Thoracic inlet and superior mediastinum

Question 1

What are the borders of the thoracic inlet?

Answer 1

• Anterior: Manubrium
• Lateral: 1st rib and costal cartilage
• Posterior: 1st thoracic vertebrae

Question 2

Why is the 1st rib atypical?

Answer 2

• Head articulates with body and transverse process 1st thoracic vertebrae only.
• 1st chondrosternal joint is immobile primary cartilaginous joint.

Question 3

What are the structures that pass through the thoracic inlet?

Answer 3

Arteries:
- Left/right subclavian artery
- Left/right common carotid artery
Veins:
- Left/right subclavian vein
- Left/right internal jugular vein
- Left/right brachiocephalic vein
Nerves:
- Phrenic nerves 
- Vagus nerves
- Recurrent laryngeal nerves
- Sympathetic trunks
Other structures:
- Apex of the lungs 
- Trachea
- Oesophagus
- Thoracic duct

Question 4

What are the boundaries of the superior mediastinum?

Answer 4

• Superior: Thoracic inlet

- Inferior: Plane crossing through the manubriosternal joint and T4/T5 intervertebral disc

Question 5

What are the origins of the brachiocephalic veins?

Answer 5

• Behind the sternoclavicular joint

- Convergence of the subclavian and internal jugular veins

Question 6

What is the origin of the SVC?

Answer 6

• Behind lower border of right 1st costal cartilage

- Convergence of the brachiocephalic veins

Question 7

What is the relationship between the brachiocephalic veins?

Answer 7

The left brachiocephalic vein is longer than the right.

Question 8

What are the relationships of vessels at the thoracic inlet?

Answer 8

• The subclavian veins lie anterior to the subclavian arteries.
• Scalene anterior lies between the 2 vessels.
• The common carotid arteries lie medial to the internal jugular veins.

Question 9

What are the veins of the superior mediastinum?

Answer 9

• Left/right brachiocephalic vein
• Superior vena cava
• Superior intercostal veins

Question 10

Where does the azygos vein join the SVC?

Answer 10

Level of T4 vertebrae

Question 11

What are the branches of the aortic arch?

Answer 11

• Brachiocephalic trunk
• Left common carotid artery
• Left subclavian vein

Question 12

What are the boundaries of the aortic arch?

Answer 12

• Beginning/end: T4/T5 level.

- Superior-most extent: T3/T4 level.

Question 13

What is the ligamentum arteriosum and its attachments?

Answer 13

• The ligamentum arteriosum is the remnants of the ductus arteriosus.
• It is attached to the ishmus of the aortic arch (last section of the arch, where origin of left subclavian artery is), and the pulmonary trunk.

Question 14

Where is the bifurcation of the brachiocephalic trunk?

Answer 14

Upper border of sternoclavicular joint

Question 15

What are the branches of the subclavian artery?

Answer 15

• Vertebral artery
• Internal thoracic artery
• Thyrocervical trunk
• Costocervical trunk

Question 16

What are the relations of the vertebral artery?

Answer 16

• Enters the transverse foraman of C6 vertebrae.
• Ascends up the spinal cord, sending branches to the vertebrae and spinal cord.
• It joins with other vertebral artery to form the basilar artery supplying cerebellum and occipital lobe.

Question 17

What are the relations of the internal thoracic artery?

Answer 17

• Descends on the internal thoracic wall lateral to the sternum.
• Gives rise to anterior intercostal arteries.

Question 18

What are the terminal branches of the internal thoracic artery?

Answer 18

• Musculophrenic artery

- Superior epigastric artery

Question 19

What are the branches of the thyrocervical trunk?

Answer 19

• Inferior thyroid artery
• Ascending cervical artery
• Suprascapular artery
• Transverse cervical artery

Question 20

What are the branches of the costocervical trunk?

Answer 20

• Posterior intercostal artery: Supplies posterior intercostal arteries to upper 2 intercostal spaces.
• Deep cervical artery: Supplies deep structures of the neck.

Question 21

What are the terminal branches of the external carotid artery?

Answer 21

• Superficial temporal artery

- Maxillary artery

Question 22

What are the 2 lymphatic vessels in the thorax?

Answer 22

• Right lymphatic trunk

- Thoracic duct

Question 23

Where does the thoracic duct drain?

Answer 23

Junction of the left internal jugular and subclavian veins.

Question 24

What are the relations of the nerves at the thoracic inlet?

Answer 24

• All nerves lie anterior to the subclavian arteries and posterior to the subclavian veins.
• The phrenic nerves lies lateral to the vagus nerves.

Question 25

What are the relations of the phrenic nerves?

Answer 25

• The right phrenic nerve descends to the right of the SVC, anterior to the right bronchus and on the fibrous pericardium overlying the right atrium.
• The left phrenic nerve descends anterior to the apex of the lungs and the left bronchus, then on the fibrous pericardium overlying the left ventricle.

Question 26

What are the relationships of the vagus nerves?

Answer 26

• The right vagus nerve descends posterior to the right bronchus and forms the anterior vagal trunk of the oesophageal plexus.
• The left vagus nerve descends posterior to the left bronchus and forms the posterior vagal trunk of the oesophageal plexus.

Question 27

What are the relationships of the recurrent laryngeal nerves?

Answer 27

• The right recurrent laryngeal nerve originates from the right vagus nerve just inferior to the bifurcation of the brachiocephalic trunk.
• The left recurrent laryngeal nerve originates from the left vagus nerve at the level of the aortic arch and winds around to posterior aspects of the aortic arch.
• Both recurrent laryngeal nerves ascend in the tracheo-oesophageal groove.

Question 28

What is the function of the recurrent laryngeal nerves?

Answer 28

Innervates all the intrinsic muscles of the larynx (involved with swallowing), except the cricothyroid muscles.