Regional Anatomy of the Thoracic Cavity

Question 1

Subdivisions of the mediastinum

Answer 1

• Superior mediastinum: located between the superior thoracic aperture and the plane between teh sternal angle and T4/T5 vertebrae (transverse thoracic plane)
• Inferior mediastinum: located between the transverse thoracic plane and the diphragm (inferior thoracic aperture). The inferior mediastinum is further subdivided into:
  
  • Anterior
  • Middle
  • Posterior

Question 2

What is the significance of the transverse thoracic plane?

Answer 2

The transverse thoracic plane is formed by the sternal angle and T4/T5. Its the division between the superior and inferior mediastinum.

The arch of aorta is above the plane and the pulmonary trunk is below. The trachea bifurcates and the azygos vein enters SVC at teh level of this plane.

Question 3

Major structures in superior mediastinum

Answer 3

Thymus, brachiocephalic veins, SVC, arch of aorta and branches, trachea, oeseophagus and many other smaller structures.

Question 4

Thoracic inlet

Answer 4

The thoracic inlet (T1, R1 and manubrium) is transversed by teh trachea, oeseophagus, vesses of upper limba nd head and neck, various nerves, lymphatics, apex of lung and cervical pleura.

It is the continuation between superior mediastinum and root of the neck.

Question 5

Anterior mediastinum

Answer 5

A small amount of CT (fat), sternopericardial ligament and inferior part of thymus.

Question 6

Sternopericardial ligaments

Answer 6

Loosely connects the sternum to the fibrous pericardium.

Question 7

Thymus

Answer 7

Lymphoid tissue, large from birth to puberty. In adulthood mostly replace by adipose tissue. Can be restimulated with autoimmune diseases, endocrine disorders and cancer of the thymus.

Question 8

Middle mediastinum

Answer 8

Fibrous pericardium (fused to central tendon of the diaphragm and tunica adventitia at teh roots of the great vessels), parietal and visceral layers of the seorus pericardium, with paricardial cavity between.

Question 9

Innervation and blood supply of pericardium

Answer 9

The fibrous and parietal layer of serous pericardium is supplied by the phrenic nerves (pain fibres) and pericardiacophrenic artery (from internal thoracic artery).

Question 10

Posterior mediastinum

Answer 10

Oesophagus, descending aorta, azygos system of veins, thoracic duct, vagal trunks, sympathetics.

Question 11

Coninuities between superior mediastinum and posterior mediastinum

Answer 11

Oeseophagus, aorta, numerous arteries, veins, nerves, lymphatics.

Question 12

Location of oeseophagus.

Answer 12

In the superior mediastinum it is located between the rachea and vertebral bodies.

In the posterior mediastinum it is located between the heart and aorta.

Question 13

Arteries in middle mediastinum

Answer 13

Ascending aorta

Question 14

Arteries in superior mediastinum

Answer 14

• Arch of aorta and small branches (e.g. right bronchial a);
• Brachiocephalic trunk (divides into right common carotid and right subclavian arteries)
• Left common carotid artery
• Left subclavian artery

Question 15

Arteries in posterior mediastinum

Answer 15

• Descending (thoracic) aorta
• Most posterior intercostal arteries
• Left bronchial arteries
• Oeseophageal arteries
• Superior phrenic artery

Question 16

Systemic veins

Answer 16

Superior mediastinum: superior vena cava, brachiocephalic veins (R, L) from union of internal jugular vein and subclavian vein.

Posterior mediastinum: azygos system of veins, IVC.

Question 17

Azygos system of veins

Answer 17

Drain posterior intercostal vv and oesophagus and ascending lumbar veins.

Right

Azygos vein and right superior intercostal vein (which joins azygos vein). Supreme intercostal v (or 1st intercostal vein) usually drains into the right brachiocephalic v.

Left

Hemiazygos and accessory hemiazygos veins (to azygos vein) and left superior intercostal veina nd supreme intercostal usually drain to L brachiocephalic vein.

Question 18

Thoracic duct

Answer 18

Enters thorax through aortic hiatus in diaphragm, where it continues from cisterna chyli (chyle cistern). It then ascends between the oeseophagus and vertebral bodies, between aorta and azygos vein (post mediastinum), it terminates in the left brachiocephalic vein or left subclavian vein (sup mediastinum).

Question 19

Phrenic nerves

Answer 19

C3-C5

Motor fibres to diaphragm.

Sensory to pericardium (except visceral), mediastinal pleura, central diaphragmatic pleura and central diaphragmatic peritoneum.

Question 20

Path of the right phrenic nerve

Answer 20

The right phrenic nerve descends along the SVC, passing anterior to the root of the lung, and between mediastinal pleura and fibrous pericardium finally piercing the diaphragm.

Question 21

Path of the left phrenic nerve

Answer 21

The _left _phrenic nerve descends along the arch and ascending aorta passing anterior to the root of the lung, and between mediastinal pleura and fibrous pericardium piercing the diaphragm (thus sensory to the inferior central portion o fthe diaphragm).

Question 22

Vagus nerves and trunk

Answer 22

Parasympathetic to thoracic viscera and many abdominal viscers.

In the neck the vagus is located within the carotid sheath (with common carotid a, internal jugular v). The right vagus travels to right of trachea and the left vagus to left of arch of aorta.

The vagus nn descend posterior to the roots of lung with the left and right vagus splitting to form most of oesophageal plexus, which then reforms as the anteiror and posterior vagal trunks at the lower oesophagus, which enter abdomen with oeseophagus.

Question 23

Recurrent laryngeal nerves

Answer 23

Branches of vagus nerve, the left loops aorund the arch of aorta just posterior to ligamentum arteriosum and the right loops aorund the subclavian artery. They ascend to larynx between trachea and oesophagus.

Question 24

Where are sympathetic preganglionic neuron cell sbodies located?

Answer 24

In T1-L2 lateral horn of spinal cord. Axons exit via the ventral root __> spinal nerve –> white ramus communicans –> sympathetic trunk (paravertebral ganglia).

Some synapse in the trunk with the postganglionic axons re-joining the spinal nerves via gray ramus communcans, or travelling via thoracic cardiac and pulmonary nerves to heart and lungs.

Alternatively preganglionic acons may go through sympathetic ganglia without snaypsing, to form the thoracic splanchnic nerves (greater T5-9(10), lesser T10-11, least T12).

Question 25

Thoracic splanchnic nerves

Answer 25

Sympathetic preganglionic axons which descend to abdominal cavity to prevertebral ganglia (e.g. coeliac ganglion), where they synapse (posthanglionic axons to abdominal viscera).

Question 26

Thoracic splanchnic nerves

Answer 26

Sympathetic preganglionic axons which descend to abdominal cavity to prevertebral ganglia (e.g. coeliac ganglion), where they synapse (postganglionic axons to abdominal viscera).

Question 27

Autonomic plexuses

Answer 27

Mix of parasympathetic and sympathetic and visceral sensory axons.