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THORAX – FROM 128PG MOORES
OVERVIEW OF MEDIASTINUM
Meaning of mediastinum: it is the division of the thoracic cavity
Positions:
1
...
Anterior to posterior : sternum and costal cartilages to bodies of the
thoracic vertebrae
• Also called the middle septum
• It is the central compartment of the thoracic cavity
• It is covered by the mediastinal pleura on each side
• It consists of thoracic viscera (thyroid gland, trachea, and
esophagus) and heart, except lungs which are hollow and air or
liquid filled structures
...

Sternopericardial ligaments: helps to attach the fibrous pericardium to
the posterior surface of the sternum
It is bound to the structure of the posterior mediastinum by the loose
connective tissue
It protects the heart against sudden overfilling since it is doesn’t give way to pressure (unyielding) and is close to
the great vessels that pierce it superiorly

Serous pericardium:
• It is composed of mesothelial cells (single layer of flattened cells)
• It is also known as the ‘collapsed sac’
i
...
Visceral layer of serous pericardium: inner layer, lines the outer layer of the heart and also called the
epicardium
• It forms the epicardium which is the outermost of the 3 layers of heart wall
• Starts from the great vessels→goes along parietal layer of serous pericardium
• Here it meets →aorta and the pulmonary trunk leaving the heart
→Superior vena cava, inferior vena cava and pulmonary veins enter the heart

Pericardiacophrenic ligament:
It is the continuity of the fibrous pericardium with the central tendon of the diaphragm
▪ The two aren’t separable by dissection
▪ Hence it keeps the heart tethered in place inside the fibrous sac

Coverage of the pericardium on the heart;
▪ The heart and the pericardial sac is situated obliquely →2/3rd on the left and 1/3rd on the right medially
How to figure this out?
• Moving your face 45 degrees to the left, that’s how the heart is positioned relative to the trunk

Pericardial cavity:
It is a potential space between the parietal and visceral layers of serous pericardium
It contains a thin film of fluid that helps the heart move and beat frictionless

Pericardial sinus:
•
•

They are impressions in the pericardial sac formed
between the points where great vessels enter it
...

Function:
 During cardiac surgery, the transverse pericardial sinus allows a surgeon to isolate the pulmonary trunk and
ascending aorta and apply a temporary ligature or clamp
Oblique pericardial sinus:
Located according the picture
• It is a wide pocket-like recess in the pericardial cavity posterior to the base of the heart, formed by the left
atrium
• Bounded laterally by : pericardial reflections surrounding the pulmonary veins and IVC and posteriorly by the
pericardium overlying the anterior aspect of the esophagus
• It is a blind sac, hence cant penetrate fingers to reach the above structures
Function:
 Provides expansion space for the left atrium
...
Pericardiacophrenic artery (main) : branch of internal thoracic
artery
Smaller branches:
2
...
Bronchial, esophageal and superior phrenic arteries branches
of the thoracic aorta
4
...
Thymus
2
...
Inferior continuation of cervical viscera :
• Trachea anteriorly and esophagus posteriorly
• Nerves: left recurrent laryngeal nerve
4
...
Why? → cause it passes from the left to the right side,
anterior to the roots if the 3 major braches of arch of the aorta
These veins shunt blood from the head, neck and upper limbs to the right atrium

