The mediastinum (from ;
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
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:
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The superior mediastinum starts at the superior thoracic aperture and ends at the thoracic plane.
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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.
, , 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:
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The carinal bifurcation of the trachea into the left and right main bronchi.
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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.
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The starting of the cardiac plexus.
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The azygos vein arching over the right main bronchus and joining into the superior vena cava.
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The thoracic duct crossing the midline from right to left behind the esophagus
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The end of the pretracheal and prevertebral fasciae.
Superior mediastinum
The superior mediastinum is bounded:
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superiorly by the thoracic inlet, the upper opening of the thorax;
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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;
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laterally by the pleurae;
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anteriorly by the manubrium of the sternum;
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posteriorly by the first four thoracic vertebral bodies.
- Contents
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muscles
-
arteries
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aortic arch
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brachiocephalic artery
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thoracic portions of the left common carotid and the left subclavian
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veins
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brachiocephalic veins and
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upper half of the superior vena cava
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left highest intercostal vein
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nerves
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trachea with paratracheal and tracheobronchial lymph nodes
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esophagus
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thoracic duct
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remains of the thymus
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some lymph glands
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anterior longitudinal ligament
Inferior mediastinum
Anterior inferior mediastinum
Is bounded:
-
laterally by the pleurae;
-
posteriorly by the pericardium;
-
anteriorly by the Human sternum,
- Contents
-
A quantity of loose areolar tissue
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Some lymphatic vessels which ascend from the convex surface of the liver
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Two or three anterior mediastinal lymph nodes
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The small mediastinal branches of the internal thoracic artery
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Thymus (involuted in adults)
-
superior and inferior sternopericardial ligaments
Middle inferior mediastinum
Bounded:
pericardial sac – It contains the vital organs and is classified into the serous and fibrous pericardium.
- Contents
Posterior inferior mediastinum
Is bounded:
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Anteriorly by (from above downwards): bifurcation of trachea; pulmonary vessels; fibrous pericardium and posterior sloping surface of diaphragm
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Inferiorly by the thoracic surface of the diaphragm (below);
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Superiorly by the transverse thoracic plane;
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Posteriorly by the bodies of the vertebral column from the lower border of the fifth to the twelfth thoracic vertebra (behind);
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Laterally by the mediastinal pleura (on either side).
, showing the contents of the middle and the posterior mediastinum.]]
Clinical significance
The mediastinum is frequently the site of involvement of various tumors:
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Anterior mediastinum: substernal Thyroid gland , lymphoma, thymoma, and teratoma.
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Middle mediastinum: lymphadenopathy, metastatic disease such as from small cell carcinoma from the lung.
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Posterior mediastinum: Neurogenic tumors, either from the nerve sheath (mostly benign) or elsewhere (mostly malignant).
Mediastinitis is inflammation of the tissues in the mediastinum, usually and due to rupture of organs in the mediastinum. As the infection can progress very quickly, this is a serious condition.
Pneumomediastinum is the presence of air in the mediastinum, which in some cases can lead to pneumothorax, pneumoperitoneum, and pneumopericardium if left untreated. However, that does not always occur and sometimes those conditions are actually the cause, not the result, of pneumomediastinum. These conditions frequently accompany Boerhaave syndrome, or spontaneous Esophagus rupture.
Widening
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.
A widened mediastinum can be indicative of several pathologies:
See also
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Mediastinum testis (unrelated structure in the scrotum)
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Mediastinal germ cell tumor
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Mediastinitis
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Mediastinal tumor
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List of anatomy mnemonics#Mediastinum
External links
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– "Divisions of the mediastinum."
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– "The anatomical divisions of the inferior mediastinum."
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– "Subdivisions of the Thoracic Cavity"
