Download Middle mediastinum

Subdivisions of mediastinum
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Superior mediastinum
Inferior mediastinum
Anterior mediastinum
Middle mediastinum
Posterior mediastinum
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The mediastinum
Divisions of the mediastinum
There is a plane of division to which the
whole topography (a study or detailed
description of the various features of any
object or entity and the relationships
between them) of the mediastinum can be
related, namely a plane passing
horizontally through the sternal angle of
Louis. This plane passes backwards to the
lower border of the 4th thoracic vertebra.
The superior mediastinum
Borders
The superior mediastinum is wedgeshaped. The anterior boundary is the
manubrium. The posterior boundary is
much longer, due to the obliquity of the
thoracic inlet. It consists of the bodies
of the first four thoracic vertebrae; this
wall is concave towards the
mediastinum.
Superior mediastinum
Locating－from inlet of thorax
to plane extending from level
of sternal angle anteriorly to
lower border of T4 vertebra
posterioly
Contents
Superficial layer •
Thymus –
Three veins –
Left brachiocephelic v. •
Right brachiocephelic v. •
Superior vena cava •
Aortic arch
Continuation of ascending aorta •
Curves upward, to the left and
•
posteriorly, then downward,
arching over left principal
bronchus and pulmonary trunk
to lower border of T4 level, to
become descending aorta
Branches (from right to left ) •
Brachiocephalic trunk－ –
extends to right
sternoclavicular joint,
bifurcates into right
subclavian and right common
carotid arteries
Left common carotid artery –
Left subclavian artery –
Structures at the thoracic inlet
At the thoracic inlet the esophagus lies
against the body of the first thoracic
vertebra. The trachea lies on the
esophagus and itself touches the jugular
notch. These two tubes thus wholly occupy
the midline of the inlet. At the inlet the
apices of the lungs lie laterally, separated
by vessels and nerves passing between the
superior mediastinum and the neck.
Above, between it and the thoracic inlet,
lies the superior mediastinum. Below the
plane, the inferior mediastinum is divided
into three compartments by the fibrous
pericardium: a part in front, the anterior
mediastinum; a part behind, the posterior
mediastinum; and the pericardium itself,
containing the heart and the roots of the
great vessels forming the middle
mediastinum
Contents
The superior mediastinum contains so
many important structures that it is best to
.consider it in stages
Stage 1: the esophagus
The most posterior structure, closely related to
the vertebrae (T1-T4), is the esophagus with the
thoracic duct running up its left side. It is
flattened anteroposteriorly. As it descends, it
inclines slightly towards the left but is pushed
back to the median plane by the arch of the
aorta
Stage 2: the trachea
In front of the upper part of the esophagus
is the trachea, which inclines slightly to the
right and bifurcates at the level of the
manubriosternal joint. Because of tracheal
inclination, the right bronchus is more in
line with the trachea than the left. The
posterior surface of the trachea is flat
where it is applied to the esophagus. It is
kept patent by a series of C-shaped bars of
cartilage.
Between the trachea and esophagus on the
left side is the left recurrent laryngeal
nerve, which comes from the vagus nerve
and hooks under the ligamentum
arteriosum. The arch of the aorta arches
over the root of the left lung; the azygos
vein arches over the root of the right lung.
In front of the tracheal bifurcation is the
pulmonary trunk dividing into left and right
pulmonary arteries. This has the
appearance of a (T) with a sloping
The right pulmonary artery passes to the right lung
behind the ascending aorta, superior vena cava and in
front of the esophagus and right main bronchus. The
left pulmonary artery goes to the left lung in front of
the descending aorta and left main bronchus. The
beginning of the left pulmonary artery is connected to
the under surface of the aorta by the ligamentum
arteriosum, a remnant of the fetal ductus arteriosus
that short-circuited the functionless lungs by
diverging most of the right ventricular outflow into
the aorta. Also in front of the tracheal bifurcation are
the tracheobronchial lymph nodes and the cardiac
plexus.
The barchiocephalic trunk passes superolaterally to
the right side of the trachea and the right
sternoclavicular joint, where it divides into the right
common carotid and right subclavian arteries. The
arch of the aorta passes to the left of the trachea and
esophagus, displacing the trachea to the right and
constricting the esophagus.
The left phrenic nerve crosses the arch of the aorta in
front of the vagus. The left superior intercostal vein
crosses the arch from back to front, over the vagus
and under the phrenic, relationships similar to those
of the azygos vein on the right side, which is
embryologically equivalent to it.
Since the arch is entirely behind the manubrium sterni, the
left brachiocephalic vein is only just below the jugular
(suprasternal) notch and is actually above it in children. The
brachiocephalic veins, which arise posterior to
sternoclavicular joints, unite to form the superior vena cava at
the level of the inferior border of the first right costal
cartilage.
