Behind the body and xiphoid process of the sternum
and in front of the middle mediastinum
Boundaries
Anterior : the body of the sternum.
Posterior : middle mediastinum (the pericardium)
On each side : the mediastinal layer of pleura.
Contents
Superior and inferior sternopericardial ligaments.
Part of the thymus gland
Important component of the lymphatic system.
Lies behind the manubrium sterni & may extend up
into the neck or down in the anterior mediastinum.
It appears large at time of birth, gradually replaced
by fat in adult life.
Internal mammary artery
Two to three lymph nodes and lymphatics.
Sternocostalis muscle. (part of transversus
thoracis muscles)
Areolar tissue.
Middle
Meiastinum
Is the part of the inferior mediastinum that is
occupied by the pericardium and its contents.
Boundaries
Superiorly: the imaginary horizontal plane
Inferiorly: diaphragm.
Anteriorly: anterior mediastinum.
Posteriorly: posterior mediastinum
Contents
The pericardium and the heart.
Ascending aorta
The pulmonary trunk
The lower half of the SVC
The upper most part of the IVC
The four pulmonary veins.
Bifurcation of pulmonary trunk into
right and left pulmonary arteries.
Bifurcation of the trachea.
The right and left phrenic nerves: along the sides of the pericardium.
Inferior tracheobronchial lymph nodes: below the bifurcation of the trachea.
Posterior
Mediastinum
Between the pericardium and the vertebral column
Boundaries
Superiorly: the imaginary horizontal plane
Inferiorly: diaphragm.
Anteriorly: the pericardium above , and the diaphragm below.
Posteriorly: the lower 8 thoracic vertebrae (from the 5th to the 12th).
Contents
Descending thoracic aorta.
(the aorta is ascending in the middle
mediastinum, arch in the superior, and
descending in the posterior)
Esophagus: on the right side of
the aorta, then crosses in front
of its lower part
This is why the aortic opening of the diagram is the most
posterior (level of T12), while the one anterior to it is the
esophageal (level of T10) – vena cava opening is at T8)
Azygos and hemiazygos veins.
The two vagi nerves:
The right vagus >> posterior gastric nerve
the left vagus >> anterior gastric nerve (due to the rotation of
the stomach during the development of the GIT)
The splanchnic nerves (greater, lesser and lowest splanchnic
nerves): they arise from the sympathetic trunk.
The thoracic duct: ascends on the right side of the esophagus
till the level of the sternal angle where it becomes on the left
side of the esophagus.