Superior Mediastinum

Question 1

Where is the mediastinum

Answer 1

Middle septum
Central compartment of thorax
located between left and right pleural cavities

Question 2

Divisions

Answer 2

divided into superior and inferior at the level of sternal angle T4/5

Question 3

Inferior mediastinum

Answer 3

Anterior, middle, posterior

Question 4

Boundaries of superior mediastinum: Superior limit

Answer 4

Limit marked by superior thoracic aperture: manubrium, 1st rib and costal cartilage, T1 vertebrae

Question 5

Boundaries of superior mediastinum: Inferior limit

Answer 5

Marked by transverse thoracic plane: Sternal angle to vertebral level T4/5

Question 6

Boundaries of superior mediastinum: Anterior

Answer 6

Manubrium

Question 7

Boundaries of superior mediastinum: Posterior

Answer 7

T1-T4/5 vertebral bodies

Question 8

Boundaries of superior mediastinum: Lateral

Answer 8

Mediastinal pleura

Question 9

Contents

Answer 9

Arteries (arch of aorta and branches)
Veins (Branchiocephalic veins, superior vena cava)
Distal part of trachea
Oesophagus
Thoracic duct
Phrenic and Vagus nerves (left and right)
Thymus gland

Question 10

Thymus gland

Answer 10

Located immediately deep to the sternum in superior and anterior mediastinum
Lymphoid organ (lymphatic system)
Lymph drains through from parasternal, brachiocephalic and tracheobronchial nodes
After puberty atrophies and replaced by fat
Supplied internal thoracic arteries
B and T lymphocytes (T matures in thymus)

Question 11

Aortic Arch

Answer 11

3 branches

1. Brachiocephalic trunk - branches into right common carotid and subclavian arteries
2. Left common carotid artery
3. Left subclavian artery

Question 12

Branches of aorta

Answer 12

1st: Ascending
2nd: Arch
3rd: descending

Question 13

Ascending aorta

Answer 13

Right and left coronary arteries

Question 14

Descending

Answer 14

Intercostal and lumbar arteries

Question 15

Veins

Answer 15

Superior vena cava formed by union of left and right brachiocephalic veins
Each brachiocephalic vein is formed by the union of internal jugular vein and a subclavian vein

Question 16

Ligamentum Arteriosum

Answer 16

Embryological remnant of Ductus Arteriosus: an opening duct connecting pulmonary trunk and arch of aorta
Important in foetal circulation allowing blood to bypass the immature lungs
Closes at birth (fibroses) and remains in adult as ligament

Question 17

Trachea

Answer 17

Tube c shape cartilage rings
Trachealis muscle rubs posteriorly
Runs from larynx to bronchi

Question 18

Oesophagus

Answer 18

Muscular tube

Runs from pharynx to stomach

Question 19

Thoracic duct

Answer 19

Transports lymph to venous system
Receives multiple branches throughout thorax
Numerous lymph nodes associated with thoracic aorta
Passes through superior and posterior mediastinum

Question 20

Phrenic nerves

Answer 20

Originates from anterior rami of spinal nerves C3, C4, C5
Sole motor supply of diaphragm
1/3 of the sensory supply to diaphragm - diaphragmatic pleura also get sensory supply
There are 2: right and left
Spans through entire superior mediastinum between brachiocephalic veins and subclavian arteries
Pass anterior to main bronchi
Sticks to pericardium sack

Question 21

Vagus nerves

Answer 21

Cranial nerves so they originate from 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 22

Anterior mediastinum

Answer 22

Is a narrow cavity containing:
Thymus gland that atrophies 
Pericardial - sternal ligaments 
Lymph nodes and vessels 
Internal thoracic artery

Question 23

Boundaries of anterior mediastinum

Answer 23

Sternum anteriorly
Pericardial sac posteriorly
Diaphragm inferiorly