Superior and inferior mediastinum

Superior & Inferior
Mediastinum
Moamer Gabsa
BDS,diploma of research method
,MSc Anatomy
Moamer Gabsa

By the end of this lecture any one can be able to identify:
• Boundaries of mediastinum
• Divisions of mediastinum
• Content of superior mediastinum
• Content of inferior mediastinum
Objectives

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• The mediastinum (L. middle septum)
occupied by the mass of tissue between
the two pulmonary cavities is the central
compartment of the thoracic cavity.
• It is covered on each side by mediastinal
pleura and contains all the thoracic
viscera and structures except the lungs.
The mediastinum

• Superiorly : Superior thoracic aperture
(thoracic inlet) & Root of the neck
• Inferiorly : Diaphragm
• Anteriorly : Sternum
• Posteriorly : Thoracic vertebrae (T2-9)
• Laterally : Right and left pleural cavity

The mediastinum is artificially divided
into:
• Superior
• Inferior
for purposes of description by
transverse thoracic plane (line).
This plane from Sternal angle (angle of
Louis or manbriosternal joint) anteriorly
To Lower border of T4 posteriorly

• Superior mediastinum extend from
superior thoracic aperture (thoracic inlet)
superiorly to transverse thoracic plane
inferiorly
• The inferior mediastinum extend
from the transverse plane superiorly to
diaphragm inferiorly

The inferior mediastinum also
divided into
• Anterior
• Middle
• Posterior

Content of Superior Mediastinum
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Thymus gland
Great vessels
Arteries
Aorta and its branches.
Pulmonary trunk.
Veins
Superior Vena cava and its tributaries.
Trachea
Esophagus
Nerves
Phrenic: spinal nerve.
Vagus: cranial nerve.
Thoracic duct Moamer Gabsa

Thymus gland
• It is a primary lymphoid organ.
• Function: production of T-Lymphocytes.
• Is located in the inferior part of the neck and
the anterior part of the superior mediastinum.
• It lies posterior to the manubrium and extends
into the anterior mediastinum anterior to the
fibrous pericardium.
• Normal weight 5 – 50 gm
• After puberty the thymus undergoes gradual
involution and is largely replaced by fat
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Blood supply of thymus gland
Arterial supply: The anterior intercostal arteries.
Venous drainage into:
• The left brachiocephalic
• Internal thoracic.
• Inferior thyroid veins.
The lymphatics end in:
• The parasternal lymph nodes.
• Brachiocephalic lymph nodes.
• Tracheobronchial lymph nodes.
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Thymus gland
Great vessels
Arteries
Aorta and its branches.
Pulmonary trunk.
Veins
Superior Vena cava and its tributaries.
Trachea
Esophagus
Nerves
Phrenic: spinal nerve.
Vagus: cranial nerve.
Thoracic duct
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Aorta
• The aorta is the main arterial trunk
that delivers oxygenated blood from
the left ventricle of the heart to the
tissues of the body.
• It is divided for purposes of
description into the following parts :
• Ascending.
• Arch of the aorta.
• Descending (thoracic) .
• Abdominal aorta
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Ascending Aorta
• The ascending aorta begins at the base of the left
ventricle and runs upward and forward to come to lie
behind the right half of the sternum at the level of the
sternal angle where it becomes continuous with the arch
of the aorta.
• The ascending aorta lies within the fibrous pericardium
and is enclosed with the pulmonary trunk in a sheath of
serous pericardium.
• At its root it possesses three bulges, the sinuses of the
aorta, one behind each aortic valve cusp.
• Approximately 2.5 cm in diameter.
Branches
• The right coronary artery arises from the anterior aortic
sinus, and the left coronary artery arises from the left
posterior aortic sinus
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• The ascending aorta is intrapericardial
for this reason and because it lies inferior
to the transverse thoracic plane, it is
considered a content of the middle
mediastinum (part of the inferior
mediastinum).
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Arch of the Aorta
• The arch of the aorta is a continuation of
the ascending aorta.
• It lies behind the manubrium sterni and
arches upward backward and to the left
in front of the trachea (its main
direction is backward).
• It then passes downward to the left of the
trachea and at the level of the sternal
angle becomes continuous with the
descending aorta.
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Branches of arch of aorta
• The brachiocephalic artery arises from the convex
surface of the aortic arch. It passes upward and to the
right of the trachea and divides into the right
subclavian and right common carotid arteries behind
the right sternoclavicular joint
• The left common carotid artery arises from the
convex surface of the aortic arch on the left side of the
brachiocephalic artery. It runs upward and to the left of
the trachea and enters the neck behind the left
sternoclavicular joint.
• The left subclavian artery arises from the aortic arch
behind the left common carotid artery. It runs upward
along the left side of the trachea and the esophagus to
enter the root of the neck. It arches over the apex of the
left lung.
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Descending Thoracic Aorta
• It lies in the posterior mediastinum and begins as
a continuation of the arch of the aorta on the left
side of the lower border of the body of the fourth
thoracic vertebra.
• It runs downward in the posterior mediastinum,
inclining forward and medially to reach the
anterior surface of the vertebral column.
• At the level of the 12th thoracic vertebra it
passes behind the diaphragm (through the aortic
opening) in the midline and becomes continuous
with the abdominal aorta.
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Branches of descending aorta
• Posterior intercostal arteries are given off
to the lower nine intercostal spaces on each
side. Subcostal arteries are given off on each
side and run along the lower border of the
12th rib to enter the abdominal wall.
• Pericardial, esophageal and bronchial
arteries are small branches that are
distributed to these organs.
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Pulmonary Trunk
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• The pulmonary trunk conveys deoxygenated
blood from the right ventricle of the heart to the
lungs.
• It leaves the upper part of the right ventricle and
runs upward backward and to the left .
• It is about 2 in. (5 cm) long and terminates in the
concavity of the aortic arch by dividing into right
and left pulmonary arteries .
• Together with the ascending aorta, it is enclosed in
the fibrous pericardium and a sheath of serous
pericardium.

