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
lungs 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: • The
superior mediastinum starts at the
superior thoracic aperture and ends at the
thoracic plane. • 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.
Anatomists,
surgeons, 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. 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.
Superior mediastinum 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 • 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
Inferior mediastinum Anterior inferior 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. ;Contents • A quantity of
loose areolar tissue • Some
lymphatic vessels which ascend from the convex surface of the
liver • Two or three anterior mediastinal
lymph nodes • The small
mediastinal branches of the
internal thoracic artery •
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 • 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 • pericardiacophrenic vessels
Posterior inferior 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); • Laterally by the
mediastinal pleura (on either side). • artery •
thoracic part of the
descending aorta • veins •
azygos vein • the
hemiazygos vein and the
accessory hemiazygos vein • nerves •
vagus nerve •
splanchnic nerves •
sympathetic chain •
esophagus •
thoracic duct • some
lymph glands File:Gray968.png |A transverse section of the
thorax, showing the contents of the
middle and the
posterior mediastinum. == Clinical significance ==