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M01.05.003 Middle Mediastinum
The mediastinum is the central compartment of the thoracic cavity, situated between the pleural sacs of the lungs. It houses most thoracic organs and serves as a passage for structures traveling between the thorax and abdomen.
Divisions of the Mediastinum
The mediastinum is divided into:
- Superior Mediastinum:
- Extends upward to the superior thoracic aperture.
- Inferior Mediastinum:
- Extends downward to the diaphragm.
- Subdivided into:
- Anterior Mediastinum
- Middle Mediastinum
- Posterior Mediastinum
This article focuses on the Middle Mediastinum, covering its borders, contents, and clinical relevance.
Borders of the Middle Mediastinum
| Border | Description |
|---|---|
| Anterior | Anterior margin of the pericardium. |
| Posterior | Posterior border of the pericardium. |
| Lateral | Mediastinal pleura of the lungs. |
| Superior | Imaginary line from the sternal angle to the T4 vertebra. |
| Inferior | Superior surface of the diaphragm. |
Contents of the Middle Mediastinum
Organs
- Heart with its protective sheath, the pericardium.
- Tracheal bifurcation and the left and right main bronchi.
Vessels
| Vessel | Description |
|---|---|
| Ascending Aorta | Arises from the aortic orifice, giving rise to the left and right coronary arteries. |
| Pulmonary Trunk | Gives rise to the left and right pulmonary arteries, facilitating blood flow to the lungs. |
| Superior Vena Cava | Formed by the right and left brachiocephalic veins, it returns deoxygenated blood to the heart. |
Nerves
| Nerve | Description |
|---|---|
| Cardiac Plexus | Located at the base of the heart; contains sympathetic (T1-T4) and parasympathetic (vagus nerve) fibers. |
| Phrenic Nerves | Mixed nerves that provide motor innervation to the diaphragm, descending through the middle mediastinum. |
Lymphatics
- Tracheobronchial Lymph Nodes:
- Located near the trachea and bronchi.
- Often enlarged in lung pathologies.
- Connected by fine lymphatic channels.
Key Points to Remember
- The middle mediastinum is the largest subdivision of the inferior mediastinum.
- Contains vital structures including the heart, great vessels, phrenic nerves, and tracheobronchial lymph nodes.
- The ascending aorta, pulmonary trunk, and superior vena cava originate here but extend into adjacent compartments.
- The phrenic nerves play a crucial role in diaphragmatic movement, essential for respiration.
Clinical Correlation
- Enlargement of tracheobronchial lymph nodes can be indicative of respiratory diseases such as lung cancer or tuberculosis.
- Pathologies affecting the cardiac plexus may present with arrhythmias due to disrupted autonomic innervation.