The mediastinum is an area found in the midline of the thorax 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. In this article, the borders of each section of the mediastinum and their contents will be discussed. Lastly, a pathological condition known as mediastinitis will be mentioned.
The anterior inferior mediastinum starts from the thoracic vertebra T4 and continues to the diaphragm at the level of the thoracic vertebra T9. It extends posteriorly from the body of the sternum and transversus thoracis muscle to the fibrous pericardium.
The middle inferior mediastinum begins in the same area as the anterior inferior mediastinum and finishes also in the same area between the T9 and T10 vertebrae. It extends posteriorly between the width of the fibrous pericardium.
The posterior inferior mediastinum again originates in the same place as the other two subdivisions but extends the deepest, to the vertebra T12. Sagittally, it runs from the posterior aspect of the fibrous pericardium to the vertebral column.
The superior mediastinum contains three visceral organs including the esophagus, the trachea and remnants of the thymus. The nerves that run through this area are three and there are also two different nervous plexuses. The phrenic nerve, the vagus nerve and the left recurrent laryngeal nerve are the singular nerves, while the cardiac plexus branches and the pulmonary plexus branches make up the peripheral neurological plexuses. Arterial and venous constituents are comprised of the superior vena cava, the brachiocephalic veins, the thoracic duct and the aortic arch which includes the brachiocephalic artery, the common carotid artery and the left subclavian artery.
The anterior inferior mediastinum has no major contents save remnants of the thymus and some lymph nodes.
The middle inferior mediastinum contains a single nerve which is the phrenic nerve, the heart and the pericardium. The vessels present include the ascending aorta, the pulmonary trunk, the superior vena cava and the pericardiacoophrenic artery.
The posterior inferior mediastinum has possibly the most anatomical structures. It encompasses the esophagus, the thoracic aorta and its branches which include the posterior intercostal arteries, the bronchial arteries and the esophageal arteries. It also contains the azygos venous system, the hemiazygos and accessory hemiazygos veins, the thoracic duct, the cisterna chyli, the vagus nerve and the esophageal plexus. Lastly, the following branches of the sympathetic trunk are present: the greater splanchnic nerve, the lesser splanchnic nerve and the least splanchnic nerve.
Mediastinitis is a term used to describe the inflammation of the tissue within the chest or the mediastinum. This disorder can be acute or chronic and is quite serious because the infection is in close proximity to so many essential organs and vessels. The most likely cause of this infection today is post surgical complications of cardiovascular or endoscopic surgery. This situation can become chronic, if a patient has an underlying disease such as tuberculosis or they are undergoing radiation therapy. Treatments depend on the patients case and can include therapy or even surgical decompression of the vessels.