Mediastinum
Mediastinum
• central structures between two pleural
sacs, sternum & vertebral bodies
Mediastinum
• Region
• 1. superior mediastinum: behind manubrium (pleura are
apart here)
– thymus gland - most anterior structure, behind manubrium
– in front of brachiocephalic vein, aortic arch
– slowly shrinks w age (largest in childhood), replaced largely by
adipose
• 2. inferior: separation from superior is at line between
sternal angle & intervertebral disc 4- 5
a. anterior - in front of pericardium (thin space)
b. middle - contains pericardium, phrenic nerves, blood
vessels
c. posterior - behind pericardium
Vessels
• arch of the aorta - opposite arch of
azygos, just superior to root of left lung
– thoracic aorta: ascending - arch - descending
aorta - posterior to root of right lung, arteries
exit superiorly from arch:
– brachiocephalic artery
• brachiocephalic artery then divides to right
common carotid and right subclavian aretry
– Left common carotid
– Left subclavian artery
1. Brachiocephalic Artery
2. Carotid Artery, Left
3. Subclavian Artery, Left
4. Aortic Arch
5. Ascending Aorta
6. Pulmonary Trunk
7. Pulmonary Artery, Left
8. Pulmonary Vein, Left
9. Atrim, Left
10. Bicuspid Valve
11. Aortic Semilunar
Valve
12. Ventricle, Left
13. Interventricular
Septum
14. Ventricle, Right
15. Papillary Muscle
16. Chordae Tendinae
17. Tricuspid Valve
18. Atrium, Right
19. Pulmonary
Semilunar Valve
20. Superior Vena Cava
Veins
• superior & inferior vena cava - entering the
right atrium = junction of brachiocephalics
• brachiocephalic veins - continuous with
superior vana cava superiorly, behind
sternoclavicular joint
– a. combination of subclavian & internal jugular
veins
– b. internal thoracic veins also drain into
brachiocephalics
Blood vessels
• Pulmonary trunk
– Pulmonary trunk: short, just left of aortic arch branches to Right, Left pulmonary artery
- ligamentum arteriosum - residual of ductus
arteriosum - connects to aorta in fetal
circulation
– Azygos vein
Other structures
• Other structures in mediastinum
– Trachea - behind right brachiocephalic vein
– Esophagus - behind trachea
Nerves
• phrenic nerve: in mediastinal pleura on each side,
anterior to roots of lungs
– anterior to subclavian artery, parallels internal thoracic artery
– adjacent to brachiocephalic veins, superior vana cava or aorta,
pericardium; to diaphragm
• vagus nerves: posterior to phrenics
– Right vagus - between brachiocephalic artery & vein
– Left vagus - between left common carotid & subclavian artery
– recurrent laryngeal branch of left vagus - curls under aortic arch
behind ligament arteriosum
– recurrent laryngeal branch of right vagus - curls under the
subclavian artery
Plexus from Vagus
• Cardiac plexus: 2 portions
– superficial - just under aortic arch; & deep - posterior to arch,
anterior to trachea (gets most branches)
comprised of branches of sympathetic trunks:
– 3 cervical cardiac branches - from neck, thru inlet to superior
Mediastinum
– several thoracic branches
• Pulmonary plexuses: 4 - R & L anterior & posterior
– in front & behind pulmonary artery on each side, at root of lungs
– from there into lungs
– nerve filaments arise as branches from cardiac plexus
• Coronary plexus - nerve filaments also come from
cardiac plexus
- to heart, follow coronary arteries
Pericardial Sac
• Serous Pericardium - serous membrane double layer
– a. visceral pericardium - forms epicardium - outer
covering of heart
– b. parietal pericardium - thicker, tougher than pleura
– c. pericardial cavity
• Fibrous pericardium - dense fibrous CT - fused
with parietal serous pericardium continuous with
deep fascia of neck also attaches to diaphragm
below & to esophagus & aorta posteriorly
Pericardiocentesis