expansion and creating tight mechanical coupling between the lung and chest wall 1, 4
Pleural fluid is filtered from systemic capillaries in the parietal pleura down a small pressure gradient into the pleural space, with secretion greatest at the apex 1
Under normal conditions, the visceral pleura plays an insignificant role in pleural fluid turnover 1
Drainage occurs predominantly through stomata (openings) in the parietal lymphatics located between parietal mesothelial cells, with the highest concentration at the diaphragm and mediastinum 1, 4
Clinical Significance
The parietal pleura is highly sensitive to pain due to rich sensory innervation, while the visceral pleura lacks sensory innervation and is insensitive to pain 3
Diseases of the pleura manifest as thickening of pleural membranes or abnormal accumulation of air (pneumothorax) or liquid (pleural effusion) 2
The pleural space extends posteriorly to approximately the L1 level in most individuals, with the posterior costophrenic sulci extending on average at least 3 cm below the lateral costophrenic sulci 1