Superior mediastinum

Question 1

Describe the borders of the superior mediastinum

Answer 1

Superiorly- superior thoracic inlet (T1, jugular notch, clavicle)

Posteriorly- T1-T4/T5

Laterally- mediastinal pleura

Anteriorly- manubrium

Inferiorly- Transverse thoracic plane

Question 2

State the visceral content of the superior mediastinum

Answer 2

Try to eat the soup and vitamin noodles

1. Thymus
2. Thoracic duct
3. Eosophagus
4. Sympathetic trunk
5. Ascending aorta
6. Veins- SVC, Bracheocephalic, Left superior intercostal vein
7. Nerves- Vagus and phrenic

Question 3

Describe the thymus and its supply and drainage

Answer 3

Immediately deep from manubrium
Lymphoid organ
Atrophies during puberty (variable size in adults, mostly fat)
Important in building immune system in infancy

Arterial supply: internal intercostal arteries
Venous drainage: Left brachiocephalic vein/ internal intercostal vein

Lymph drainage: parasternal nodes, tracheobronchial nodes, nodes in root of neck

Question 4

Describe the brachiocephalic veins

Outline its venous tributaries

Answer 4

Immediately posterior to thymus
Drain into superior vena cava

RHS
vertebral
1st posterior intercostal
internal thoracic veins
LESS: inferior thyroid and thymic veins

LHS
vertebral
1st posterior intercostal
Left superior intercostal
Inferior thyroid 
Internal thoracic veins
LESS: thymic and pericardial veins

Question 5

Why is the left bracheocephalic vein less protected in children?

Answer 5

In adults it cross the midline posteriorly to the manubrium

In children it passes above it

Question 6

Describe the superior intercostal vein

Answer 6

Receives from 2-4th posterior intercostal vein, left bronchial veins and left pericardiophenic vein

Passes over left side of aortic arch lateral to left vagus nerve, medial to left phrenic nerve

Inferiorly may connect with accessory hemiazygos vein

Question 7

Describe the superior vena cava

What is its clinical relevance?

Answer 7

Root is protected by pericardium

Venous tributaries include the azygos veins (immediately before entering pericardium), sometimes pericardial and mediastinal veins

Easily visualised forming right superolateral border of mediastinum on CXR

Question 8

Describe the arch of the aorta

Answer 8

Gives of three branches : bracheocephalic, left common carotid (supplies right head and neck), left subclavian

Intially anterior to trachea than passes laterally

Question 9

What is the ligamentus arteriosum?

Answer 9

Patent vessel

Embryologically “ductus arteriosium” used to bypass non-functioning lungs

Question 10

How could the position of the trachea and oesophagus shift?

Answer 10

Swallowing
Breathing
Disease
Use of specialised instruments

Question 11

Describe the vagus nerve

Answer 11

Provides parasympathetic innervation to thoracic viscera and carries visceral afferents from thoracic viscera

Right vagus lies between BC trunk and BCV
Hooks behind trachea as it bifurcates
gives off branches to oesophageal, cardiac and pulmonary plexi
Supplies larynx

Left vagus enters between LCCA and LSA
Also gives rise to left recurrent laryngeal nerve at inferior margin of aortic arch, lateral to ligamentus arteriosum
Runs posteriorly to hilum

Question 12

What do visceral afferents do?

Answer 12

Relay information to CNS about normal physiological process and reflexes
NOT PAIN

Question 13

Describe briefly the phrenic nerves

Answer 13

Arise from C3,C4,C5
Supply motor and sensory innervation to diaphragm and associated membranes
Provide somatic afferent innervation fibres to mediastinal pleura, fibrous pericardium and parietal layer of serous pericardium

Question 14

Describe the right phrenic nerve

Answer 14

Runs laterally to R.vagus
Accompanied by pericardiacophrenic vessels into fibrous pericardium
Passes through diaphragm with IVC

Question 15

Describe the left phrenic nerve

Answer 15

Lateral to L.vagus
Passes over aorta
Accompanied by pericardiacophrenic vessels into fibrous pericardium
Leaves thorax through diaphragm near apex of heart