L3.2 Mediastinum

Question 1

Features of the mediastinum

Answer 1

• sits in b/w the central core of the thoracic cavity (b/w lungs)
• Splits into (at the plane of Louis):
  
  • SUP
  • INF
    
    • ANT - b/w heart & body of sternum
    • MIDDLE - heart
    • POS - b/w heart & vertebral column

Question 2

SUP mediastinum structure orders

Answer 2

1. Thymus
2. Veins
3. Arteries
4. Nerves
5. Trachea
6. Oesophagus
7. Thoracic duct

Question 3

SUP mediastinum 1) thymus

Answer 3

• Thymus - immediately deep to sternum
  
  • Development of immune system
  • Redundant after puberty

Question 4

SUP mediastinum 2) Veins

Answer 4

• SVC → formed by L (longer) & R brachio(arm)cephalic(head) V
  
  • ∴internal jugular V & subclavian V drains into brachiocephalic V

Question 5

SUP mediastinum 3) Arteries

Answer 5

• Aorta arches POS & to the L over pulmonary trunk & L main bronchus
• Branches:
  
  • Brachiocephalic trunk → branch to R subclaivn & R common carotid
  • L common carotid
  • L subclavian

Question 6

SUP mediastinum 4) nerves

Answer 6

• Vagus - POS to hilum
• Phrenic - ANT to hilum
• Recurrent laryngeal - branch from vagus N
  
  • Branches starts low → hooks back up at the plane of louis (the definition of recurrent)
    
    • L hooks under arch of aorta (close to ligamentum arteriosum)
    • R hooks under R subclavian A

Question 7

SUP mediatstinum 5) Trachea

Answer 7

• Not divided into L/R main bonchi

Question 8

SUP mediastinum 6) oesophagus

Answer 8

• Passes through the mediastinum

Question 9

SUP mediastinum 7) thoracic duct

Answer 9

• POS to oesophagus → drains into L SC V

Question 10

INF ANT mediastinum

Answer 10

• Fats, lymph node, internal thoracic vessels (directly POS to sternum), INF part of thymus

Question 11

INF MID mediastinum

Answer 11

• Heart
• N passing through the heart (Phrenic - LAT)
• Great vessels

Question 12

INF POS mediastinum

Answer 12

• Vagus, Phrenic N
• Oesophagus (moves twd L)
• Descending aorta (initially L of oesophagus → moves twd midline - POS to oesophagus)
• Thoracic duct ascending
  
  • Directly ANT to body of vertebrae

Question 13

Descending Aorta

Answer 13

• Most of BS to thoracic viscera & Wall
• Branches:
  
  • POS intercostal A → anastomose with ANT intercostals from subclavian A
  • Bronchial A → close to bifurcation → follows bronchi
  • Oesophageal branches

Question 14

Oesophagus

Answer 14

• Thick muscular tube (3 layers of muscles)
• A-P plane is flattened against vertebrae
• BS: from D. aorta
• Venous drainage: Into azygous system
• N supply from: Sym, parasym (vagus) → forms oesophageal plexus

Question 15

Thoracic duct

Answer 15

• Moves to the L at the plane of Louis → drains into L SC V
• All lymph below dia drains into thoracic duct

Question 16

Azygous system

Answer 16

• Series of V on the POS thoracic wall
• Drains into SVC
• Drains:
  
  • Thorax
  • POS intercostal
  • Bronchial V
  • Oesophageal V

Question 17

3 main azygous vessels

Answer 17

1. R azygous V: On R side of vertebrae → ascends on R → arches over R main bronchus → SVC
2. Accessory hemiazygous: drains POS intercostal above T8-9 (L)
3. Hemiazygous: Drains POS intercostal below T8-9 (L)
   
   • Both Accessory & hemiazygous drains into R azygous V at ~T8-9