Superior Mediastinum

Question 1

What is the mediastinum

Answer 1

The mediastinum is the central compartment of the thoracic cavity, located between the two pleural sacs. It contains most of the thoracic organs, and acts as a conduit for structures traversing the thorax on their way into the abdomen.

Question 2

How is the mediastinum anatomically divided

Answer 2

Anatomically, the mediastinum is divided into two parts by an imaginary line that runs from the sternal angle (the angle formed by the junction of the sternal body and manubrium) to the T4 vertebrae:

Question 3

Superior mediastinum

Answer 3

extends upwards, terminating at the superior thoracic aperture.

Question 4

Inferior mediastinum

Answer 4

extends downwards, terminating at the diaphragm. It is further subdivided into the anterior mediastinum, middle mediastinum and posterior mediastinum.

Question 5

The superior mediastinum is bordered by the following thoracic structures:

Answer 5

Superior – Thoracic inlet.
Inferior – Continuous with the inferior mediastinum at the level of the sternal angle.
Anterior – Manubrium of the sternum.
Posterior – Vertebral bodies of T1-4.
Lateral – Pleurae of the lungs.

Question 6

The superior mediastinum contains

Answer 6

neural, vascular and respiratory structures passing from the adjacent regions of the neck and abdomen (via the inferior mediastinum).

Question 7

Left Common carotid artery

Answer 7

to the left side of the head & neck.

Question 8

Brachiocephalic artery

Answer 8

supplying the right side of the head & neck and the right upper limb.

Question 9

The following tributaries of the superior vena cava are located within the superior mediastinum:

Answer 9

Brachiocephalic veins
Left superior intercostal vein
Supreme intercostal vein
Azygos vein

Question 10

Supreme intercostal vein –

Answer 10

drains the vein from first intercostal space directly into the brachiocephalic veins.

Question 11

Left superior intercostal vein –

Answer 11

collects blood from the left 2nd and 3rd intercostal vein. It drains into the left brachiocephalic vein.

Question 12

Brachiocephalic veins

Answer 12

– draining blood from the upper body.

Question 13

In the superior mediastinum, the vagus nerve has two distinctive paths:

Answer 13

• Right vagus nerve

- Left vagus nerve

Question 14

In the superior mediastinum, the vagus nerve has two distinctive paths:

Answer 14

• Right vagus nerve

- Left vagus nerve

Question 15

Right vagus nerve –

Answer 15

runs parallel to the trachea and passes posteriorly to the superior vena cava and the right primary bronchus.

Question 16

Left vagus nerve

Answer 16

enters the superior mediastinum between the left common carotid and the left subclavian arteries. It descends anteriorly to the aortic arch, before travelling posterior to the left bronchus.

Question 17

Origin and route of the phrenic nerve

Answer 17

From the anterior surface of the anterior scalene muscle, the phrenic nerves (roots C3, C4 and C5) enter the superior mediastinum lateral to the great vessels. They then descend anteriorly into the middle mediastinum, passing anteriorly to the hilum of the lungs.

Question 18

where do Cardiac nerves originate

Answer 18

Cardiac nerves – originate from the superior, middle and inferior cardiac ganglion and form the superficial and deep cardiac plexuses in the superior mediastinum.

Question 19

The superior plexus sits

Answer 19

between the aortic arch and right pulmonary vein

Question 20

The deep plexus lies

Answer 20

on the surface of the trachea at the point of bifurcation.

Question 21

Sympathetic trunk runs

Answer 21

bilaterally to the vertebral bodies along the entire length of the vertebral column.

Question 22

most anterior structure within the superior mediastinum

Answer 22

The thymus gland - It sits flush against the posterior surface of the sternum and extends into the anterior mediastinum and can often reach into the neck.

Question 23

Route of The trachea

Answer 23

The trachea bifurcates into the primary bronchi posterior to the ascending aorta at the level of the sternal angle.

Question 24

Route of The oesophagus

Answer 24

The oesophagus ascends towards the pharynx, which it joins at the level of C6.

Question 25

Route of the thoracic duct

Answer 25

In the superior mediastinum, the thoracic duct passes to the left of the oesophagus on its path to the junction of the left internal jugular and subclavian veins.

Question 26

Muscles in the superior mediastinum

Answer 26

The sternohyoid and sternothyroid muscles

Question 27

Route of The sternohyoid and sternothyroid muscles

Answer 27

The sternohyoid and sternothyroid muscles originate from the posterior surface of the manubrium. They are part of the infrahyoid muscle group of the neck.

The inferior aspect of the longus colli muscle also originates within the superior mediastinum.