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StatPearls . Endowment Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

The thoracic mediastinum is the compartment the runs the size of the thoracic cavity between the pleural bag of the lungs. This compartment extend longitudinally indigenous the thoracic inlet to the superior surface of the diaphragm. Back there room no physical barriers between compartments other than the pericardium, the mediastinum is frequently discussed based upon subdivisions. The four-compartment model divides the mediastinum into the superior, anterior, middle, and also posterior portions. The mediastinum residences many crucial structures consisting of the heart, great vessels, trachea, and also essential nerves. It additionally functions together a protected pathway for structures traversing native the neck, superiorly, and also into the abdomen, inferiorly. The mediastinum is also clinically significant due come the range of physical anomalies and also pathologies the can occur in this region.


Structure and also Function

The mediastinum is split compartmentally and consists the subdivisions the house and support an essential structures within the thorax. Listed below are the boundaries of each an ar of the mediastinum.

Each region of the thoracic mediastinum contains unique structures. Noted below room the various regions of the thoracic mediastinum and also a high-level rundown of their components.


Superior Mediastinum:
Organs: thymus, trachea, esophagus
Arteries: aortic arch, brachiocephalic trunk, left usual carotid artery, left subclavian artery
Veins and also lymphatics: remarkable vena cava, brachiocephalic veins, the arch that the azygos, thoracic duct
Anterior Mediastinum:
Organs: thymus
Arteries: internal thoracic branches
Veins and also lymphatics: internal thoracic branches, parasternal lymph nodes
Middle Mediastinum:
Organs: the heart and also its great vessel roots, trachea and main bronchi
Arteries: ascending aorta, pulmonary trunk, pericardiacophrenic arteries
Veins and also lymphatics: remarkable vena cava, pulmonary veins, pericardiacophrenic veins
Posterior Mediastinum:
Organs: esophagus
Arteries: diminish thoracic aorta
Veins and lymphatics: azygos hemiazygos veins, thoracic duct

Each region of the mediastinum deserve to be thought about to serve a major function.

The remarkable mediastinum is essentially a conduit room allowing structures to pass in between the head, neck, and thorax.<1><2><3> The anterior mediastinum is protective in nature and filled v connective and also fatty tissue that cushions and supports the thymus and also the crucial cardiac structures simply posterior to it.<2><5> The middle mediastinum residences the heart and the root of the an excellent vessels.<2><5><6><7> The posterior mediastinum, which have the right to be thought of together a extension of the remarkable mediastinum, additionally serves together a conduit. That provides an are for the i of structures between the thoracic and abdominal muscle cavities.<2><5>


Blood Supply and also Lymphatics

The thoracic mediastinum residences the heart and also the good vessels. Due to this anatomical configuration, the thoracic mediastinum has numerous blood ship traveling through it.<1><2><5><6><7> Since the lymphatic system carefully integrates into the cardiovascular system, there is also a far-ranging presence of lymphatics in this area.<1><2><5><10>

The remarkable mediastinum has the arch of the aorta and also its three associated significant branches: the brachiocephalic trunk, the left common carotid, and the left subclavian arteries.<1><2><5> In enhancement to these huge arteries, some smaller sized branches of the aorta are existing within the remarkable mediastinum including the thymic branches the the internal thoracic arteries, the proximal portions of the pericardiophrenic arteries, and also the third and 4th posterior intercostal arteries.<11><9><3> The majority of lymphatic drainage in this an ar coalesces at the thoracic duct, i m sorry empties right into the bloodstream at the left subclavian vein.<1><4><5><10>

The interior thoracic arteries descend inferiorly and deep come the lateral borders of the sternum. These arteries exit the anterior thoracic mediastinum inferiorly and branch into the musculophrenic arteries and also superior epigastric arteries.<11> Lymphatics in this region include the parasternal, pericardial and superior diaphragmatic lymph nodes.<12><5><6><10>

The middle thoracic mediastinum, bounded through the pericardium, consists of the coronary arteries and also its connected branches. The lymphatics within the pericardium are a facility network of ship that permeate all great of the cardiac tissue. This vessels ultimately drainpipe posteriorly towards the pre-tracheal lymph nodes that lie between the aorta and the trachea.<12><6><10>

The posterior thoracic mediastinum has the diminish aorta together it process slightly left the midline down in the direction of the diaphragm. The most notable arterial branches in this region are the proximal sections of the intercostal arteries. The lymphatics the this an ar include the thoracic duct, retrocardiac lymph nodes, diaphragmatic lymph nodes, posterior mediastinal lymph nodes, and also prevertebral lymph nodes.<1><2><5><10>


Nerves

In the premium mediastinum, there room two broad categories that nerves passing in ~ the region, nerves that originate superior to the thorax and nerves the originate in ~ the thorax.

The premium thoracic mediastinum includes the left and right phrenic nerves (C3 - C5), the left and also right vagus nerves, and other associated vagal branches including the esophageal plexus, the worse cervical cardiac branches, the thoracic cardiac branches, and the recurrent laryngeal nerves. Together for the nerves originating from within the thorax, there is the superior section of the sympathetic trunk (T1 v T4) and its linked sympathetic branches such as the thoracic cardiac and pulmonary branches.<8><13>

The anterior mediastinum does not contain any major named nerves.<2><8><5><8>

The center mediastinum is densely innervated by the autonomic nervous system and also somatically innervated by the phrenic nerves. The sorry innervation arises from branches that the forgiveness trunk approximately the T2 with T4 levels while parasympathetic innervation derives from branches the the left and also right vagus nerves. Branches that the left and also right phrenic nerves carry out somatic innervation to the fibrous and parietal pericardial layers.<14><1><2><8><9><6><13> Because the boundaries of the middle mediastinum room the borders of the pericardium itself, just a small part of the nerves mentioned truly reside within the middle mediastinum.

The posterior mediastinum includes many autonomic and also somatic nerves. Forgiveness nerves arise native the sorry chain at the T5 to T12 levels and parasympathetic innervation is listed by the left and also right vagus nerves which form of the esophageal plexus. The somatic nerves in the posterior mediastinum are the intercostal nerves.<1><2><8><5>


Muscles

Although frequently overlooked, there are many crucial muscular structures within the thoracic mediastinum. Because that example, the premium thoracic mediastinum consists of the skeletal and also smooth muscle of the esophagus and also the left and right inferior oblique portion of longus colli muscle i beg your pardon assists in mobilizing the cervical spine.<1><3><15> The anterior thoracic mediastinum includes the transversus thoracis muscles, an accessory muscle that expiration. The transversus thoracis muscle originate top top the posterolateral area that the sternum and assist in boring the ribs during active expiration.<16> The center thoracic mediastinum residences one the the most crucial muscles of the body, the heart. The posterior thoracic mediastinum consists of the distal smooth muscular section of the esophagus. Countless of the huge blood vessels in the mediastinum comprise numerous class of smooth muscle that allow for cardiovascular homeostasis.

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Physiologic Variants

Regularly, over there is a minimal level of variation in the compartmentalization and organization the the thoracic mediastinum between individuals. The structures held within the thoracic mediastinal compartments are very subject come variability, though. Below are some physiologic variants the can influence and/or be seen in structures within the thoracic mediastinal compartments.

Superior Mediastinum<17><1><5>:


Absent brachiocephalic stems (right typical carotid and also subclavian arteries branch straight from aortic arch)