Part 4: Superior Mediastinum

Question 1

Describe the general asymmetry of the superior mediastinum

Answer 1

Veins are on right and arteries on left

Question 2

What are the boundaries of the superior mediastinum

Answer 2

Anterior: Manubrium
Posterior: T1-4

Question 3

Which structures occupy the midline of thoracic inlet?

Answer 3

Trachea and oesphagus

Question 4

Describe the aortic arch

Answer 4

Arises from LV. Arch passes from front to back with concavity at level of 2nd CCJ over L bronchus and pulmonary trunk bifurcation. At apex gives off brachiocephalic trunk, then L common carotid and L subclavian just behind L SC joint.

Question 5

Where does ligamentum arteriosum join?

Answer 5

Remains of ductus arteriosus. Attaches from L pulmonary trunk to aortic arch just after L SC artery.

Question 6

What physiologic receptors are in the aortic arch?

Answer 6

Baroreceptors - in adventitial layer, contribute to heart rate
Aortic bodies - like carotid bodies help detect hypoxia important with respiratory reflexes

Question 7

Describe the formation of the SVC

Answer 7

Brachiocephalic veins arm formed just behind SC joints bilaterally from IJV and SCV. The IJV lies lateral to CCA in front of scalenus anterior. R BCV runs downward while L BCV runs almost horizontal. The 2 merge to form SVC at 1st R costal cartilage

Question 8

What veins other than brachiocephalic drain into SVC?

Answer 8

vertebral, internal thoracic, inferior thyroid plexus, left superior intercostal and large thymic join at commencement.
Azygous joins at 2nd costal cartilage.

Question 9

Describe course of SVC

Answer 9

Begins at 1st costal cartilage - border of sternum
Pierced by azygous vein 2nd costal cartilage
Enters upper border of RA at 3rd costal cartilage

Question 10

Where does the thoracic duct empty?

Answer 10

At commencement of SVC

Question 11

The cardiac plexus consists of deep and superficial parts. What contributes to superficial part?

Answer 11

Union of L vagus and L cervical sympathetic ganglion

Question 12

What forms deep part of cardiac plexus?

Answer 12

Fibres from L+R vagus, recurrent laryngeal, cervical and sympathetic ganglion

Question 13

Where does the trachea commence superiorly?

Answer 13

C6 - continuation of larynx

Question 14

What are the anterior and posterior relationships of the trachea?

Answer 14

Anterior: Manubrium with sternohyoid and sternothyroid on each side. Brachiocephalic trunk and L CCA diverge each side
Posteriorly: Oesphagus

Question 15

What are the left and right relationships of the trachea?

Answer 15

Right: Right brachiocephalic and SVC, vagus nerve and arch of azygous
Left: L CCA, L SCV, aortic arch, left recurrent laryngeal nerve

Question 16

Where does the pulmonary trunk lie in relation to the trachea?

Answer 16

Left of tracheal bifurcation, in front of L bronchus

Question 17

What is the blood supply to the trachea?

Answer 17

Inferior thyroid arteries and bronchial arteries - venous drainage to inferior thyroid plexus

Question 18

What is the structure of the trachea?

Answer 18

15-20 C-shaped cartilages, bound by transverse muscles posteriorly. Has pseudostratified columnar epithelium with goblet cells and mucous glands

Question 19

Describe the course of the phrenic nerve

Answer 19

Passes down middle mediastinum but trys to get as lateral as possible.
R phrenic sits between pleura and R BCV, SVC, RA, IVC and passes through central tendon with IVC
L phrenic lies between pleura and L CCA, L SCA, crosses aortic arh lateral to superior intercostal vein, over LV to apex and pierces diaphragm though muscle.
Both give off anterior, lateral and posterior branches to diaphragm from underside

Question 20

What vessel supplies the phrenic nerve?

Answer 20

Pericardiocophrenic artery (branch of internal thoracic)

Question 21

What nerve roots is phrenic artery?

Answer 21

C3,4,5 - mainly C4

Question 22

Describe the course of the vagus nerve

Answer 22

Runs in middle mediastinum and tries to get to midline.
R Vagus - in contact with trachea
L Vagus - held off trachea by great arteries, crosses arch medial to superior intercostal vein
Each passes down behind lung root with supply to pulmonary plexus then reach midline by forming oesphageal plexus

Question 23

Where does the recurrent laryngneal nerve arise?

Answer 23

R RLN - arises from vagus at root of neck and hooks around R SCA
L RLN - arises from vagus as it passes over arch of aorta. Hooks around ligamentum arteriosum.

Question 24

What do the recurrent laryngeal nerves supply?

Answer 24

Whole trachea
Adjacent oesophagus
Most importantly supply muscles of larynx