posterior mediastinum

Question 1

what are the boundaries of the posterior mediastinum

Answer 1

Anterior – posterior pericardium 
Posterior vertebrae T5-12
Lateral – mediastinal pleura 
Superior – transverse thoracic plane 
Inferior – diaphragm

Question 2

what are the contents of the posterior mediastinum

Answer 2

Oesophagus 
Thoracic aorta
Azygous system of veins 
Thoracic duct 
Vagus nerve
Sympathetic trunk 
Splanchnic nerves

Question 3

what are autonomic nerves

Answer 3

preganglion ganglion post ganglion
Sympathetic – paravertebral chain or prevertebral (pre-aortic) ganglia
Short preganglionic and short post ganglionic, PS opposite
Parasympathetic - terminal/intramural ganglia

Question 4

what do sympathetic and parasympathetic nerves do

Answer 4

Sympathetic- thoracolumbar outflow T1 to L2

Parasympathetic -craniosacral outflow: some cranial nerves (including vagus nerves) and S2, S3, S4

Question 5

what is the sympathetic trunk

Answer 5

Vertical chain of sympathetic nerves running entire length of the vertebral column
Located on both sides of the vertebral bodies
Paravertebral (chain) ganglia located along its length
In the thoracic spine usually one ganglion per spinal level, more sparse in lumbar region

Question 6

what are the spinal nerve levels T1-T4/5

Answer 6

Preganglionic sympathetic fibres leave the spinal nerve (white rami communicantes) and synapse at the paravertebral ganglion
Postganglionic sympathetic fibres leave the ganglion (grey rami communicantes) and pass to the pulmonary, cardiac and oesophageal plexi
These nerves also carry afferent fibres (carrying sensory information) from the thoracic viscera, they supply back to the brain

Question 7

What are dermatomes and referred pain

Answer 7

Dermatome – area of skin supplied by a single spinal cord level or spinal nerve
Pain from heart can be felt down arm and across chest from T1-T4/5
The sensory supply to diaphragm partially carried by the phrenic nerve so pain can be felt at the shoulder

Question 8

what are the spinal nerve levels T5/6-T12

Answer 8

Sympathetic trunk – spinal nerve levels T5/6-T12
Preganglionic sympathetic fibres leave the spinal cord (white rami communicantes) and enter the ganglion but don’t synapse
Preganglionic sympathetic fibres leave these ganglia and synapse in the prevertebral (pre-aortic) ganglia before passing to the abdominal viscera
These form 3 splanchnic nerves

Question 9

What are the splanchnic nerves

Answer 9

1 greater splanchnic nerves arise from levels T5-9
2 lesser from T10-11
3 least T12
Descend medially from ganglia across vertebral bodies and enter abdomen by piercing the diaphragm
Carry preganglionic sympathetic fibres to and visceral afferent fibres from the abdominal viscera

Question 10

what is the vagus nerve

Answer 10

Enters superior mediastinum posterior to sternoclavicular joint
The left and right recurrent laryngeal nerves branch from it but have differing courses
Continues into posterior mediastinum and contribute to pulmonary, cardiac and oesophageal plexuses
Parasympathetic supply
Preganglionic fibres until they reach the plexus

Question 11

what is the right vagus

Answer 11

Right recurrent laryngeal branch hooks under the right subclavian artery and ascends between trachea and oesophagus
Supplies larynx
Right vagus nerve continues posterior to right of the trachea, posterior to right brachiocephalic vein and lung root/hilum

Question 12

what is the left vagus

Answer 12

Left recurrent laryngeal nerve hooks inferiorly to the aortic arch, immediately lateral to ligamentum arteriosum
Ascends similarly to the right nerve supply to the larynx
Rest of left vagus nerve runs posteriorly to the lung root

Question 13

what is the thoracic aorta

Answer 13

Continuous with arch of aorta
Descend to left side of vertebrae T5-T12
Oesophagus positioned to its right
Terminates at vertebral level T12 where it enters the abdomen through the aortic hiatus in the diaphragm
Thoracic duct and azygous veins ascend on its right and also pass through diaphragm at aortic hiatus

Question 14

what are the branches of the thoracic aorta

Answer 14

Paired
1 posterior intercostal
2 subcostal
3 bronchial – R is 3rd posterior intercostal artery and L from descending aorta
4 superior phrenic – arch over to top of diaphragm

Unpaired
A pericardial
B oesophageal
C mediastinal

Question 15

what is the azygous system of veins (RHS)

Answer 15

1st intercostal vein drains into brachiocephalic veins
T2-4 drain into superior intercostal vein which drains into azygous
Azygous formed by subcostal and ascending lumbar veins, connect to T5-T11
Drains blood into right atrium via superior vena cava

Question 16

what is the azygous system of veins (LHS)

Answer 16

Hemi azygous drains T9-T11
Accessory hemi-azygous drains T5-T8
T1-4 form superior intercostal vein to drain into left brachiocephalic

Question 17

what is the azygous vein

Answer 17

Arises on right side by junction of subcostal (T12 level) and ascending lumbar veins
Drains deoxygenated blood from the posterior thoraco-abdominal walls and viscera
Tributaries- posterior intercostal veins (levels T5-T11), bronchial veins and vertebral venous plexus
Arches over root of right lung to join SVC
Usually receives blood from hemiazygos veins which drain on left side
Forms a collateral pathway between SVC and IVC

Question 18

what are semi-azygous veins

Answer 18

Arises on left side by junction of subcostal (T12) and ascending lumbar veins
Ascends on left side posterior to aorta draining left posterior intercostal veins (T9-11)
Crosses to right and joins azygos
Accessory hemi-azygos drains levels T5-8 on left side
Crosses T7/8 to join azygos and sometimes joins hemi-azygos

Question 19

what is the thoracic duct

Answer 19

Largest lymph channel
Conveys all lymph from body except head, neck, upper limb and thorax on right side
Originates in cisterna chyli in abdomen (L2)
Ascends through the aortic hiatus passing anterior to thoracic vertebrae
Ascends into superior mediastinum and drains into venous system at the left venous angle (junction of internal jugular and subclavian veins)

Question 20

what is the oesophagus

Answer 20

Descends from superior mediastinum posterior to the trachea
Muscular tube
Passes posterior and to the right of the aorta
Veers slightly left before piercing through diaphragm
Becomes anterior to abdominal aorta before entering the stomach
Innervation: CNX and sympathetic trunk via oesophageal plexus

Question 21

what are the 3 constrictions of the oesophagus

Answer 21

Arch of aorta
Left main bronchus
Diaphragm