Superior and anterior mediastinum

Question 1

Boundaries of the superior mediastinum

Answer 1

Superior: superior thoracic aperture

Inferior: thoracic transverse plane

Laterally: mediastinal pleura

Anteriorly: manubrium

Posteriorly: T1-T4/5

Question 2

Boundaries of the anterior mediastinum

Answer 2

Anteriorly: Sternum

Posteriorly: Pericardial sac

Inferiorly: diaphragm

Laterally: mediastinal pleura

Question 3

Location of the thymus

Answer 3

Most of it is in the superior mediastinum, especially in adults (atrophies with age).

The inferior section is in the anterior mediastinum.

Question 4

Lymphatic drainage by thymus

Answer 4

Following nodes receive lymph from thymus:
Brachiocephalic

Parasternal

Tracheobronchial

Question 5

Arteries in the superior mediastinum

Answer 5

Aortic arch- starts and end on the thoracic transverse plane.
Its branches:
Brachiocephalic trunk

Left subclavian artery

Left common carotid artery

Question 6

Branches of the aorta

Answer 6

Brachiocephalic artery: branches from the aortic arch into the right subclavian artery and right common carotid artery.

Ascending: left subclavian and common carotid artery.

Descending: Branches into the intercostal arteries, lumbar arteries (more inferiorly) and the bronchial arteries.

Question 7

Veins in the superior mediastinum

Answer 7

Moving inferiorly:

L+R internal jugular veins join with L+R subclavian veins to lead into L+R brachiocephalic veins.

The brachiocephalic veins join into the superior vena cava, entering the right atrium.

Summary;
Internal jugular veins
Subclavian veins
Brachiocephalic veins: the left brachiocephalic is longer is it is further away from the right atrium than the right.
Superior vena cava.

Inferior thyroid veins also drain into brachiocephalic veins.

Question 8

Blood supply of the thymus

Answer 8

Supplied by branches of the internal thoracic arteries.

Veins: drain into the brachiocephalic veins

Question 9

Origination of the phrenic nerves.

Answer 9

Anterior rami of: C3-5

Enters the superior mediastinum between the brachiocephalic veins and subclavian arteries.

Enters anterior mediastinum to main bronchus.

Question 10

Phrenic nerve innervation in the superior mediastinum

Answer 10

The only motor supply of the diaphragm, also offers a third supply of sensory fibres.

Question 11

Ligamentum anteriosum

Answer 11

Vestigial ligament that is an embryological remnant of the ductus arteriosus.

Ductus arteriosus was a duct that allowed blood to pass between the arch of aorta and the pulmonary trunk, this allows the blood to bypass lungs in the fetus that are not functioning.

Ductus arteriosus closes at birth, leaving the ligament- ligamentum arteriosum.

Question 12

Vagus nerve in the mediastinum.

Answer 12

Cranial nerves C3-5

Enters the superior mediastinum more medial than the phrenic nerves.

Supplies the larynx via the recurrent laryngeal nerve.

Enters the posterior mediastinum to supply the main bronchi, coursing the bronchi posteriorly.

Provides parasympathetic supply to the cardiac, pulmonary and oesophageal plexi.

Question 13

Thoracic duct

Answer 13

Rises from the posterior mediastinum into the superior mediastinum.

Drains lymph from the left into the venous angle- where left subclavian and left internal jugular vein meet.

Venous angle also receives drainage from these lymphatic trunks;
Jugular
Subclavian
Bronchomediastinal

Question 14

Organs in the anterior mediastinum

Answer 14

Thymus, in children. It atrophies with age.

Pericardial-sternal ligaments: connects pericardium to sternum.

Lymph nodes and vessels.

Internal thoracic arteries.

Question 15

Recurrent laryngeal nerve

Answer 15

Branch from the vagus nerve that supplies the larynx.

Loops up and under the aortic arch before returning to supply the larynx.

Question 16

Trachea

Answer 16

Located in the superior mediastinum.

Structure:
C-shaped hyaline cartilage- allows flexibility and resistance to tension.
Trachealis muscle posteriorly- allows constriction of airway.
Connects larynx to bronchi

Question 17

Oesophagus

Answer 17

Located in the superior mediastinum, runs from pharynx to the stomach.

Essentially just a tube of muscle.