Branches of pulmonary trunk
• The right pulmonary artery runs to the right behind the
ascending aorta and superior vena cava to enter the root of the
right lung.
• The left pulmonary artery runs to the left in front of the
descending aorta to enter the root of the left lung.
• The ligamentum arteriosum is a fibrous band that connects
the bifurcation of the pulmonary trunk to the lower concave
surface of the aortic arch.
The ligamentum arteriosum is the remains of the ductus
arteriosus, which in the fetus conducts blood from the
pulmonary trunk to the aorta, thus bypassing the lungs.
The left recurrent laryngeal nerve hooks around the lower border
of this structure. After birth, the ductus closes. Should it
remain patent, aortic blood will enter the pulmonary circulation,
producing pulmonary hypertension and hypertrophy of the right
ventricle. Surgical ligation of the ductus is then necessary
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Superior Vena Cava
• Returns blood from all structures superior to the
diaphragm Except the lungs and heart.
• It passes inferiorly and ends at the level of the 3rd costal
cartilage where it enters the right atrium of the heart.
• The SVC lies in the right side of the superior
mediastinum, anterolateral to the trachea and
posterolateral to the ascending aorta.
• The right phrenic nerve lies between the SVC and the
mediastinal pleura.
• The terminal half of the SVC is in the middle
mediastinum, where it lies beside the ascending aorta
and forms the posterior boundary of the transverse
pericardial sinus.
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Tributaries
•Right brachiocephalic vein
•Left brachiocephalic vein
•Azygos vein
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Trachea
• The trachea is a mobile cartilaginous and
membranous tube.
• It begins in the neck as a continuation of the
larynx at the lower border of the cricoid
cartilage at the level of the sixth cervical
vertebra.
• It descends in the midline of the neck.
• In the thorax the trachea ends below at the carina
by dividing into right and left principal (main)
bronchi at the level of the sternal angle
(opposite the disc between the fourth and fifth
thoracic vertebrae).

• During expiration the bifurcation rises by
about one vertebral level and during deep
inspiration may be lowered as far as the sixth
thoracic vertebra.
• In adults the trachea is about 4½ in. (11.25 cm)
long and 1 in. (2.5 cm) in diameter.
• The fibroelastic tube is kept patent by the
presence of U-shaped bars (rings) of hyaline
cartilage embedded in its wall.
• The posterior free ends of the cartilage are
connected by smooth muscle the trachealis
muscle.

