The mediastinum is an undelineated group of structures in the thorax, surrounded by loose
connective tissue.
It is the central compartment of the thoracic cavity.
It contains the heart, the great vessels of the heart, the esophagus, the trachea, the
phrenic nerve, the cardiac nerve, the thoracic duct, the thymus, and the lymph nodes of the
central chest.
Structure The mediastinum lies between the right and
left pleurae in and near the median sagittal plane of the chest.
It extends from the sternum in front to the vertebral column behind, and contains all
the thoracic viscera except the lungs.
It may be divided for purposes of description into two parts: an upper or superior part
and a lower or inferior part.
The superior mediastinum extends from the upper level of the pericardium with its upper
limit at the superior thoracic aperture and its lower limit at the thoracic plane which
runs from the sternal angle to the intervertebral disc of T4-T5.
The thoracic plane divides the mediastinum into these upper and lower parts.
The inferior mediastinum extends below the upper level of the pericardium onto the diaphragm.
This lower part is subdivided into three regions all relative to the pericardium.
The anterior mediastinum is in front of the pericardium.
The middle mediastinum contains the pericardium and its contents.
The posterior mediastinum is behind the pericardium.
It is surrounded by the chest wall in front, the lungs to the sides and the spine at the
back.
It is continuous with the loose connective tissue of the neck.
Anatomists, surgeons, and clinical radiologists compartmentalize the mediastinum differently.
For instance, in the radiological scheme of Felson, there are only three compartments,
and the heart is part of the anterior mediastinum.
Significant findings at the level of the thoracic plane
1.
The start and end of the aortic arch 2.
The upper margin of the superior vena cava 3.
The crossing of the thoracic duct 4.
The bifurcation of the trachea 5.
The bifurcation of the pulmonary trunk 6.
The level of the sternal angle 7.
The level of Rib 2 where it attaches to the sternum via the 2nd costal cartilage
8.
The body of vertebrae T4 9.
The drainage of the azygos vein into the superior vena cava
Contents Clinical significance
The mediastinum is frequently the site of involvement of various tumors:
Anterior mediastinum: substernal thyroid goiters, lymphoma, thymoma and teratoma.
Middle mediastinum: lymphadenopathy, metastatic disease such as from small cell carcinoma
from the lung.
Posterior mediastinum: Neurogenic tumors, either from the nerve sheath or elsewhence.
Mediastinitis is inflammation of the tissues in the mediastinum, usually bacterial 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's syndrome, or spontaneous esophageal rupture.
There are many diseases that can present with a widened mediastinum.
The most common ones are aortic unfolding, traumatic aortic rupture, thoracic aortic
aneurysm, and traumatic thoracic vertebral fracture.
With infectious etiologies, a widened mediastinum is a classic hallmark sign of anthrax infection.
See also Widened mediastinum
Mediastinum testis Mediastinal germ cell tumor
Mediastinitis Anthrax
Mediastinal tumor References
This article incorporates text from a public domain edition of Gray's Anatomy.
Additional images
External links 1691353147 at GPnotebook
Anatomy figure: 21:01-03 at Human Anatomy Online, SUNY Downstate Medical Center - "Divisions
of the mediastinum."
Anatomy figure: 21:02-03 at Human Anatomy Online, SUNY Downstate Medical Center - "The
anatomical divisions of the inferior mediastinum."
thoraxlesson3 at The Anatomy Lesson by Wesley Norman - "Subdivisions of the Thoracic Cavity"
mediastinum at eMedicine Dictionary Anatomy at MUN thorax/media