Superior vena cava (SVC):
❖ Returns blood from all the structures superior to the diaphragm, except the lungs and heart
❖ Passes inferiorly and ends at the level of 3rd costal cartilage, where it enters the right atrium of the heart
❖ It lies at the right side of the superior mediastinum, anteriorlateral to the trachea and posterolateral to the
ascending aorta
❖ Right phrenic nerve lies between the SVC and mediastinal pleura
❖ Terminal half of it lies in the middle mediastinum
❖ It forms the posterior boundary of the transverse pericardial sinus
Ascending aorta:
 It is 2
...
Why? → Cause it lies inferior to the thoracic plane and is content of the middle
mediastinum (part of inferior mediastinum)
Arch of aorta:
o It is curved and beings posterior to the 2nd right sternocostal (SC) joint at the level of sternal angle
o It arches superiorly, posteriorly and to the left and then inferiorly: ascends anterior to the right pulmonary and
artery bifurcation of trachea→ reaches apex at the left side of trachea and esophagus→ passes over root of left
lung→ descends posterior to the left root of the lung beside the T4 vertebra
o Termination : by becoming the thoracic (descending) aorta posterior to the 2nd left sternocostal joint
Arch of the azygos vein:
➢ Located right side of the trachea along the aorta over the root of the right lung
➢ But the blood flows in the opposite direction
➢ Branches of the arch: brachiocephalic trunk, left common carotid artery and left subclavian artery
Ligamentum arteriosum:
 It is the remnant of the fetal ductus arteriosus
 It passes from the root of the left pulmonary artery to the inferior surface of the arch of the aorta
Brachiocephalic trunk:
▪ The first and largest branch of the arch of the aorta
▪ Arises posterior to the manubrium, here it is anterior tot the trachea and posterior to the left brachiocephalic
vein
▪ The trunk then divides into right common carotid artery and right subclavian arteries
...
Right vagus nerve(RVN):
 Enters thorax anterior to the right subclavian artery
 Gives rise to the nerve below
2
...
Left vagus nerve:
 Descends in the neck posterior to the left common carotid artery
 It enters the mediastinum between the left common carotid artery and left subclavian artery
 It is separated by the phrenic nerve by the left superior intercostals vein
 It passes posterior to the root of the left lung and breaks into branches that contribute to left pulmonary
plexus
 It then leaves this and forms the esophageal nerve plexus by joining the right vagus
 When it curves medially at the inferior border of the arch of the aorta, it gives off the nerve below
4
...
Right phrenic nerve:
 Passes
6
...
These are not included
because they lie laterally to the vertebral bodies and are not within the posterior mediastinal compartment or space
...
)
Continued:
Location: The thoracic aorta lies posterior to the root of the
left lung, pericardium and esophagus
Termination: anterior to the inferior border of the T12
vertebra and enters abdomen through the aortic hiatus in
the diaphragm
Ascending aorta: branches are right and left coronary
arteries
Arch of the aorta: branches are brachiocephalic, left common
carotid, left subclavian

Branches of the descending aorta:
It has 3 vascular planes where is roams in:
→ Anterior, midline plane of unpaired visceral branches : to the gut (A)
→ Lateral planes of paried visceral branches : serves viscera other than
the gut and its derivatives (B)
→ Posterolateral planes of paired (segmental) parietal branches : to
the bodywall (C)
The branches of the descending thorax are:
1
...
Mediastinal arteries
3
...
Pericardial arteries
5
...
The arch of aorta : most evident in a postero-anterior radiograph (after a barium swallow)
2
...
The diaphragm
No compressions are visible in the empty esophagus

Thoracic duct and lymphatic trunk:
Thoracic duct:
• Largest lymphatic channel in the body
• Location: anterior aspect of the bodies of inferior 7 thoracic vertebrae
• It conveys most lymph of the body to the venous system, from: pelvic cavity, abdominal cavity, left upper limb,
left side of the thorax, head and neck, all that except from the right superior quadrant
• It originates from the cisterna chyli (chyle cistern) in the abdomen and ascends through the aortic hiatus in the
diaphragm
• The duct is thin walled and dull white, beaded because of its numerous valves
• It then ascends : in the posterior mediastinum among the thoracic aorta on its left, the azygos vein on ites right,
the esophagus anteriorly and the vertebral bodies posteriorly
• Ascends in the superior mediastinum: at the level of T4, T5, T6 vertebra, the thoracic duct crosses to the left,
posterior to the esophagus
• Branches: receives branches from the middle and superior intercostals spaces of both the sides through several
collecting trunks, posterior mediastinal structures
• Termination: it receives the jugular, subclavian, and bronchomediastinal lymphatic trunks
 Hence it empties into the venous system near the union of the left internal jugular and subclavian veins
→ the left venous angle or origin of the left brachiocephalic vein