The relations of the trachea in the superior
mediastinum
• Anteriorly: The sternum, the thymus, the left
brachiocephalic vein, the origins of the brachiocephalic
and left common carotid arteries, and the arch of the
aorta.
• Posteriorly: The esophagus and the left recurrent
laryngeal nerve.
• Right side: The azygos vein, the right vagus nerve, and
the pleura.
• Left side: The arch of the aorta, the left common
carotid and left subclavian arteries, the left vagus and
left phrenic nerves, and the pleura.

Blood Supply of the Trachea
The upper two thirds are supplied by the inferior
thyroid arteries and the lower third is supplied by the
bronchial arteries.
Lymph Drainage of the Trachea
The lymph drains into the pretracheal and paratracheal
lymph nodes and the deep cervical nodes.
Nerve Supply of the Trachea
The sensory nerve supply is from the vagi and the
recurrent laryngeal nerves. Sympathetic nerves supply
the trachealis muscle.

Esophagus
•Muscular tube
(approximately 25 cm [10 in]
long) with an average
diameter of 2 cm that conveys
food from the pharynx to the
stomach

The esophagus normally has three
constrictions where adjacent structures
produce impressions:
• Cervical constriction (upper esophageal sphincter):
at its beginning at the pharyngoesophageal junction,
approximately 15 cm from the incisor teeth
• Thoracic (broncho-aortic) constriction: a compound
constriction where it is first crossed by the arch of the
aorta, 22.5 cm from the incisor teeth, and then where
it is crossed by the left main bronchus, 27.5 cm from
the incisor teeth
• Diaphragmatic constriction: where it passes through
the esophageal hiatus of the diaphragm,
approximately 40 cm from the incisor teeth

•The esophagogastric junction
lies to the left of the T11
vertebra on the horizontal
plane that passes through the
tip of the xiphoid process

The arterial supply of the
abdominal part of the esophagus is
from :
•The left gastric artery, a branch of
the celiac trunk.
•The left inferior phrenic artery

The venous drainage from:
• The submucosal veins of this part of the
esophagus is both to the portal venous
system through the left gastric vein
&
• into the systemic venous system through
esophageal veins entering the azygos vein.

The lymphatic drainage of the
abdominal part of the esophagus is into:
• the left gastric lymph nodes ,
efferent lymphatic vessels from
these nodes drain mainly to celiac
lymph nodes.

The esophagus is innervated by:
• The esophageal plexus, formed by the
vagal trunks (becoming anterior and
posterior gastric branches)
• The thoracic sympathetic trunks
via the greater (abdominopelvic)
splanchnic nerves and periarterial
plexuses around the left gastric and
inferior phrenic arteries.

Phrenic Nerve
• Spinal nerve.
• Roots are C3,4 and 5.
• Runs anterior to the roots of the lung.
• Supplies the diaphragm.
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Vagus Nerve
• Cranial nerve.
• Passes posterior to the roots of the
lung. It gives an important branches at
this area, Recurrent laryngeal nerves
(right and left).
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Recurrent laryngeal nerves
• The right recurrent laryngeal nerve:
Hooks around the right subclavian artery.
• The left recurrent laryngeal nerve:
Passes inferior to the arch of the aorta,
immediately lateral to the ligamentum
arteriosum.
Both nerves ascend to the larynx in the groove
between the trachea and the esophagus.
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Thoracic duct
• Largest lymphatic vessel.
• Starts at cisterna chyli.
• Ends at the junction of the left
subclavian and left internal jugular
veins.
Drain the lymph from:
• Lower limbs.
• Pelvis.
• Abdomen.
• Left upper limb.
• Left side of the thorax, head, and neck.
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Superior Mediastinum contents:
Muscles:
• Sternohyoid
• Sternothyroid
• Longus colli
Thymus: (in childhood &
puberty)
Veins:
• SVC
• Lt & Rt brachiocephalic
veins
• Lt Sup Intercostal vein
Arteries:
• Arch of Aorta
• Brachiocephalic artery
• Lt Common carotid
• Lt subclavian artery
Trachea & Esophagus
Nerves:
• Vagus
• Phrenic
Thoracic Duct
Lymph nodes:
• Brachiocephalic
• Tracheobronchial
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Inferior mediastinum
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• Superior mediastinum extend from
superior thoracic aperture (thoracic inlet)
superiorly to transverse thoracic plane
inferiorly
• The inferior mediastinum extend
from the transverse plane superiorly to
diaphragm inferiorly
Divisions of mediastinum

Anterior mediastinum
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Is bounded:
•Laterally by the pleurae
•Posteriorly by the pericardium
•Anteriorly by the sternum, the left
transverses thoracic and the fifth, sixth,
and seventh left costal cartilages.

