Superior & Posterior Mediastinum

Question 1

What is the course of the aorta?

Answer 1

• ascending aorta as it comes out of LV
  
  • gives rise to R & L coronaries
• arch goes upwards, backwards to the left (superior mediastinum)
  
  • begins and ends at manubriosternal – T4/T5
  • arches over:
    
    • L pulm artery
    • L pulm veins
    • L main bronchi
    • branching of pulmonary trunk (connected to it via ligamentum arteriosum)
• becomes descending thoracic aorta
• descends midline behind oesophagus and anterior to VC
• enters diaphragm thru aortic hiatus between the crura @T12

Question 2

What are the major branches of the aorta?

Answer 2

• First brances are R & L coronares off ascending
• Arch supplies head, neck, and upper limb
• Brachiocephalic trunk: –> R subclavian & R carotid
• L carotid
• L subclavian

Descending thoracic aorta gives off:

• posterior intercostal arteries
• bronchial areteries @ hilum of lungs
• oesophageal branches
• minor pericardial branches

Question 3

What are the contents of the superior mediastinum?

Answer 3

Superficial to deep:

• thymus (if present)
• great veins
• aortic arch + vagus and phrenic nerves
• trachea
• oesophagus
• thoracic duct
• L recurrent laryngeal nerve

Question 4

What are the contents of the posterior mediastinum?

Answer 4

Superior posterior:

• trachea
• oesophagus
• R & L recurrent laryngeal nerves
• thoracic duct (on back of oesophagus)

Deep posterior:

• descending thoracic aorta
• oesophageus (vagal plexus on front, thoracic duct on back)
• azygous vein
• sympathetic trunks

Question 5

What is the origin and course of the jugular veins?

Answer 5

• drain the head and neck
• into subclavian vein (drains upper limb)
• into brachiocephalic veins (@medial clavicle)
• which join into SVC (@1st R costal cartilage)

Question 6

What is the origin and course of the subclavian veins?

Answer 6

• drain the upper limb
• receive drainage from head and neck via IJVs
• drain into brachiocephalic veins (@medial clavicles)
• which form the SVC (@1st R costal cartilage)

Question 7

What is the origin and course of the brachiocephalic veins?

Answer 7

• drainage from IJV –> subclavians
• subclavians branch @ medial clavicle
• form SVC (@1st R costal cartilage)
• R brachiocephalic is shorter and more vertical
• L brachiocephalic crosses over to left (@1st R costal cartilage)

Question 8

What is the origin and course of the superior vena cava?

Answer 8

• Brachiocephalic veins join (@1st R costal cartilage)
  
  • drainaige from IJVs > subclavians > brachiocephalics
• SVC enters peridcardium @2nd R costal cartilage
• SVC enters RA @3rd R costal cartilage
• venous return from head, neck, and upper limbs

Question 9

What is the azygous system of veins?

Answer 9

• ascends the R vertebral column arching over the R lung root
• enters SVC posteriorly @ 2nd R costal cartilage
• venous return from
  
  • posterior intercostal veins
  • thoracic walls
  • everything in thorax except heart
  • draining descending aorta supply:
    
    • bronchial, oesophageal, pericardial veins

Question 10

What is the course of the trachea?

Answer 10

• extends through superior mediastinum at T4/T5
• splits into R & L main bronchi

Question 11

What is the course of the oesophagus?

Answer 11

superior mediastinum:

• posterior to trachea
• descends midline

posterior mediastinum:

• passes left into diaphragm thru oesophageal hiatus @ T10
• in front of descending aorta and VC

Question 12

What is the course of the thoracic duct?

Answer 12

• begins at cisterna chyli
  
  • distal end, drains lymph from intestinal trunk and lumbar trunks
  • posterior to abdominal aorta on anterior L1 & L2
• collects all lymph from below the diaphragm (pelvis, abdomen, lower limbs)
• always on the back of the oesophagus, anterior to aorta & VC
• ascends upwards and empties into junction at L IJV and L subclavian vein

Question 13

What is the course of the R vagus nerve?

Answer 13

• cranial nerve
• runs in carotid sheath (int. carotid and jugular vein)
• runs medially, alongside trachea (phrenic lateral)
• behind lung root (phrenic anterior)
• to anterior oesophagus
  
  • joins w/L vagus to form an oesophageal nerve
• gives off R recurrent laryngeal nerve @ R subclavian artery
  
  • hooks around the artery and ascends the right tracheoesophageal groove to innervate larnyx

Question 14

What is the course of the L vagus nerve?

Answer 14

• cranial nerve
• runs in carotid sheath (int. carotid and jugular vein)
• lateral to aortic arch (can’t get to trachea)
• behind lung root (phrenic anterior)
• onto anterior oesophagus
  
  • meets R vagus to form an oesophageal nerve
• gives off L recurrent laryngeal nerve at arch of aorta
  
  • hooks around ligamentum arteriosum
  • under arch of aorta
  • back to laryngeal structures in the L tracheoesophageal groove

Question 15

What is the course of the phrenic nerve?

Answer 15

• branch of cervical plexus (ventral rami C3, 4, 5)
• descends on scalenus anterior
• passes between subclavian artery and vein
• passes anterior to the lung root (bronchi & pulm vessels)
• pierces and innervates the diaphragm
  
  • R thru caval orifice @ T8
  • L into muscle of L dome
• R is lateral to venous structures (SVC, RA, IVC)
• L is lateral to arterial structures (aortic arch, LV)

Innervation:

• motor: abdominal surface of diaphragm
• sensory: mediastinal & diaphragmatic pluera, pericardium

Question 16

What are the borders of the superior mediastinum?

Answer 16

• above line from mediasternal junction to T4/T5
• between the L & R pleural cavities

Question 17

What are the borders of the inferior mediastinum?

Answer 17

• below mediasternal junction – T4/45
• middle contains heart
  
  • divides inferior mediastinum into anterior and posterior mediastinum

Question 18

What can be a cause of dysphasia (difficulty swallowing)?

Answer 18

4 aortic branches (i.e. no brachiocephalic trunk)

traps trachea & oesophageus in centre