 Superior mediastinum  Inferior mediastinum  A. Anterior  B. Middle  C. Posterior

 superior mediastinum: [Green]  Inferior Mediastinum: Below the plane passing from Sternal Angle/Angle Luise  Inferior mediastinum has 3 parts:  Purple: anterior mediastinum;  Yellow: middle mediastinum;  Blue: posterior mediastinum

 The superior mediastinum is posterior to the manubrium of the sternum and anterior to the bodies of the first four thoracic vertebrae.  The superior mediastinum is continuous with the neck superiorly and with the inferior mediastinum inferiorly.

 From Posterior to anterior  Layer 1: Esophagus  Layer 2: Trachea  Layer 3: Arch of the aorta with its three large branches  Layer 4: Right and left brachiocephalic veins, Superior vena cava  Layer 5: Thymus

 Thymus  Right and left brachiocephalic veins  Left superior intercostal vein  Superior vena cava  Arch of the aorta with its three large branches  Trachea  Esophagus

 Phrenic nerves  Vagus nerves  Left recurrent laryngeal branch of the left vagus nerve  Thoracic duct

 The vertically oriented superior vena cava begins posterior to the lower edge of the right first costal cartilage, where the right and left brachiocephalic veins join, and terminates at the lower edge of the right third costal cartilage, where it joins the right atrium.  The superior vena cava receives the azygos vein immediately before entering the pericardial sac

 Only the arch of the aorta is in the superior mediastinum.  It begins when the ascending aorta emerges from the pericardial sac and courses upward, backward, and to the left as it passes through the superior mediastinum, ending on the left side at vertebral level TIV/V.

 The trachea is a midline structure that is palpable in the jugular notch as it enters the superior mediastinum.  Posterior to it is the esophagus, which is immediately anterior to the vertebral column.

 The left vagus nerve also gives rise to the left recurrent laryngeal nerve, which arises from it at the inferior margin of the arch of aorta just lateral to the ligamentum arteriosum.  Entering a groove between the trachea and esophagus, the left recurrent laryngeal nerve continues superiorly to enter the neck and terminate in the larynx.

 The posterior mediastinum is posterior to the pericardial sac and diaphragm and anterior to the bodies of the mid and lower thoracic vertebrae

 Esophagus and its associated nerve plexus  Thoracic aorta and its branches  Azygos system of veins  Thoracic duct and associated lymph nodes  Sympathetic trunks  Thoracic splanchnic nerves

 Relationships to important structures in the posterior mediastinum  1. Posterior to the esophagus, the thoracic duct is on the right side inferiorly, but crosses to the left more superiorly.  2. Esophagus passes immediately posteriorly to the left atrium, separated from it only by pericardium

 The thoracic portion of the descending aorta (thoracic aorta) begins at the lower edge of vertebra TIV.  Branches of the thoracic aorta  1. Pericardial branches  2. Bronchial branches  3. Esophageal branches  4. Posterior intercostal arteries  5. Superior phrenic arteries  6. Subcostal artery

 The azygos vein arises opposite vertebra LI or LII at the junction between the right ascending lumbar vein and the right subcostal vein.  The azygos vein enters the thorax through the aortic hiatus of the diaphragm.  At approximately vertebral level TIV, it arches anteriorly, over the root of the right lung, to join the superior vena cava

 The thoracic duct is the principal channel through which lymph from most of the body is returned to the venous system.  It begins as a confluence of lymph trunks in the abdomen, sometimes forming a saccular dilation referred to as the cisterna chyli (chyle cistern), which drains the abdominal viscera and walls, pelvis, perineum, and lower limbs.  Thoracic duct empties into the junction of the left subclavian and left internal jugular veins.

 Sympathetic trunks consists of two parallel cords punctuated by 11 or 12 ganglia.  Thoracic splanchnic nerves  1. Greater splanchnic nerve  2. Lesser splanchnic nerve  3. Least splanchnic nerve (lowest splanchnic nerve)

 The anterior mediastinum is posterior to the body of the sternum and anterior to the pericardial sac  CONTENTS:  Sterno paricardial ligaments  Few lymph nodes  Branches of the internal thoracic vessels.  In infants and children, the anterior mediastinum contains the inferior part of the thymus.