Superior Mediastinum

Question 1

Location

Answer 1

Middle septum
Central compartment of thorax
Located between left &
right pleural cavities

Question 2

Boundaries

Answer 2

Superior limit marked by the superior thoracic aperture: [manubrium, 1st rib and costal cartilage, T1 vertebra]
Inferior limit marked by the Transverse thoracic plane: [Sternal angle to vertebral level T4/T5]
Anterior: Manubrium
Posterior: T1-T4/5 vertebral bodies
Lateral: Mediastinal pleura

Question 3

Contents

Answer 3

Arteries (arch of aorta and branches)
Veins (brachiocephalic veins, superior vena cava)
Trachea
Oesophagus
Thoracic duct
Phrenic and Vagus nerves
Thymus gland (part)

Question 4

Thymus gland

Answer 4

Lymphoid organ
Lymph drains through from parasternal, brachiocephalic and tracheobronchial nodes
After puberty atrophies and replaced by fat
Supplied internal thoracic arteries

Located immediately deep to the sternum in
Superior AND Anterior Mediastinum

Question 5

Aortic arch has 3 branches

Answer 5

Brachiocephalic trunk
Left common carotid artery
Left subclavian artery

Question 6

Aorta branches

Answer 6

1st: Ascending - Left & Right coronary arteries
2nd: Arch - Brachiocephalic trunk, Left common carotid & Left subclavian arteries
3rd: Descending – Intercostal & Lumbar arteries

Question 7

Veins in Superior Mediastinum

Answer 7

Superior Vena Cava formed by union of the Left brachiocephalic vein and Right brachiocephalic vein
Each Brachiocephalic vein is formed by the union of an Internal jugular vein and a Subclavian vein

Question 8

Ligamentum Arteriosum

Answer 8

Embryological remnant of the Ductus Arteriosus: an open duct connecting the pulmonary trunk and the arch of aorta.
Important in fetal circulation allowing blood to bypass the immature lungs.

Closes at birth and remains in the adult as a ligamentous structure.

Question 9

Trachea

Answer 9

Tube C-shaped cartilage rings
Trachealis muscle runs posteriorly
Runs from Larynx to Bronchi

Question 10

Oesophagus

Answer 10

Muscular tube
Runs from Pharynx to stomach

The Thoracic duct and the
Oesophagus pass through the
Superior AND Posterior Mediastinum

Question 11

Thoracic Duct

Answer 11

Transports lymph to venous system
Receives multiple branches throughout thorax
Numerous lymph nodes associated with thoracic aorta

The Thoracic duct and the
Oesophagus pass through the
Superior AND Posterior Mediastinum

Question 12

Phrenic nerves

Answer 12

Originate from the anterior rami of spinal nerves C3, C4 & C5

Sole motor supply of diaphragm
1/3 of the sensory supply to diaphragm (central region)

There are 2, right and left

Enter superior mediastinum between brachiocephalic veins and subclavian arteries
Pass anterior to main bronchi

Question 13

Vagus Nerve

Answer 13

Cranial nerves (CNX) hence originate from the brainstem
There are 2, right and left
Each enters the Superior Mediastinum close to but medial to the Phrenic nerve
Each gives rise to a Recurrent Laryngeal branch to supply the larynx
Continues into the Posterior Mediastinum coursing posterior to the main bronchi
Provide parasympathetic supply via pulmonary, cardiac and oesophageal plexi

Question 14

Anterior mediastinum

Answer 14

Narrow cavity containing:
Thymus gland in children which atrophies in the adult and is replaced by fatty tissue
Pericardial-sternal ligaments
Lymph nodes and vessels
Internal thoracic artery

Boundaries:
Sternum anteriorly
Pericardial sac posteriorly
Diaphragm inferiorly

Question 15

Pass anterior to main bronchi

Answer 15

Phrenic nerve