The mediastinum is an area found in the midline of the thoracic cavity, that is surrounded by the left and right pleural sacs. It is divided into the superior and inferior mediastinum, of which the latter is larger.
The inferior mediastinum is further divided into the anterior, middle and posterior mediastinum. Every compartment of the mediastinum contains many vital organs, vascular and neural structures that are closely related one to another.
Such a rich content of the mediastinum indicates its significance from the aspect of the anatomy.
Borders: first rib (superior) - T4 (inferior)
Content: thymus, trachea, esophagus, thoracic duct, aortic arch, veins (superior vena cava, brachiocephalic, left superior intercostal), nerves (vagus, phrenic, left recurrent laryngeal), lymphatics, other small arteries and veins
Mnemonic: Try To Eat Toast And Vitamins Now Little Oliver
|Anterior inferior mediastinum||
Borders: T4 (superior) - T9 (inferior); sternum (anterior) - pericardium (posterior)
Content: remnants of the thymus, lymph nodes
|Middle inferior mediastinum||
Borders: T4 (superior) - T9 (inferior); anterior aspect of pericardium (anterior) - posterior aspect of pericardium
Content: phrenic nerve, heart, pericardium, ascending aorta, pulmonary trunk, superior vena cava, pericardiacophrenic artery
|Posterior inferior mediastinum||
Borders: T4 (superior) - T12 (inferior); posterior aspect of pericardium (anterior) - spine (posterior)
Content: descending thoracic aorta, azygos veins, hemiazygos veins, accessory hemiazygos veins, thoracic duct, cisterna chyli, esophagus, esophageal plexus, vagus nerve, greater, lesser and least splanchnic nerves, lymphatics
Mnemonic: on the DATE Vivian Slapped Larry
|Clinical relations||Mediastinitis (inflammation of the structures within the mediastinum)|
- Thoracic cavity
- Lymphatics of the mediastinum
This cylindrical cavity of the chest is enclosed by the thoracic walls and the diaphragm. Superiorly it communicates with the neck, through the superior thoracic aperture.The thoracic cavity houses three compartments: left and right pleural cavities and the mediastinum. The pleural cavities are placed in the lateral parts of the thorax, they contain the lungs and their associated structures. The mediastinum sits centrally, between the pleural cavities.
The mediastinum, or mediastinal cavity, is a visceral compartment of the thoracic cavity. It completely separates the two pleural cavities by being placed longitudinally between them in a median sagittal position. It extends superoinferiorly from the superior thoracic aperture to the diaphragm, anteroposteriorly from the sternum to the bodies of thoracic vertebrae, and laterally from the mediastinal pleura of the adjacent pleural cavities. The main mediastinal contents are the heart, esophagus, trachea, thoracic nerves and systemic blood vessels.
The mediastinum is divided into the superior mediastinum and inferior mediastinum by a transverse plane that extends from the sternal angle (manubriosternal junction), to the intervertebral disc between T4 and T5 vertebrae.
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The superior mediastinum is a space bounded anteriorly by the manubrium of the sternum, and posteriorly by the bodies of T1-T4 vertebrae. Its superior border is an oblique plane extending from the jugular notch of the manubrium to the superior border of T1 vertebra. Whilst the inferior border is a transverse plane extending from the sternal angle to the T4-T5 intervertebral disc.
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The transverse plane separates the superior from the inferior mediastinum. Lastly, the lateral borders are the mediastinal surfaces of parietal pleura on each side.
The contents of the superior mediastinum includes many organs, vessels and nerves;
- Aortic arch
- Brachiocephalic trunk
- Left common carotid artery
- Left subclavian artery
- Internal thoracic arteries
- Superior vena cava
- Left superior intercostal vein
- Brachiocephalic veins
- Phrenic nerves
- Vagus nerves
- Left recurrent laryngeal branch of the left vagus nerve
- Thoracic duct
- Lymph nodes and vessels,
- Other small arteries, veins and nerves
We’ve got you covered with the anatomy of the structures found within the superior mediastinum.
The inferior mediastinum extends from the inferior border of the superior mediastinum to the diaphragm. It is subdivided anterior-to-posterior into three spaces:
- Anterior mediastinum - posterior to the body of the sternum and anterior to the pericardium
- Middle mediastinum - bounded by the pericardium, which encloses the heart and origins of the great vessels
- Posterior mediastinum - posterior to the pericardium and anterior to the vertebrae
Inferior portion of thymus
Mediastinal branches of internal thoracic vessels
Origins of great vessels: pulmonary trunk, ascending aorta, pulmonary veins, superior vena cava, inferior vena cava
Tracheal bifurcation and main bronchi
Descending thoracic aorta and its branches
Azygos and hemiazygos venous systems
Thoracic duct & cisterna chyli
Esophagus and esophageal plexus
Thoracic splanchnic nerves (greater, lesser, least)
on the DATE Vivian Slapped Larry
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New classification of mediastinal compartments
Recently, a group of specialists in thoracic surgery, diagnostic imaging, oncology and pathology developed a new classification for the mediastinal compartments.
This new classification is based on cross sectional images, and divides the mediastinum into three compartments (prevascular, visceral and paravertebral), all of which are bordered superiorly by the thoracic inlet and inferiorly by the diaphragm and limited laterally by the parietal mediastinal pleura.
The prevascular compartment is limited anteriorly and posteriorly by the posterior surface of the sternum and the anterior aspect of the pericardium, respectively. Its name is derived from the fact that this compartment lies anterior to the major vessels of the mediastinum (ascending aorta and its branches, superior vena cava and pulmonary vessels). Its primary contents are the thymus, and the left brachiocephalic vein.
Lying posterior to the prevascular compartment is the visceral compartment which is limited posteriorly by a vertical line that connects a point on each thoracic vertebral body, 1 cm posterior to its anterior border. It contains the trachea, esophagus, heart, the ascending and descending aorta, along with the aortic arch and its branches, the superior vena cava, the pulmonary arteries and the thoracic duct.
The posteriormost division is the paravertebral compartment whose posterolateral borders are formed by a vertical line against the posterior border of the chest wall at the lateral margin of the thoracic spine. Its main contents are the thoracic spine, paravertebral soft tissues, sympathetic trunk and azygos/hemiazygos venous system.
This classification consolidates multiple different classifications used by different medical specialties, facilitating the communication between them.
Lymphatics of the mediastinum
There are several groups of lymph nodes scattered within mediastinum. Most of the mediastinal organs drain into the thoracic duct. The interesting exception is the right side of the heart, which together with the right lung, right sides of head, neck and thorax, drains into the right lymphatic trunk.
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