Tx Cage Anatomy

Question 1

Which nerves innervate the thoracic wall?

Answer 1

The intercostal and subcostal nerves:

Source: ventral rami of Tx spinal nerves T1-11 (intercostal) and T12 (subcostal)

Course:

• arise from ventral rami of spinal nerves to run between pleura and internal intercostal membrane
• at angle of ribs, enters costal groove between innermost and internal intercostals
• runs length of intercostal space (with intercostal artery and vein) in costal groove

Question 2

What are the branches of the intercostal nerves?

Answer 2

4 branches:

• collateral
• lateral cutaneous
• anterior cutaneous
• muscular

Collateral:

• at angle of ribs
• travels in inferior IC space between innermost and internal IC muscles

Lateral cutaneous: - at mid axillary line

• pierce intercostal muscles
• supply skin over lateral thoracic and abdominal walls

Anterior cutaneous:

• continuation of intercostal nerve anteriorly
• pierce muscles in parasternal line
• supply skin over anterior thoracic wall and chest

Muscular:
- supply all intercostal muscles, subcostals, transverse thoracis, and serratus posterior superior

Question 3

Which two major arteries does the thoracic cage receive blood supply from?

Answer 3

Subclavian
(Anterior Intercostal 1-9)

Thoracic Aorta
(Posterior Intercostal & Subcostal)

Question 4

What are the branches of the subclavian artery in the thoracic cage?

Answer 4

Subclavian 
-
Internal Thoracic
- 
Anterior Intercostal 1-6 (direct branches)

musculophrenic
- Anterior Intercostal 7-9

Question 5

What are the branches of the thoracic aorta in the thoracic cage?

Answer 5

Subcostal & Posterior Intercostal

Posterior Intercostal gives off:

• dorsal
• collateral
• lateral cutaneous

Question 6

What are the 6 arteries of the thoracic cage, and from which major artery did they arise?

Answer 6

Anterior Intercostal
(1-6: subclavian via internal thoracic)
(7-9: subclavian via internal thoracic and musculophrenic)

Posterior Intercostal
(Thoracic Aorta)

Subcostal
(Thoracic Aorta)

Dorsal
(Thoracic Aorta via Posterior intercostal)

Lateral Cutaneous
(Thoracic Aorta via Posterior Intercostal)

Collateral
(Thoracic Aorta via Posterior Intercostal)

Question 7

What is the venous drainage of the thoracic cage?

Answer 7

Venous drainage via:
- posterior & anterior intercostal veins (anastamose and drain into azygos venous system & superior vena cava)

• internal thoracic veins drain into braciocephalic veins, which unite to form superior vena cava)

Question 8

What is the transverse thoracic plane?

Answer 8

Imaginary horizontal line between:

T4/5 & IVD posteriorly

Rib 2 / sternal angle anteriorly

At this level:

• divides superior and inferior mediastinum
• trachea bifurcates
• pulmonary trunk bifurcates
• aortic arch
• azygous vein drains into SVC

Question 9

Describe the mediastinum

Answer 9

Central compartment in the thoracic cavity

Divided into superior and inferior mediastinum at the level of the sternal angle / transverse thoracic plane

Inferior mediastinum further divided into anterior, middle and posterior sections

Mobile compartment to accommodate volume and pressure changes of contents (structures accomodate fluid and air)

Question 10

What are the contents of the mediastinum (overall)?

Answer 10

All thoracic viscera and structures except the lungs:

• heart (middle)
• trachea (superior)
• oesophagus (superior and posterior)
• arch or aorta and branches (superior)
• superior vena cava (superior)
• descending aorta (posterior)
• vagus nerves (superior and posterior)
• phrenic nerves (superior and anterior)
• thymus (superior and anterior)