The superior vena cava lies just the right of the ascending
aorta before opening into the right atrium at the level of the
right 3rd costal cartilage. The only other tributary of the
superior vena cava is the azygos vein. The brachiocephalic
veins receive a number of tributaries including the left
superior intercostal vein (into left brachiocephalic)
the inferior thyroid veins which come down from the neck in
front of the trachea, the vertebral veins, and the internal
thoracic veins.
Stage 4: the great veins
In the embryo the venous system is, at first,
symmetrical but cross-connections drain most of the
blood across the midline to the right. In the thorax the
cross-channel is the left brachiocephalic vein. Hence
both superior and inferior venae cavae are on the
right and open into the right atrium.
Each brachiocephalic vein is formed by the junction of
the corresponding subclavian (from the arm, L.
brachium) and internal jugular (from the head, G.
kephale) veins; the left brachiocephalic crosses the
midline just above the arch of the aorta.
Stage 3: the great arteries
The arch of the aorta passes backwards as well as to
the left so that in an antero-posterior x-ray it appears in
an almost end-on view as the aortic knuckle. The
junction between the ascending aorta and the arch is at
the level of the lower border of T4. Thus the whole arch
is in the superior mediastinum. The major branches of
the arch spiral around the trachea and esophagus (at
first anterior then on either side); these are the
brachiocephalic trunk (innominate), the left common
carotid and the left subclavian arteries respectively.
The bronchial arteries to the lungs and the thyroidea ima
artery to the thyroid gland may arise from the aortic arch.
Stage 5: The thymus gland
This important component of the lymphatic system lies
behind the manubrium sterni but may extend up into the
neck or down in the anterior mediastinum. It is molded
around the great vessels and trachea but you may not be able
to recognize it in the dissenting room since in adult life it is
gradually replaced by fat. Because of the deposition of fat
after puberty the pink color of the infant’s thymus changes to
yellow. It reaches its largest size just before puberty but,
relative to the adjacent structures, it appears at its largest
about the time of birth. The rich arterial supply is derived
mainly from the anterior intercostal and branches of the
internal thoracic arteries. The veins end in the left
brachiocephalic, internal thoracic, and inferior thyroid veins.
Notes on the general topography of the superior
mediastinum:
1. The superior mediastinum is in direct continuity
with the anterior and posterior mediastinum and
their separation from it is purely descriptive, not
anatomical.
2. The plane of the sternal angle passes through the
bifurcation of the trachea, the concavity of the arch of
the aorta, and just above the bifurcation of the
pulmonary trunk. On the plane the azygos vein enters
the superior vena cava, the thoracic duct reaches the
left side of the esophagus in its passage upwards from
the abdomen. Also lying in the plane are the
ligamentum arteriosum, and both superficial and
3. The great veins and arteries of the superior
mediastinum are asymmetrical. The veins are on the
right, arteries on the left. Structures themselves
symmetrical, be a midline like trachea or bilateral like
the apices of lungs or the phrenic and vagus nerves,
thus have asymmetrical relationships on the right and
left side. On right side they are in 4. Veins expand
enormously, large arteries not at all, during increased
blood flow. Thus there is much "dead space" on the
right, none on the left, and it is into this space on the
right side that tumors of the mediastinum or liquid
collections tend to project. Contact with veins, on the
left side with arteries.
5. The structures in the mediastinum form the
medial relations of the lungs, being separated
from them by the mediastinal pleura. Some of
them make deep groove on the lungs. The left
lung is intended by the left ventricle of the
heart, the arch of the aorta, the subclavian
artery and the left brachiocephalic vein, and
perhaps lower part of the esophagus. Right lung
carries impressions for the right atrium,
subclavian artery and brachiocephalic vein, the
superior vena cava, the azygos vein and the
esophagus.
Inferior mediastinum
Anterior mediastinum
Location－posterior to
body of sternum and
attached costal cartilages,
anterior to heart and
pericardium
Contents－fat, remnants
of thymus gland, anterior
mediastinal lymph nodes
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The anterior mediastinum
The anterior mediastinum is very narrow and lies
between the body of the sternum anteriorly and
the fibrous pericardium posteriorly. It is
continuous with the superior mediastinum at the
sternal angle. It is limited inferiorly by the
diaphragm.
The anterior mediastinum contains loose areolar
tissue, fat, lymph vessels, two or three lymph
nodes, sternopericardial ligaments, and a few
branches of the internal thoracic artery. In infants
and children, it may also contain the thymus
gland.
Middle layer •
Aotic arch and –
its three
branches
Phrenic n.–
Vagus n.–
Middle mediastinum
Location－between
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anterior mediastinum and
posterior mediastinum
Contents: heart and
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pericardium, beginning or
termination of great
vessels, phrenic nerves,
pericardiacophrenic
vessels , lymph nodes,
The posterior mediastinum
This contains esophagus, the
descending aorta, the azygos venous
system and the thoracic duct. It may be
regarded as a duct leading from the
neck and superior mediastinum to the
abdomen so that all the structures
mentioned above (in addition to the
inferior vena cava) have to pass
through the diaphragm.
