Posterior mediastinum

Question 1

Boundaries of the posterior mediastinum

Answer 1

Anteriorly- posterior pericardium.

Laterally- mediastinal pleura.

Inferiorly- diaphragm

Posteriorly: T5-12

Superiorly: Thoracic transverse plane

Question 2

Contents of the posterior mediastinum

Answer 2

Oesophagus

Thoracic aorta (part of descending aorta).

Sympathetic trunk- Splanchnic nerves

Azygos veins

Vagus nerve

Thoracic duct

Question 3

Azygous vein

Answer 3

Drains thoraco-abdominal wall on the right.

Ascends from the aortic hiatus- draining the from the abdominal walls and viscera.

Joins with the right subcostal vein (12th intercostal vein).
Posterior ICV II-XI, bronchial veins and the vertebral plexus drains into it as you ascend.

Arches of the root of the right lung and joins into SVC at T5/

The first right intercostal vein drains into the right brachiocephalic vein.

Receives from the hemiazygos vein at T9 and from the accessory hemiazygos T7-8.

Question 4

Hemiazygous veins

Answer 4

Drains the thoraco-abdominal walls on the left.

Forms when the left ascending lumbar veins join with the left subcostal vein above the aortic hiatus.

Ascends posterior to the thoracic aorta. The left posterior ICV at T9-11 drain into it.

The hemiazygos vein drains into the azygos vein at T9.

Question 5

Accessory hemiazygos vein

Answer 5

Left posterior intercostal veins T4-8 drains to this vein and descends.

The vein then crosses between T7 and T8 into the azygos vein on the right.

The top 3 left intercostal veins drain into the left brachiocephalic vein.

Question 6

Thoracic aorta

Answer 6

Descends left of vertebrae t5-12 and oesophagus.

Enters aortic hiatus in the diaphragm, into the abdomen at T12.

Branches into:
Bronchial artieries
Posterior intercostal arteries (and subcostal arteries).
Oesophageal arteries
Pericardial 
Superior phrenic

Question 7

Branches of the thoracic aorta

Answer 7

Branches into all the posterior intercostal arteries- including the subcostal arteries.

Oesophageal arteries.

Paired bronchial arteries.

Superior phrenic- the diaphragm.

Pericardial

Question 8

Thoracic duct

Answer 8

Largest lymphatic vessel originating from the cisterna chyli at L2.

Drains from all parts of the body except:
The head (right)
Neck (right)  
Upper limbs
Right thorax

Passes through aortic hiatus, anterior to the thoracic vertebrae.

Ascends through superior mediastinum and drains at left venous angle

Question 9

Oesophagus

Answer 9

Hollow smooth muscle tube that descends from the superior mediastinum at C6, to the stomach at T11.

It is posterior to the trachea, left atrium, aorta- and right to the aorta.

Veers slightly to the left before entering oesophageal hiatus at T10.

Becomes anterior to the abdominal aorta when it enters the stomach.

Question 10

Innervation of the oesophagus

Answer 10

Vagus nerve- CNX

Oesophageal plexus- via upper thoracic splanchnic nerves (sympathetic trunk)

Question 11

Right vagus nerve

Answer 11

Descends the superior mediastinum, posterior to the sternoclavicular joint.

A branch loops inferiorly, under the right subclavian artery and ascends between the trachea and oesophagus to the larynx.

This loop forms the recurrent laryngeal nerve.

The rest of the right vagus nerves descends to the right of the trachea and posterior to the R.brachiocephalic veins and lung root.

Question 12

Left vagus nerve

Answer 12

As it descends into the left superior mediastinum- forms left recurrent laryngeal nerve.

The left recurrent laryngeal nerve hooks inferiorly to the aortic arch and lateral to ligamentum arteriosum.

Ascends between trachea and oesophagus to the supply the trachea.

Rest of the left vagus nerve descends posteriorly to the lung root.

Question 13

Sympathetic chain

Answer 13

An entire chain of sympathetic nerves running laterally on each side of the vertebral column.

In the thoracic spine there is a ganglion per spinal nerve–> intercostal nerves.

Question 14

The upper thoracic splanchnic nerves

Answer 14

The upper 5 ganglia in the sympathetic trunk.

White rami communicantes enter the trunk via intercostal nerves and synapse at the ganglion—–> fibres are preganglionic.

Grey rami communicantes leave ganglion to form 3 plexi:
Oesophageal
Pulmonary
Cardiac

These nerves also carry afferent fibres from the thoracic viscera, to the brain.

Question 15

The lower splanchnic nerves

Answer 15

The lower 7 ganglia of the sympathetic trunk.

The preganglionic fibres leave the spinal cord but does not synapse at ganglia—- Straight to abdominal viscera.

Forms 3 lower splanchnic nerves:
Greater splanchnic
Lesser splanchnic
Least splanchnic

These nerves descend medially, across the vertebral bodies and enter the abdomen via the crura.

These nerves also carry afferent fibres from the abdominal viscera.

Question 16

Greater splanchnic nerves

Answer 16

Part of the sympathetic trunk.

Formed from the merging of preganglionic fibres from T5-9.

Question 17

Lesser splanchnic nerves

Answer 17

Part of the sympathetic trunk, located in the lower splanchnic nerves.

Arising from the ganglia at the T10-11 regions.

Question 18

The least splanchnic nerves

Answer 18

Part of the sympathetic trunk, part of the lower splanchnic nerves.

Arises from the ganglia from the T12 level.

Question 19

Thoracic referred pain

Answer 19

Due to the upper thoracic splanchnic nerves containing afferent fibres from the thoracic viscera, pain can be referred to different dermatomes.

For example pain from the heart can be sensed by T1. This is sensed in the T1 dermatome- internal, medial half of the arm and hand. Hence why pain from an MI can spread down the arm