The Mediastinum

Question 1

What 4 structures does the mediastinum extend to?

Answer 1

Thoracic inlet/aperture
Diaphragm
Sternum and costal cartilages
Thoracic vertebrae

Question 2

What features of the mediastinum make it highly mobile in living people?

Answer 2

Contains hollow, air or fluid-filled structures

Allows for movement of the lungs, heart, great vessels and oesophagus

Question 3

What splits the mediastinum into its superior and inferior parts? What vertebral level is this at?

Answer 3

Transthoracic plane (manubriosternal joint/sternal angle)
T4/5

Question 4

What is the position of the aortic arch, tracheal bifurcation and central tendon when a person is in the supine position?

Answer 4

Aortic arch lies superior to transthoracic plane
Tracheal bifurcation transected to transthoracic plane
Central tendon lies at level of xiphisternal junction and T9

Question 5

What is the position of the aortic arch, tracheal bifurcation and central tendon when a person is standing?

Answer 5

Arch of aorta transected by transverse thoracic plane
Tracheal bifurcation lies inferior to transthoracic plane
Central tendon may fall to middle of xiphoid process T9-10 IV disc

Question 6

What is contained in the superior mediastinum?

Answer 6

Brachiocephalic veins and superior vena cava
Great vessels
Ascending and arch of aorta
Trachea
Oesophagus
Thymus gland

Question 7

What is contained in the inferior mediastinum?

Answer 7

Heart
Oesophagus
Descending aorta
Inferior vena cava

Question 8

Which nerves run through the superior mediastinum?

Answer 8

Phrenic nerve (C3, 4 ,5 - innervation to diaphragm)
Vagus nerve and recurrent laryngeal nerves

Question 9

Which vessels/ducts are located in the superior mediastinum?

Answer 9

Brachiocephalic vein and superior vena cava
Arch of aorta and great vessels
Thoracic ducts and lymphatic trunks

Question 10

What cranial nerve is the vagus nerve and what does it provide innervation to?

Answer 10

CN X - cranial nerve 10
Innervation to oesophagus, heart and bronchi
Recurrent laryngeal loops back to innervate larynx (right – under right subclavian artery,
left – under arch of aorta)

Question 11

What vertebral level is the phrenic nerve at and what does it innervate?

Answer 11

C3-5
Motor to diaphragm
Sensory to pericardium, mediastinal pleura

Question 12

Why and how often does phrenic nerve paralysis occur? What does it cause and how is it confirmed?

Answer 12

Rare (approx 8%) complication following chest surgery - mostly transient
Results in elevation of ipsilateral hemidiaphragm
Post-operative radiograph confirms

Question 13

What vertebral level is the trachea at? What are some of its features?

Answer 13

C6-T4
Cartilaginous rings U shaped
Carina (bifurcation into primary bronchi) at transthoracic plane T4/5
Aorta arches over left main bronchus and lung root

Question 14

What vertebral level is the oesophagus at? What are some of its features?

Answer 14

C6-10
Immediately posterior to trachea
Inclines to the left but compressed by the aortic arch (T4) and the root of the left lung (left main bronchus T5-T6)

Question 15

What is the contents of the inferior mediastinum?

Answer 15

Anterior mediastinum
o	Thymus
Middle mediastinum
o	Pericardium and heart
Posterior mediastinum
o	Primary bronchi
o	Oesophagus (& oesophageal plexus)
o	Descending aorta
o	Thoracic duct
o	Azygos and hemi azygos veins

Question 16

What are the features of the pericardium?

Answer 16

Tough outer fibrous pericardium stabilizes the heart
o Prevents over-dilation
Serous pericardium (the collapsed sac)
o Parietal pericardium
o Visceral pericardium
As heart grows into the serous sac is fills pericardial cavity
o Leaves potential space between layers of serous pericardium

Question 17

What is the arterial supply to the posterior thoracic wall?

Answer 17

Posterior intercostal arteries are branches of descending aorta
Except 1 and 2, which branch from costocervical trunk which comes off the subclavian arteries

Question 18

Where are the anterior intercostal arteries supplied from?

Answer 18

From internal thoracic artery which runs deep to costal cartilages
Internal thoracic artery from subclavian arteries

Question 19

Where are the anterior intercostal arteries located?

Answer 19

Run in upper part of each intercostal space (with their corresponding nerve and vein in neurovascular bundle) in then costal groove
Smaller collateral branch in inferior part of the intercostal space

Question 20

What do the anterior intercostal arteries anastomose with in each space?

Answer 20

Posterior intercostal arteries

Question 21

What is the azygos system and what does it contain?

Answer 21

Thoracic venous drainage
Veins more variations
Anterior intercostal veins
o	Internal thoracic vein
Posterior intercostal veins
o	Azygos vein – right
o	Hemiazygos veins – left