The mediastinum is the central compartment of the thoracic cavity located between the two lungs. It contains the heart, major blood vessels, esophagus, trachea, thymus and lymph nodes. The mediastinum is divided into superior and inferior portions by the transverse thoracic plane. The superior mediastinum contains the thymus, great vessels, trachea and esophagus. The inferior mediastinum is divided into anterior, middle and posterior portions by the heart and pericardium.

1. Mediastinum
• It is the middle part of the thoracic cavity found
between the two mediastinal pleurae of the right and
left pleural sacs.
• Occupied by the mass of tissue between the two
pulmonary cavities.
• Is the central compartment of the thoracic cavity
which is covered on each side by the mediastinal
pleura and contains all the thoracic viscera and
structures except the lungs.
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3. Mediastinum
• The mediastinum extends superiorly from the
superior thoracic aperture to the diaphragm inferiorly
and from the sternum and costal cartilages anteriorly
to the bodies of the thoracic vertebrae posteriorly.
• It is divided into superior and inferior by an imaginary
line passing through the sternal angle and the
bifurcation of the trachea to the lower border of the
body of the T4 (or IV disc between the T4 and T5.
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4. SUBDIVISION OF Mediastinum
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5. Mediastinum
• The inferior
mediastinum
– lies between the
transverse thoracic
plane and the
diaphragm
–is further subdivided by
the pericardium and
heart into anterior,
middle and posterior
parts .
• The superior mediastinum
extends from the superior
thoracic aperture to the
horizontal plane that passes
through sternal angle
anteriorly and through the
junction (IV disc) of the T4
and T5 vertebrae posteriorly
,often referred to as
transverse thoracic plane .
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7. Boundaries of Mediastinum
 Anterior - sternum and costal cartilages with the
endothoracic fascia
• Posterior - anterior surfaces of the bodies of the
thoracic vertebrae
• Inferior - Diaphragm
• Superior - Thoracic inlet
• Lateral - Mediastinal pleurae with hila of the lungs.
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8. Communications of the mediastinum
• The mediastinum
communicates:
1. Superiorly with the
neck through the
superior thoracic
aperture - this
communication allows
the passage of the
following structures
into and out of the
mediastinum.
a. Trachea
b. Oesophagus
c. Arteries and veins of the
head, neck and arm
d. Lymphatic vessels including
the thoracic duct
e. Nerves like the phrenic
nerve, vagus and branches
of the sympathetic trunk.
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10. Communications of the mediastinum
2. Laterally with the hila
of the lungs - where the
Principal (primary) and
secondary (lobar)
bronchi, pulmonary
arteries and veins,
bronchial vessels,
bronchopulmonary
lymph nodes and
autonomic pulmonary
nerve plexuses are
found.
• 3. Inferiorly with the
diaphragm through the
openings of the diaphragm,
mainly through the vena
caval foramen, oesophageal
hiatus and aortic hiatus.
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12. Superior mediastinum
• The superior mediastinum is superior to the
transverse thoracic plane .
• The contents of superior mediastinum from anterior
to posterior are ;
thymus,
great vessels, with the veins (brachiocephalic veins
and svc ) anterior to the arteries(arch of the aorta and
the roots of its major branches –the brachiocephalic
trunk ,left common carotid artery ,and left sub clavian
artery) and related nerves (vagus and phrenic nerves
and the cardiiac plexus of nerves.
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14. Superior mediastinum
Inferior continuation of
the cervical viscera
(trachea anteriorly and
esophagus posteriorly)
and related nerves (left
recurrent laryngeal
nerve).
Thoracic duct and
lymphatic trunks .
To summarise systemically,
the major structures in the
superior mediastinum, from
anterior to posterior are: -
Thymus,
veins,
arteries,
airway,
alimentary tract, and
lymphatic trunks
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16. Anterior mediastinum
• is the part ventral to the pericardium and dorsal to
the sternum and costal cartilages.
• lies between the body of the sternum anteriorly and
the pericardium posteriorly.
• is the smallest sub division of the mediastinum
it is continuous with the superior mediastinum at the
sternal angle and limited inferiorly by the diaphragm.
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17. Anterior mediastinum
It is mainly filled with connective tissue but also
contains:-
The parasternal lymph nodes and lymphatic vessels
Internal thoracic vessels
Sternopericardial ligament
In some cases part of the thymus.
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18. Posterior mediastinum
• the posterior part of the inferior mediastinum
• is located inferior to the transverse thoracic plane
,anterior to the T5 –T12 vertebrae, posterior to
pericardium and between the parietal pleura of the
two lungs.
• is found behind the pericardium but in front of the
bodies of the thoracic vertebrae.
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19. Posterior mediastinum
Contents:
Oesophagus
Vagus nerves
Greater and lesser splanchnic nerves
Thoracic aorta
Azygos and hemiazygos veins
 Thoracic duct
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20. Middle mediastinum
• Middle mediastinum is the part occupied by the heart
and pericardium
• It includes the pericardium ,heart and the roots of its
great vessels-ascending aorta,pulmonary trunk and
svc-passing to and from the heart
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21. Middle mediastinum
Contents:
Pericardium and the heart
Phrenic nerves
Pulmonary trunk
Pulmonary veins
Ascending aorta
Superior vena cava
Inferior vena cava
Pericardiacophrenic vessels
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