Divided into the anterior, middle and posterior compartments.
No tissue plane exists separating these compartments.
Lateral chest x-ray indicate that the anterior and middle compartments are separated by a line anterior to the trachea and posterior to the inferior vena cava.
The middle and posterior compartments are separated by a line passing 1 cm posteriorly to the anterior border of the vertebral body.
The division between superior and inferior mediastinum is at the sternal angle.
It lies within the thorax and is enclosed on the right and left by pleurae.
The mediastinum 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 at its back.
The M contains all the organs of the thorax except the lungs, and is continuous with the loose connective tissue of the neck.
It can be divided into an upper, superior, and lower or inferior part.
The superior mediastinum starts at the superior thoracic aperture and ends at the thoracic plane.
The inferior mediastinum ranges from the thoracic aperture to the diaphragm.
The inferior mediastinum is subdivided into three regions, in relation 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.
The transverse thoracic plane is at the level of the sternal angle and the T4/T5 intervertebral disc.
The transverse thoracic plane is an imaginary boundary that separates the superior and inferior mediastinum.
Anatomical structures and transitions at the level of the thoracic plane, include:
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 upper opening of the thorax
Inferiorly by the transverse thoracic plane.
The anterior mediastinum
Is bounded:
laterally by the pleurae;
posteriorly by the pericardium;
anteriorly by the sternum ,
the left transversus thoracis and the fifth, sixth, and seventh left costal cartilages.
The contents of the anterior M includes:
loose areolar tissue, lymphatic vessels from the surface of the liver, mediastinal lymph nodes, branches of the internal thoracic artery, the thymus,
superior and inferior sternopericardial ligaments.
Middle mediastinum is bounded by the pericardial sac.
The middle mediastinum contains:
the heart enclosed in the pericardium
the ascending aorta
the lower half of the superior vena cava with the azygos vein opening into it
the bifurcation of the trachea and the two bronchi
the pulmonary trunk dividing into its two branches
the right and left pulmonary veins
the phrenic nerves
some bronchial lymphatic glands
pericardiocophrenic vessels
Posterior mediastinum
Is bounded:
Anteriorly by the bifurcation of trachea; pulmonary vessels; fibrous pericardium and posterior sloping surface of diaphragm
Inferiorly by the thoracic surface of the diaphragm.
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.
Laterally by the mediastinal pleura.
Contents of posterior mediastinum:
thoracic part of the descending aorta
azygos vein
the hemiazygos vein and the accessory hemiazygos vein
vagus nerve
splanchnic nerves
sympathetic chain
esophagus
thoracic duct
lymph glands
Mediastinal adenopathy is frequently an indication of involvement of various tumors.
Anterior mediastinum: substernal thyroid goiters, lymphoma, thymoma, and teratoma.
Middle mediastinum: lymphadenopathy, metastatic disease from carcinoma from the lung.
Posterior mediastinum: Neurogenic tumors, either from the nerve sheath which is mostly benign or malignant lesions.
Mediastinitis refers to inflammation of the tissues in the mediastinum, usually bacterial..
Mediastinitis is due to rupture of organs in the mediastinum.
Pneumomediastinum refers to the presence of air in the mediastinum, which in some cases can lead to pneumothorax, pneumoperitoneum, and pneumopericardium.
Pneumomediastinum may accompany Boerhaave syndrome, or spontaneous esophageal rupture.
Widened mediastinum 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.
A widened mediastinum digests:
aortic aneurysm
aortic dissection
aortic unfolding
aortic rupture
hilar lymphadenopathy
anthrax inhalation
esophageal rupture
mediastinal mass
cardiac tamponade
pericardial effusion
thoracic vertebrae fractures in trauma patients.