Borders, divisions and contents of the mediastinum
Upon completing this study unit you will be able to:
- Understand the boundaries of the mediastinum and list the anatomically related structures.
- Describe the divisions of the mediastinum.
- List the mediastinal contents and place them correctly into each division.
The mediastinum is a compartment of the thorax located in the midline of the body, that contains most of the thoracic viscera, apart from the lungs. It extends vertically from the superior thoracic aperture to the diaphragm and is bounded laterally by the medial surfaces of the pleura.
The thoracic plane (of Ludwig), is an imaginary line extending from the sternal angle, anteriorly, to the T4-T5 intervertebral space, posteriorly. This plane divides the mediastinum into superior (above the thoracic plane) and inferior (below the thoracic plane) mediastinal divisions.
The inferior division is further subdivided into anterior, middle and posterior compartments by the pericardial sac. Structures located anterior to the pericardial sac belong to the anterior mediastinum, whereas those located posterior to pericardial sac are said to be structures of the posterior mediastinum. Those located in and around the pericardial sac belong to the middle mediastinum.
Some structures course longitudinally both through the superior and inferior mediastinum: esophagus, azygos veins and vagus and phrenic nerves.
The video below will give you a better understanding of the boundaries, divisions and contents of the mediastinum.
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Take a closer look at the borders, divisions and contents of the mediastinum from a lateral perspective.
Now explore the associated structures of the mediastinum from an anterior view.
Superior: Superior thoracic aperture (delineated by the manubrium of the sternum, superior border of the first rib and body of vertebra T1)
Anterior: Sternum and costal cartilages of 1st-5th ribs
Posterior: Vertebral bodies of superior thoracic vertebrae
Lateral: Parietal pleura of each lung
Thoracic plane: Extends from sternal angle to vertebrae T4/5 intervertebral space
Superior mediastinum: Above thoracic plane
Inferior mediastinum: Below thoracic plane, further subdivided into anterior, middle and posterior compartments, according to relations with pericardial sac
Superior mediastinum: Thymus, trachea, superior part of superior vena cava, aortic arch and its branches (brachiocephalic trunk, left common carotid artery and left subclavian artery, esophagus
Anterior mediastinum: Some remnants of the thymus
Middle mediastinum: Pericardial sac and heart; roots of superior and inferior vena cava; pulmonary trunk, arteries and veins; root of aorta; main bronchi; pericardiacophrenic arteries and veins
Posterior mediastinum: Descending thoracic aorta and its branches; azygos veins, esophagus
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