Mediastinum

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This is a quick tutorial on the mediastinum. The mediastinum is the central compartment in the thorax. It contains a lot of important structures. The mediastinum separates the pleural cavities. The pleural cavities are the structures that contain the lungs. The lungs are lined by pleura and the pleural form the pleural cavities. You can see the lungs on either side and the medial wall of these pleural cavities forms the lateral wall of the mediastinum.

The mediastinum is one of these things in anatomy that has different borders – lateral borders, posterior, anterior, superior and inferior borders to define it.   The lateral borders of the mediastinum are made up by the medial aspect of the pleural cavities.

 

Inferiorly, you have the diaphragm, which forms the inferior boundary of the mediastinum. Superiorly, the mediastinum is bounded by the superior thoracic aperture or the thoracic inlet. The thoracic inlet is sort of this bony ring formed by the first rib articulating with the first thoracic vertebra posteriorly.  You can’t quite see it, it’s just the first thoracic vertebra at the back. And so you’ve got the costal cartilage and the manubrium here.   It’s this bony ring here which is referred to as the superior thoracic aperture. This forms the top, superior boundary of the mediastinum.

 

The posterior border of the mediastinum is made up of the bodies of the thoracic vertebra.   You can see the thoracic vertebra.   The bodies of the thoracic vertebra make up the posterior wall of the mediastinum.

 

Anteriorly, you have the manubrium and the sternum.   These makes up the anterior wall.

 

The mediastinum is this central compartment of the thorax. And just to cover the boundaries again, you’ve got the lateral boundaries which are formed by the pleural cavities on either side. You’ve got the superior boundary, which is formed by the superior thoracic aperture or the thoracic inlet. You’ve got the inferior boundary made up by the diaphragm. And you’ve got the posterior and anterior boundaries made up by the bodies of the thoracic vertebra and the manubrium and sternum respectively.

 

The mediastinum can be separated into superior and inferior halves.   You’ve got the superior half with its inferior boundary at the upper level of the pericardium and the inferior half of the mediastinum below.   The inferior half can actually be divided into three compartments. You’ve got the anterior, middle and posterior mediastinum.   You’ve got the superior and inferior division and the inferior division can be subdivided into anterior, middle and posterior.

 

Just to talk a little bit about the contents of the mediastinum. You’ve obviously got a lot of important structures that run through this. You can see you’ve got the trachea here. Posterior to that, you’ve got the esophagus, which run through the mediastinum. You’ve got the great vessels of the heart – the vena cava, the aorta, the pulmonary trunk and the pulmonary veins. You’ve got the phrenic nerve, so the nerve which innervates the diaphragm on either side. And then you’ve got some things which aren’t visible in this model. You’ve got the thymus and you’ve got the thoracic duct. The thoracic duct is the largest structure of the lymphatic system, the largest vessel of the lymphatic system, which drains into the left brachiocephalic vein. You’ve also got lymph nodes of the central chest.

 

Obviously, you’ve got the heart, you’ve got the great vessels of the heart, the esophagus, the trachea, the phrenic nerves, the thoracic duct, the thymus and you’ve got lymph nodes up the central chest.   That’s the mediastinum.