INTRODUCTION TO MEDIASTINUM &
SUPERIOR MEDIASTINUM
LEARNING OBJECTIVES
At the end of this lecture you will be able to
describe
• Mediastinum
• Boundaries & contents of Mediastinum
• Division of Mediastinum
• Superior mediastinum
• Boundaries & contents of Superior mediastinum
• Overview of Inferior mediastinum
Mediastinum
Mediastinum is the middle space left in the thoracic cavity in
between the lungs.
• It is covered on each side by mediastinal pleura and contains
all the thoracic viscera and structures except the lungs.
• EXTENT: The mediastinum extends 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.
• The major structures in the mediastinum are surrounded by
blood and lymphatic vessels, lymph nodes, nerves, and fat.
MEDIASTINUM..
Boundaries
• Anteriorly: Sternum
• Posteriorly: Vertebral column
• Superiorly: Thoracic inlet
• Inferiorly: Diaphragm
• On each side: Mediastinal pleura.
MEDIASTINUM..
Divisions
• the mediastinum is divided into the superior mediastinum and the
inferior mediastinum.
• The inferior mediastinum is further divided into the anterior, middle and
posterior mediastina
• The superior mediastinum is separated from the inferior by an imaginary
plane passing through the sternal angle anteriorly and the lower border
of the body of the fourth thoracic vertebra posteriorly.
• The inferior mediastinum is subdivided into three parts by the
pericardium.
• The area in front of the pericardium is the anterior mediastinum.
• The area behind the pericardium is the posterior mediastinum.
• The pericardium and its contents form the middle mediastinum.
DIVISIONS
• The superior mediastinum extends inferiorly from the superior
thoracic aperture to the horizontal plane that includes the sternal
angle anteriorly and passes approximately through the junction (IV
disc) of T4 and T5 vertebrae posteriorly, often referred to as the
transverse thoracic plane.
• The inferior mediastinum—between the transverse thoracic plane
and the diaphragm
—is further subdivided by the pericardium into anterior, middle,
and posterior parts. The pericardium and its contents (heart and roots
of its great vessels) constitute the middle mediastinum. Some
structures, such as the esophagus, pass vertically through the
mediastinum and therefore lie in more than one mediastinal
compartment.
A). SUPERIOR MEDIASTINUM
SUPERIOR MEDIASTINUM
Boundaries
• Anteriorly: Manubrium sterni
• Posteriorly: Upper four thoracic vertebrae
• Superiorly: Plane of the thoracic inlet
• Inferiorly: An imaginary plane passing through the
sternal angle in front, and the lower border of the
body of the fourth thoracic vertebra behind.
• On each side: Mediastinal pleura.
Contents
• 1 Trachea and oesophagus
• 2 Muscles: Origins of (i) sternohyoid, (ii) sternothyroid,(iii) lower
ends of longus colli.
• 3 Arteries: (i) Arch of aorta, (ii) brachiocephalic artery,(iii) left
common carotid artery, (iv) left subclavian artery
• 4 Veins: (i) Right and left brachiocephalic veins,(ii) upper half of the
superior vena cava, (iii) left superior intercostal vein.
• 5 Nerves: (i) Vagus, (ii) phrenic, (iii) cardiac nerves of both sides,
(iv) left recurrent laryngeal nerve.
• 6 Thymus
• 7 Thoracic duct
• 8 Lymph nodes: Paratracheal, brachiocephalic, and
tracheobronchial.
INFERIOR MEDIASTINUM
The inferior mediastinum is divided into—anterior, middle and posterior mediastina.
A). Anterior Mediastinum
• It is continuous through the superior mediastinum with the pretracheal space of the neck. It
contains areolar tissue and part of thymus gland.
Boundaries
• Anteriorly: Body of sternum
• Posteriorly: Pericardium
• Superiorly: Imaginary plane separating the superior mediastinum from the inferior mediastinum.
• Inferiorly: Superior surface of diaphragm
• On each side: Mediastinal pleura
Contents
• 1 Sternopericardial ligaments
• 2 Lymph nodes with lymphatics
• 3 Small mediastinal branches of the internal thoracic artery
• 4 The lowest part of the thymus
• 5 Areolar tissue.
B). Middle Mediastinum
• Middle mediastinum is occupied by the pericardium and its contents, along with
the phrenic nerves and the pericardiacophrenic vessels.
Boundaries
• Anteriorly: Sternopericardial ligaments
• Posteriorly: Oesophagus, descending thoracic aorta, azygos vein
• On each side: Mediastinal pleura
Contents
• 1 Heart enclosed in pericardium
• 2 Arteries: (i) Ascending aorta, (ii) pulmonary trunk, (iii) two pulmonary arteries
• 3 Veins: (i) Lower half of the superior vena cava, (ii) terminal part of the azygos
vein, and (iii) right and left pulmonary veins.
• 4 Nerves: (i) Phrenic, and (ii) deep cardiac plexus.
• 5 Lymph nodes: Tracheobronchial nodes.
C). Posterior Mediastinum
Boundaries
• Anteriorly: (i) Pericardium, (ii) bifurcation of trachea, (iii) pulmonary
vessels, and (iv) posterior part of the upper surface of the diaphragm.
• Posteriorly: Lower eight thoracic vertebrae and intervening discs.
• On each side: Mediastinal pleura.
Contents
• 1 Oesophagus
• 2 Arteries: Descending thoracic aorta and its branches.
• 3 Veins: (i) Azygos vein, (ii) hemiazygos vein, and (iii) accessory
hemiazygos vein.
• 4 Nerves: (i) Vagi, (ii) splanchnic nerves, greater, lesser and least,
arising from the lower eight thoracic ganglia of the sympathetic chain
• 5 Lymph nodes and lymphatics:
a. Posterior mediastinal lymph nodes lying
alongside the aorta. b. The thoracic duct
MEDIASTINAL SYNDROME
•
Compression of mediastinal structures by any tumour gives rise to a group of
symptoms known as mediastinal syndrome.
• The common symptoms are as follows:
• A. Obstruction of superior vena cava gives rise to engorgement of veins in the
upper half of the body.
• b. Pressure over the trachea causes dyspnoea, and cough.
• c. Pressure on oesophagus causes dysphagia.
• d.Pressure or the left recurrent laryngeal nerve gives rise to hoarseness of voice
(dysphonia).
• e. Pressure on the phrenic nerve causes paralysis of the diaphragm on that side.
• f.Pressure on the intercostal nerves gives rise to pain in the area supplied by them.
It is called intercostal neuralgia.
• g. Pressure on the vertebral column may cause erosion of the vertebral bodies.
The common causes of mediastinal syndrome are bronchogenic carcinoma, Hodgkin’s
disease causing enlargement of the mediastinal lymph nodes, aneurysm or dilatation
of the aorta, etc.
MEDIASTINITIS
• The prevertebral layer of the deep cervical fascia extends to
the superior mediastinum, and is attached to the fourth
thoracic vertebra. An infection present in the neck behind
this fascia can pass down into the superior mediastinum but
not lower down.
• The pretracheal fascia of the neck also extends to the
superior mediastinum, where it blends with the arch of the
aorta. Neck infections between the pretracheal and
prevertebral fasciae can spread into the superior
mediastinum, and through it into the posterior mediastinum.
Thus mediastinitis can result from infections in the neck.
• THANK YOU