1. MEDIASTINUM

2. MEDIASTINUM Central compartment of the thoracic cavity
Covered by mediastinal pleura
Contents: all thoracic viscera EXCEPT lungs
Extent:
Superior - thoracic inlet
Inferior - diaphragm
Anterior - sternum & costal cartilages
Posterior- bodies of thoracic vertebrae

3. MEDIASTINUM Surrounded by blood and lymphatic vessels
Lymph nodes, nerves and adipose tissues
Looseness of structures enable mediastinum to accommodate changes in movement, volume & pressure in the thoracic cavity

4. Divisions of the Mediastinum
SUPERIOR MEDIASTINUM
Superior - thoracic inlet
Inferior transverse thoracic plane
Anterior - sternal angle
Posterior - IV disc T4 & T5
INFERIOR MEDIASTINUM
Superior – transverse thoracic plane
Inferior - diaphragm

5. Divisions of the Mediastinum
INFERIOR MEDIASTINUM
a. ANTERIOR MEDIASTINUM
- contains thymus remnant, lymph nodes & fats
b. MIDDLE MEDIASTINUM
- contains the heart & great vessels
c. POSTERIOR MEDIASTINUM
- contains esophagus, great vessels,vagus nerves & symphathetic trunks

6. Superior Mediastinum Contents: (Anterior – Posterior) 1. Thymus gland
- primary lymphoid organ located behind manubrium
- puberty undergoes gradual involution
2. Great Vessels
Brachiocephalic Veins
Superior Vena Cava
- formed at level of 1st right costal cartilage
- enters right atrium at level of 3rd right costal cartilage

9. Superior Mediastinum Contents: Arch of the Aorta
- starts behind 2nd right SC joint
- ends at 2nd left SC joint
Branches:
Brachiocephalic Trunk
Left Common Carotid Artery
Left Subclavian Artery

10. Superior Mediastinum Contents: 3. Nerves Vagus & Phrenic Nerves
Cardiac Plexus of Nerves
Left Recurrent Laryngeal Nerve
4. Trachea
5. Esophagus
6. Thoracic Duct
7. Prevertebral Muscles

16. Anterior Mediastinum Smallest subdivision of the Inferior Mediastinum
Boundaries:
Anterior : body of sternum & trans thoracis muscles Posterior : pericardium
Contents: Loose CT (Sternopericardial Ligament)
Adipose tissue
Lymphatic Vessels & lymph nodes
Branches of Internal Thoracic Vessels

17. Posterior Mediastinum
Boundaries:
Anterior - Pericardium & Diaphragm
Posterior - T5 to T12 vertebrae
Contents:
Thoracic Aorta Esophagus & Plexus
Thoracic Duct Thoracic Sympathetic Trunks
Post Mediastinal LN Thoracic Splanchnic Nerve
Azygos & Hemiazygos Veins

18. Thoracic Aorta Branches: 1. Bronchial Arteries 5. Esophageal Arteries
2. Pericardial Arteries 6. Mediastinal Arteries
3. Post. Intercostal Arteries 7. Subcostal Arteries
4. Superior Phrenic Arteries

19. Esophagus Course: Superior to Posterior Mediastinum
Located behind: Arch of Aorta
Pericardium & Left Atrium
Enters Esophageal Hiatus of the Diaphragm at level of T10
Anatomic Impressions or “Constrictions”:
1. Crossing with Aortic Arch
2. Crossing with Left Main Bronchus
3. Diaphragmatic Hiatus

20. Thoracic Duct Largest lymphatic channel in the body
Originates from Cisterna Chyle in the abdomen & passes thru aortic hiatus of diaphragm at level of T12
Relations: Posterior : bodies of inferior 7 thoracic vertebrae
Anterior : Esophagus
Left : Thoracic Aorta
Right : Azygos Vein
Conveys lymph from:
Lower extremities Left side of thorax
Pelvic Cavity Left side of H & N
Abdominal Cavity Left upper limb

21. Lymph Nodes of the Posterior Mediastinum
Posterior Mediastinal Lymph Nodes
- receives lymph from esophagus, posterior aspect of the pericardium & diaphragm & middle posterior ICS

22. Azygos Venous System of the Posterior Mediastinum
Drains the back & thoracoabdominal walls and the mediastinal viscera
Azygos Vein
- forms a collateral pathway b/w SVC & IVC
- passes to the right side of inferior 8 thoracic vertebrae
- arches over the root of the right lung to enter the SVC
- receives posterior intercostal veins, mediastinal, esophageal & bronchial veins

23. Azygos Venous System of Posterior Mediastinum
Hemiazygos Vein
- arises on left side of the vertebral column to level of T9
- receives the inferior 3 PIV, inferior esophageal veins,
small mediastinal veins
Accessory Hemiazygos Vein
- starts at medial end of 4th or 5th ICS
- descends on left of VC from T5 thru T8
- crosses to the right to join the Azygos Vein
- receives 4th thru 8th IC Veins
- communicates with Superior IC Vein which drains
1st thru 3rd ICS

24. Nerves of Posterior Mediastinum
Thoracic Sympathetic Trunks
- lie against heads of ribs in superior thorax costovertebral joints in midthorax sides of vertebral bodies in lower thorax
Lower Thoracic Splanchnic Nerves
(Greater, Lesser and Least SN)
- presynaptic fibers from 5th thru 12th sympathetic ganglia
- sympathetic innervation for most abdominal viscera

25. References Clinical Anatomy by systems for Richard S. Snell