Mediastinum

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.[8][9][10] It serves as an imaginary boundary that separates the superior and inferior mediastinum.[8][9][10]

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.

The superior mediastinum is bounded:

• superiorly by the thoracic inlet, the upper opening of the thorax;
• inferiorly by the transverse thoracic plane. which is an imaginary plane passing from the sternal angle anteriorly to the lower border of the body of the 4th thoracic vertebra posteriorly;
• laterally by the pleurae;
• anteriorly by the manubrium of the sternum;
• posteriorly by the first four thoracic vertebral bodies.

Contents

Mediastinum anatomy. Some mediastinal structures on a chest radiograph. Contents muscles origins of the Sternohyoidei and Sternothyreoidei lower ends of the Longi colli arteries aortic arch brachiocephalic artery thoracic portions of the left common carotid and the left subclavian veins brachiocephalic veins and upper half of the superior vena cava left highest intercostal vein nerves vagus nerve cardiac nerve superficial and deep cardiac plexuses phrenic nerve left recurrent laryngeal nerve trachea with paratracheal and tracheobronchial lymph nodes esophagus thoracic duct remains of the thymus some lymph glands anterior longitudinal ligament

Anterior mediastinum

Is bounded:

• laterally by the pleurae;
• posteriorly by the pericardium;[4]
• anteriorly by the sternum ,[4] the left transversus thoracis and the fifth, sixth, and seventh left costal cartilages.

Middle mediastinum

Bounded: pericardial sac – It contains the vital organs and is classified into the serous and fibrous pericardium.[4]

Posterior mediastinum

Is bounded:

• Anteriorly by (from above downwards): bifurcation of trachea; pulmonary vessels; fibrous pericardium and posterior sloping surface of diaphragm
• Inferiorly by the thoracic surface of the diaphragm (below);
• Superiorly by the transverse thoracic plane;
• Posteriorly by the bodies of the vertebral column from the lower border of the fifth to the twelfth thoracic vertebra (behind);[4]
• Laterally by the mediastinal pleura (on either side).

• 
  A transverse section of the thorax, showing the contents of the middle and the posterior mediastinum.

Widened mediastinum
Other names	Mediastinal widening
Widened mediastinum in a patient with achalasia

Widened mediastinum/mediastinal widening is where the mediastinum has a width greater than 6 cm on an upright PA chest X-ray or 8 cm on supine AP chest film.[11]

A widened mediastinum can be indicative of several pathologies:[12][13]

• aortic aneurysm[14]
• aortic dissection[15]
• aortic unfolding
• aortic rupture
• hilar lymphadenopathy
• anthrax inhalation - a widened mediastinum was found in 7 of the first 10 victims infected by anthrax (Bacillus anthracis) in 2001.[16]
• esophageal rupture - presents usually with pneumomediastinum and pleural effusion. It is diagnosed with water-soluble swallowed contrast.
• mediastinal mass
• mediastinitis
• cardiac tamponade[17]
• pericardial effusion
• thoracic vertebrae fractures in trauma patients.