Contents of anterior mediastinum
Moamer Gabsa
• 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
• Remnant of thymus
• Sternopericardial ligament

Middle Mediastinum
Contents:
Heart enclosed in pericardium
Arteries: Ascending Aorta,
Pulmonary trunk with its Left &
Right branches
Veins: SVC, Termination of
Azygos , Pulmonary veins
Nerves: Phrenic, Deep cardiac
plexus
Bifurcation of Trachea with
two principal bronchi
Tracheobronchial lymph nodes
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Posterior mediastinum
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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
•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
•Laterally by the mediastinal pleura

• Artery
• Thoracic part of the descending aorta
• Veins
• Azygos vein
• Hemiazygos vein
• Accessory hemiazygos vein
• Nerves
• Vagus nerve
• Splanchnic nerves
• Sympathetic chain
• Esophagus
• Thoracic duct
• Lymph glands Moamer Gabsa
Content of Posterior mediastinum

Azygos system
• Azygos vein.
• Hemiazygos.
• Accessory hemiazygos.
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• Alongside and Posterior to the thoracic duct, the veins that
drain the walls of the thorax the azygos and hemiazygos
veins.
• Each of these veins begin in the abdomen as the
ascending lumbar veins.
• The hemiazygos veins:
• The upper intercostal spaces are drained by the
superior hemiazygos vein and the lower the inferior
hemiazygos vein.
• These two veins may join as one hemiazygos vein that
passes behind the thoracic duct to empty into the
azygos vein.
• The two veins may just as frequently pass into the
azygos separately, forming two hemiazygos veins.
Moamer Gabsa
The azygos and hemiazygos veins

 If you reflect or remove the azygos system of veins,
the next structures in the posterior mediastinum
would be the splanchnic nerves
 Specifically the greater splanchnic nerves. These
nerves are derived from the sympathetic chains,
thoracic ganglion T5 to T10.
 The lesser splanchnic nerves that are derived from
ganglion T10 and T11.
 Some anatomist may describe the least splanchnic
that is derived from ganglion T12.
 Remember according to anatomists the sympathetic
chain is not part of the posterior mediastinum.
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Splanchnic nerves

The sympathetic chain
• Sympathetic ganglia are the ganglia of the
sympathetic nervous system. They deliver
information to the body about stress and
impending danger, and are responsible for
the familiar fight-or-flight response.
• They contain approximately 20,000–30,000
nerve cell bodies and are located close to
and on either side of the spinal cord in long
chains
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Moamer Gabsa
Level 1 Posterior pericardium
Level 2 The Esophagus & vagus Nerves
Level 3 The thoracic aorta
Level 4 The thoracic duct
Dissection of Posterior mediastinum
Level 5 The azygous system
Level 6 The Splanchnic nerves

References
• Harold Ellis, Clinical Anatomy, Applied anatomy for students and
junior doctors, 11th Ed, Blackwell Publishing Ltd, 2006
• Richard Snell, Clinical Anatomy by Regions, 8th Ed. Lippincott
Williams & Wilkins.
• Moore, Keith L.; Dalley, Arthur F, Clinically Oriented Anatomy, 5th
Ed. Lippincott Williams & Wilkins; 2006.
• Agur, Anne M.R.; Dalley, Arthur F. Grant’s Atlas of Human
Anatomy. 12th Ed. Lippincott Williams & Wilkins; 2009.
• Elaine N. Marieb, R.N.; Patricia Brady Wilhelm ; Jon Mallatt. Human
anatomy. 6th edition, Pearson Education, Inc. ; 2012
Moamer Gabsa

Superior and inferior mediastinum

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