The mediastinum (from ) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is an undelineated region that contains a group of structures within the thorax, namely the heart and its vessels, the esophagus, the trachea, the phrenic and cardiac nerves, the thoracic duct, the thymus and the lymph nodes of the central chest. Anatomy The mediastinum lies within the thorax and is enclosed on the right and left by pleurae. It is surrounded by the chest wall in front, the lungs to the sides and the spine at the back. It extends from the sternum in front to the vertebral column behind. It contains all the organs of the thorax except the lungs. It is continuous with the loose connective tissue of the neck. The mediastinum can be divided into an upper (or superior) and lower (or inferior) part: The superior mediastinum starts at the superior thoracic aperture and ends at the thoracic plane. The inferior mediastinum from this level to the diaphragm. This lower part is subdivided into three regions, all relative to the pericardium – the anterior mediastinum being in front of the pericardium, the middle mediastinum contains the pericardium and its contents, and the posterior mediastinum being behind the pericardium. Anatomists, surgeons, and clinical radiologists compartmentalize the mediastinum differently. For instance, in the radiological scheme of Felson, there are only three compartments (anterior, middle, and posterior), and the heart is part of the middle (inferior) mediastinum. Thoracic plane The transverse thoracic plane, thoracic plane, plane of Louis or plane of Ludwig is an important anatomical plane at the level of the sternal angle and the T4/T5 intervertebral disc. It serves as an imaginary boundary that separates the superior and inferior mediastinum. A number of important anatomical structures and transitions occur at the level of the thoracic plane, including: The carinal bifurcation of the trachea into the left and right main bronchi. The left recurrent laryngeal nerve branching off the left vagus nerve and hooking under the ligamentum arteriosum between the aortic arch above and the pulmonary trunk below. The starting of the cardiac plexus. The azygos vein arching over the right main bronchus and joining into the superior vena cava. The thoracic duct crossing the midline from right to left behind the esophagus The end of the pretracheal and prevertebral fasciae. Superior mediastinum The superior mediastinum is bounded: superiorly by the