Anatomical Definition of the Chest Cavity
The chest cavity (thoracic cavity) is the space enclosed by the thoracic cage that extends from the thoracic inlet superiorly to the diaphragm inferiorly, and from the sternum anteriorly to the vertebral column posteriorly, containing the lungs, heart, great vessels, esophagus, trachea, and lymphatic structures. 1, 2
Anatomical Boundaries
The thoracic cavity has clearly defined borders that establish its three-dimensional space:
- Superior boundary: The thoracic inlet at the top of the first rib 1
- Inferior boundary: The diaphragm, typically extending down to the twelfth floating rib or approximately the L2 vertebral body level 1
- Anterior boundary: The sternum and anterior chest wall 1
- Posterior boundary: The vertebral column and paravertebral spaces 1
- Lateral boundaries: The ribs, intercostal muscles, and chest wall extending to the costovertebral joints 1
Internal Compartmentalization
The chest cavity is subdivided into distinct anatomical compartments that organize its contents:
Mediastinum
The central compartment lying between the lungs, which can be divided into four traditional compartments (superior, anterior, middle, and posterior) or three modern compartments (anterior/prevascular, middle/visceral, and posterior/paravertebral). 2 This region contains vital structures including the heart, great vessels, esophagus, trachea, and lymphatics. 2
Pleural Cavities
The potential spaces on each side of the mediastinum, bounded by two serous membrane layers:
- Parietal pleura: The outer layer attached to the chest wall, diaphragm, and mediastinum 3, 4
- Visceral pleura: The inner layer covering the lung surfaces and adjoining structures 3, 4
- Pleural space: The thin potential space between these layers containing 5-10 mL of pleural fluid, maintaining a pressure of approximately -4 mmHg at rest 1, 4
The pleural cavity extends into specific recesses including the costodiaphragmatic and costomediastinal recesses. 1
Functional Considerations
The chest cavity functions as a protective bellows-like structure with the diaphragm as the primary moving component. 3 The elastic, serous, and lubricating properties of the pleural membranes reduce friction during respiratory movements, with mesothelial cells containing surface microvilli that enmesh hyaluronic acid-rich glycoproteins for lubrication. 3
The confined nature of the thoracic cavity creates important cardiopulmonary interactions, as changes in intrathoracic pressure directly affect cardiac filling, venous return, and ventricular function. 5
Clinical Relevance for Interventions
For needle decompression procedures, the chest cavity is accessed at specific intercostal spaces, with the pleural cavity typically located beneath the chest wall at depths varying by location (2nd midclavicular line versus 5th midaxillary line). 1
For radiation therapy planning, the thoracic cavity is defined to include the lung-chest wall interface laterally, the mediastinal pleura (including retrosternal fat) medially, the ipsilateral pericardium above the diaphragm, and extending to the diaphragmatic crura and anterior preaortic space below the diaphragm. 1