UNIT 4: The mediastinum

Question 1

What are the main divisions and the landmarks of these divisions in the mediastinum?

Answer 1

Superior and inferior, division made at the sternal angle at level T4.
Superior extends to the thoracic inlet and the inferior descends to the diaphragm.
The inferior then splits into the anterior, middle and posterior, boundaries set by the pericardial sac.

Question 2

What are the boundaries of the superior mediastinum?

Answer 2

Superior - thoracic inlet
Lateral - pleural cavity
Inferior - inferior mediastinum at T4
Anterior - the manubrium of the sternum.
Posterior - vertebral level T1 to T4.

Question 3

What vasculature is found in the superior mediastinum?

Answer 3

Arch of the aorta and its branches (ABCS), brachiocephalis, left common carotid, left subclavian.
tributaries of the superior vena cave:
- brachiocephalic vein (L+R): upper body
- azygous vein: hemizygous veins drain the right posterior intercostal veins.
-supreme intercostal vein: 1st intercostal into brachio
- superior intercostal vein: 2nd and 3rd intercostal space into Brachio

Question 4

What innervation is found in the superior mediastinum?

Answer 4

Vagus nerve
Phrenic nerve
Cardiac nerves
Sympathetic trunk

Question 5

What are the divisions of the vagus nerve and where are they found?

Answer 5

Right vagus nerve - parralel to the trachea, posteroir to the SVC and PT.
Left vagus nerve - enters between the left common carotid and the left subclavian, travels anteriorly to the aortic arch, then posteriorly to the bronchus.
The left vagus nerve divides into the left recurrent laryngeal nerve as it passes through the aortic arch, travels to the left of the ligamentun arteriosum, then in the tracheal oesophageal groove.

Question 6

What is the route of the phrenic nerves?

Answer 6

Roots C3,C4,C5, from the anterior surface of the anterior scalene muscles.
Descend anteriorly into the middle mediastinum and pass the hilum of the lungs anteriorly.

Question 7

What is the route of the cardiac nerves?

Answer 7

Orignate from the superior, inferior and middle cardiac ganglion, form the superficial and deep cardiac plexus.
The superficial plexus sits between the aortic arch and the right pulmonary artery.
The deep plexus sits where the trachea bifurcates.

Question 8

Where is the sympathetic trunk found?

Answer 8

Runs bilaterally along the full length of the vertebral column.

Question 9

Explain the location of the thymus.

Answer 9

Is the most anterior part of the superior mediastinum, often descends into the anterior (inferior) mediastinum and upwards into the neck.
Is just deep to the surface of the menubrium.

Question 10

Where is the trachea in relation to the ascending aorta?

Answer 10

Posterior to the ascedning aorta

Question 11

At what level is the boundary between the oesophagus and the pharynx?

Answer 11

C6

Question 12

What muscles can be found in the superior mediastinum?

Answer 12

The sternohyoid and the sternothyroid (infrahyoid muscles)
Inferior aspect of the longus colli muscle.

Question 13

What are the boundaries of the anterior mediastinum?

Answer 13

Anterior : sternal body and the transverse thoracic muscle.
Posterior: pericardial sac
Lateral: Mediastinal pleura
Superior: Superior mediastinum
Inferior : Diaphragm

Question 14

What is found in the anterior mediastinum?

Answer 14

Mostly loose connective tissue (Sternopericardial ligaments)
Adipose tissue
Branches of vessels in the mediastinum
Thymus in infants and young children

Question 15

How does the location of the thymus change with age?

Answer 15

As a person ages, the thymus recedes (mostly during puberty) so the thymus no longer sits in the anterior mediastinum, only the superior.

Question 16

What are the borders of the middle mediastinum?

Answer 16

The borders of the pericardium.

Question 17

What organs are found within the middle mediastinum?

Answer 17

The heart, the pericardium, the trachea bifurcation into the bronchi

Question 18

What vasculature passess through the middle mediastinum?

Answer 18

The ascending aorta - and the left and right coronary arteries
The pulmonary trunk
The superior vena cava

Question 19

What are the two main vessels that drain into the superior vena cava?

Answer 19

The left and right brachiocephalic veins.

Question 20

What innervation if found in the middle mediastinum?

Answer 20

The phrenic nerves
The cardiac plexus

Question 21

What type of innervation do the phrenic nerves supply to the diaphragm?

Answer 21

Motor innvervation

Question 22

What is the origin of fibres found in the cardiac plexus?

Answer 22

Sympathetic: T1 to T4 of the spinal cord
Parasympathetic: Vagus nerve

Question 23

What lymphatics are found in the middle mediastinum?

Answer 23

The tracheobranchial lymph nodes, made from the joining of bronchial lymph nodes at the hilum of the lung.

Question 24

What are the borders of the posterior mediastinum?

Answer 24

Posterior - T5 to T12
Anterior - middle mediastinum
Lateral - mediastinal pleura
Superior - superior mediastinum
Inferior - diaphragm.

Question 25

What is the journey of the thoracic aorta in the posterior mediastinum?

Answer 25

Arises at T4.
Travels to the left of the vertebrae and becomes more medial as it descends.
Becomes the abdominal aorta as it passes through the hiatus in the diaphragm at T12.
Branches into the posterior intercostal arteries, the bronchial arteries, oesophageal arteries and the superior phrenic arteries.

Question 26

What are the oesophageal plexus origins and follow ons?

Answer 26

Originates from the combining of the vagus nerves.
Just above the diaphragm it converges to form the anterior and posterior vagal trunk.

Question 27

What makes up the azygous system of veins?

Answer 27

Azygous vein - formed by the combination of the right lumbar and the right subcostal vein, enter the mediastinum from the aortic hiatus
Hemiazygous vein - combination of left lumbar and left subcostal vein, passes through the left curs of the diaphragm, combines with the azygous vein at T8.
Accessory hemiazygous vein - Union of the fourth to eight intercostal vein, drains into azygous at T7.