VESSELS AND LYMPH NODES OF POSTERIOR MEDIASTINUM
Lymph nodes:
❖ Lies posterior to the pericardium, near the thoracic aorta and esophagus
❖ More are present posterior, anterior and lateral to esophagus (upto 8)
❖ They receive lymph from: esophagus, posterior aspect of pericardium, diaphragm, middle posterior intecostal
spaces
❖ Drainage to : right and left venous angles via right lymphatic duct or thoracic duct
Azygous system of veins:
o Present on each side of vertebral column
o Drainage : the back, thoracoabdominal walls, mediastinal viscera
o Branches: azygos vein (unpaired) and its main tributary the hemiazygos vein
o They both arise from the roots of the posterior aspect of the inferior vena cava (IVC) &/or renal veins
respectively
o They then merge with the ascending lumbar veins

Azygos vein:
▪ Pathway: between superior and inferior vena cava
▪ Drainage: blood from the posterior wall of the thorax and abdomen
▪ It passes along the right sides of the bodies of the inferior 8 thoracic vertebrae
▪ Arches over the superior aspect of the root of the right lung to join the SVC (just like the aorta arch pass over the
root of left lung)
▪ Along with the posterior intercostals veins these communicates with the vertebral venous plexus that drains the
: back, vertebra and the structures in the vertebral canal
▪ This vein also receives : mediastinal, esophageal and bronchial veins
Hemi-azygos vein:
o Arises: on the left side by the junction of the left sub costal and ascending lumbar veins
o Pathway: ascends on the left side of the vertebral column, posterior to thoracic aorta as far as T9 vertebra
o It then crosses right and posterior to the aorta, thoracic duct and esophagus and joins azygos vein
o It receives the inferior 3 posterior intercostals veins, the inferior esophageal veins and several small mediastinal
veins
Accessory hemi-azygos veins:
• Begins at the 4th or 5th intercostals space and descends on the left side of the vertebral column from T5 through
T8
• Receives tributaries from veins in 4th and 8th intercostals spaces and some from left bronchial veins
• Then it crosses the T7 or T8 vertebra, posterior to the thoracic aorta and thoracic duct joining the azygos vein
• Sometimes this vein joins the hemiazygos and opens with it into azygos vein
• This vein is frequently connected to the left superior intercostal vein (this vein drains the 1st to 3rd intercostals
spaces) for which it drains into the left brachiocephalic vein

Nerves of posterior mediastinum
There are 2 nerves:
1
...
Lower thoracic splanchnic nerves:
o Also known as greater, lesser and least splanchnic nerves
o They are a part of abdominopelvic splanchnic nerves
...

o They supply sympathetic innervations to the abdominal viscera

Anterior mediastinum:
It is the smallest division of all mediastinum
It lies between the sternum and the transverse thoracis muscles anteriorly and pericardium posteriorly
It lies between the sternum (sup) and diaphragm (inf)
It consists of:
o Loose connective tissue→sternopericardial ligaments
o Fat, lymphatic vessels, nodes
o Branches of internal thoracic vessels

In children and infants, it consist of the inferior part of the thymus
 Unusual case: it may extend to the 4th costal cartilage

Surface anatomy of the heart and the mediastinal viscera
Borders of the heart depend on:
1
...
Build and condition of the person
It can be variable
 The superior border corresponds to a line connecting the inferior border of the 2nd left costal cartilage to the
superior border of the 3rd right costal cartilage
...

 The inferior border corresponds to a line drawn from the inferior end of the right border to a point in the 5th
intercostal space close to the left MCL; the left end of this line corresponds to the location of the apex of the heart
and the apex beat
 The left border corresponds to a line connecting the left ends of the lines representing the superior and inferior
borders
...
Pulmonary area
2
...
Mitral area
4

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