Superior Mediastinum

Question 1

Where does the superior mediastinum sit

Answer 1

Posterior to the manubrium of the sternum

Anterior to the first four thoracic vertebrae.

Question 2

What is meant by the mediastinum

Answer 2

Is a thick midline partition that separates the two pleural cavities.
It extends from the superior thoracic aperture (inlet) to the inferior thoracic aperture and between the sternum anteriorly and the thoracic vertebrae posteriorly

It acts as a conduit for structures that pass through the thorax from one body region to another and for structures that connect thoracic organs to other body regions

Question 3

List the contents of the mediastinum

Answer 3

trachea - from larynx to bifurcation into principal (right and left main) bronchi
oesophagus- from pharynx - muscular tube – pierces diaphragm at level of T10
heart and pericardium
thoracic duct - lymphatic drainage
nerves
great vessels

Question 4

Describe the differences in the size of the heart using AP and PA X-rays

Answer 4

AP and PA X-rays are different views of the dimensions of the chest
If the structure is at the front of the chest, and the X-ray is at the back, X-rays will spread out before reaching the structure and X-rays close to the structure (not much difference in dispersion).
Results in different sizes
Hence heart appears larger on an AP X-ray

Question 5

Why is the second rib not at T2 level

Answer 5

Ribs slope downwards- and so rib 2 articulates with T4/5.

Question 6

What is the difference between the pharynx and larynx

Answer 6

Pharynx- G.I tract in throat

Larynx- airway in throat.

Question 7

Ay which vertebral levels do structures pass through the diaphragm

Answer 7

T8- IVC
T10- Oesophagus
T12- Descending aorta

Question 8

Describe the relevance of different vertebral levels in the thorax

Answer 8

T8,10,12- extent of pleural cavity

T6,8,10- extent of lungs

Question 9

Describe the divisions of the mediastinum

Answer 9

Superior: above sternal angle
Inferior: below sternal angle to the inferior thoracic aperture (further divided):
Anterior: anterior to heart in pericardial sac
Middle: pericardial sac & heart
Posterior: posterior to pericardial sac and diaphragm

Question 10

List the contents of the superior mediastinum

Answer 10

From anterior to posterior:
Thymus
Phrenic Nerves
Great veins
Main lymphatic trunks
Vagus nerves
Great arteries
Trachea and main bronchi
Upper oesophagus

Question 11

Describe the boundaries of the mediastinum

Answer 11

Superior boundary- oblique plane passing from the jugular notch upward and posteriorly to the superior border of T1
Inferiorly- Transverse plane passing from the sternal angle to the intervertebral disc between T4/5
Laterally- mediastinal part of the parietal pleura.

Question 12

Describe the great veins found in the superior mediastinum

Answer 12

The SVC is vertically orientated and begins posterior to the lower edge of the right first costal cartilage and terminates at the lower right third costal cartilage where it joins the right atrium.#
The lower half of the SVC is within the pericardial sac and therefore is contained in the middle mediastinum.

Inferior Vena Cava (IVC) enters right atrium from below, through central tendon of diaphragm- the heart sits on the central tendon.
Most of the IVC is present in the abdomen, once it passes through the central tendon it is in the right atrium.

Question 13

Describe the formation of the SVC

Answer 13

formed by asymmetric union of right and left brachiocephalic veins, of which each forms an internal jugular (from head) and subclavian vein (from upper limbs); left brachiocephalic crosses posterior to the manubrium to join the right and form the SVC.
The union is on the right- not the centre.
Left subclavian- follows oblique course of sternoclavicular joint.

Question 14

Where do the veins sit in relation to the arteries

Answer 14

More anteriorly

Question 15

Describe the venous drainage of the anterior chest wall

Answer 15

Anterior intercostal veins drain into the internal thoracic vein which connect with the brachiocephalic veins in the neck.

Question 16

Describe the venous drainage of the posterior chest wall

Answer 16

Drains the posterior wall of the thorax and abdomen
Arches over the right lung root
Drains into the SVC
has many branches (posterior intercostal veins) at the posterior of the chest next to vertebrae [asymmetric, with most on right side of the body - only accessory hemiazygous veins (above) and hemiazygous vein (below) on left)
Upper posterior regions may drain into left and right supreme intercostal veins.
left empties into left brachiocephalic
right empties into azygos.

Question 17

What are the arteries of the superior mediastinum

Answer 17

Ascending aorta

Arch of aorta

Descending aorta

Question 18

What are the branches of the ascending aorta

Answer 18

left/right coronary arteries branch from superior of the aortic valve to ensure heart gets best blood supply

Question 19

Where do the left hemiazygos and accessory veins drain

Answer 19

Into the right atrium

Question 20

Describe the branches of the aortic arch

Answer 20

Brachiocephalic trunk – divides into right common carotid and right subclavian arteries
Left common carotid artery
Left subclavian artery

Question 21

Describe the course of the ascending aorta

Answer 21

Only the arch of the aorta is in the superior mediastinum.
It begins when the ascending aorta emerges from the pericardial sac and courses upward, backward and to the left as it passes through the superior mediastinum, ending at the vertebral level T4/5,
It can extend as high as the midline of the manubrium and sternum.
The arch is initially anterior and finally lateral to the trachea.

Question 22

Describe the relations of the aorta and great arteries to the airway

Answer 22

Aortic arch arises anterior to trachea
Arches over the left main bronchus at the lung root
Trachea lies behind & between brachiocephalic and left common carotid arteries
trachea lies behind and between brachiocephalic and left common carotid arteries

Question 23

Describe the common carotids

Answer 23

divide to external and internal carotids high in neck, supplying the head and neck alongside the vertebral arteries from the subclavian arteries

Question 24

Describe the descending aorta

Answer 24

Aorta higher at front than back
descending aorta (after the arch, running down back of chest to abdomen (exiting at T12))

Question 25

Describe the pulmonary trunk

Answer 25

outflow of right ventricle, travelling backwards to get behind aortic arch and carrying deoxygenated blood to lungs via left/right pulmonary arteries

Question 26

Describe the ligamentum arteriosum

Answer 26

Connects the pulmonary trunk with the arch of the aorta and allows blood to bypass the lungs during development of the foetus.
Closes soon after birth and forms the ligamentous connection seen in the adult.
Ligamentum arteriosum connects PT to aortic arch. Is remnant of the ductus arteriosus – bypasses lungs in foetal life.

Question 27

Describe the phrenic nerves

Answer 27

Formed in the cervical plexus from C3, 4, 5
Motor to the diaphragm
Sensory to:
central tendon of the diaphragm
mediastinal pleura
pericardium (fibrous and parietal layer of serous pericardium)
peritoneum of central diaphragm