Posterior mediastinum
Location－posterior to •
heart and pericardium,
anterior to vertebrae T5－
T12
Contents: esophagus, •
vagus n., thoracic aorta,
azygos system of veins,
thoracic duct, thoracic
sympathetic trunk,
posterior mediastinal
lymph nodes
Posteriorly－posterior •
esophageal plexus,
thoracic aorta, thoracic
duct, azygos v.,
hemiazygos v.,accessory
hemiazygos v., right
posterior intercostal v.
Relations of thoracic aorta
Anteriorly－left root of lung, •
pericardium and esophagus
Posterior－ hemiazygos v., •
accessory hemiazygos v.,
Right－azygos v. and thoracic •
duct
Left－mediastinal pleura •
Mediastinal spaces
Retrosternal space lies •
beween sternum and
endothoracic fascia
Pretracheal space －lies •
within superior mediastinum,
between trachea, bifurcation
of trachea and aortic arch
Retroesophagus space － •
lies within superior
mediastinum, beween
esophagus and endothoracic
fascia
Relations of esophagus
Anteriorly－trachea, •
bifurcation of trachea, left
principal branchus, left
recurrent n., right
pulmonary a., anterior
esophageal plexus,
pericardium, left atrium,
diaphragm
The Mediastinum
Concept－all of organs
between the left and right
mediastinal pleurae is
called mediastinum. It
extends from the sternum
in front to the vertebral
column behind, and from
the thoracic inlet above
to the diaphragm below.
Subdivisions of mediastinum
Superior mediastinum •
Inferior mediastinum •
Anterior mediastinum –
Middle mediastinum –
Posterior mediastinum –
Left side of mediastnum
Left subclavian a.
Thoracic duct
Left vagus n.
Left recurrent n.
Phrenic n. &
pericardiacophrenic a.
Aortic arch
Thoracic aorta
Sympathetic trunk
Root of lung
Pericardium
Esophagus
Greater splanchnic n
Right side of mediastnum
Trachea
Left vagus n.
Arch of azygos v.
Azygos v.
Sympathetic trunk
Esophagus
Inferior vena cava
Superior vena cava
Phrenic n. &
pericardiacophrenic a.
Root of lung
Pericardium
Superior mediastinum
Locating－from inlet of thorax
to plane extending from level
of sternal angle anteriorly to
lower border of T4 vertebra
posterioly
Contents
Superficial layer •
Thymus –
Three veins –
Left brachiocephelic v. •
Right brachiocephelic v. •
Superior vena cava •
Middle layer •
Aotic arch and its three –
branches
Phrenic n. –
Vagus n. –
Posterior layer •
Trachea –
Esophagus –
Thoracic duct –
Relations of aortic arch
Anteriorly and to the left － •
pleura, lung，phrenic n.,
pericardiacophrenic vessels and
vagus n.
Posteriorly and to the right－ •
trachea, esophagus, left recurrent n.,
thoracic duct, deep cardiac plexus
Superiorly－its three branches, left •
brachiocephalic v. and thymus
Inferiorly－pulmonary a., arterial •
ligament, left recurrent n., left
principal bronchus and superficial
cardiac plexus
Inferior mediastinum
Anterior mediastinum
Location－posterior to body of
sternum and attached costal
cartilages, anterior to heart and
pericardium
Contents－fat, remnants of
•
thymus gland, anterior
mediastinal lymph nodes
•
Middle mediastinum
Location－between anterior
mediastinum and posterior
mediastinum
Contents: hart and
•
pericardium, beginning or
termination of great vessels,
phrenic nerves,
pericardiacophrenic vessels ,
lymph nodes,
•
Posterior mediastinum
Location－posterior to heart and
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pericardium, anterior to vertebrae
T5－T12
Contents: esophagus, vagus n.,
•
thoracic aorta, azygos system of
veins, thoracic duct, thoracic
sympathetic trunk, posterior
mediastinal lymph nodes
Relations of esophagus
Anteriorly－trachea, bifurcation
of trachea, left principal
branchus, left recurrent n., right
pulmonary a., anterior
esophageal plexus, pericardium,
left atrium, diaphragm
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Left－left common carotid a., left subclavian a., aortic arch,
thoracic aorta, superior part of thoracic duct
Right－arch of azygos v. •
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Mediastinal spaces
Retrosternal space －lies beween •
sternum and endothoracic fascia
Pretracheal space －lies within •
superior mediastinum, between
trachea, bifurcation of trachea and
aortic arch
Retroesophagus space － lies •
within superior mediastinum,
beween esophagus and
endothoracic fascia