Superior mediastinum Flashcards
Superior Mediastinum Borders:
- Sup. to transverse thoracic plane
Ant: Manubrium of sternum
Sup: Thoracic inlet
Post: T1 to T4/5
Inferior
• line through sternal angle
• Transverse thoracic plane
• T4/5
Basic arrangement of Superior Mediastinum
anterior to posterior:
Thymus
veins - brachiocephalic and sup. vena cava
arteries - major branches of aortic arch
nerves
hollow structures - trachea and esophagus
Thymus
- Most anterior
- Primary Lymphoid organ
- Located in the inf. part of the neck and the anterior part of the sup.
mediastinum - It can also extend into the anterior mediastinum
- Replaced by fat and connective tissue in adults (after puberty)
Large veins
Great vessels = Right and left Brachiocephalic v
- Formed post. to sternoclavicular joints by the union of the internal
jugular and subclavian veins
- Right Brachiocephalic v.
– Shorter and more vertical
- Left Brachiocephalic v.
– Longer and more oblique
– Anterior to roots of branches of aortic arch
Forms superior vena cava (SVC):
- at the level of the inf. border of the first costal cartilage, the
brachiocephalic vein unites to form the superior vena cava
Superior vena cava
- returns blood from all structures sup. to the diaphragm
(except lungs and heart) - and passes inferiorly and ends at the level of the 3rd costal cartilage
where it enters the right atrium of the heart
Arteries
- Arch of the aorta
- curved continuation of the ascending aorta
- begins post. to the right 2nd sternal costal joint at the level of the
sternal angle
- it arches superiorly, posteriorly, to the left and then inferiorly
- the arch ascends anterior to the right pulmonary artery and the
bifurcation of the trachea
- it reaches its apex at the left of the trachea and esophagus as it
passes over the root of the left lung
- the arch descends post. to the left root of the lung next to the T4
vert.
- the arch ends by becoming the thoracic/ descending aorta
(post. to the left 2nd costal joint)
The arch of the aorta has 3 major branches:
Right:
brachiocephalic trunk
» 1st & Largest
Middle:
L common carotid a.
» Posterior to manubrium
Left: L subclavian a.
» No branches in mediastinum
Nerves of the Sup. med.
vagus - cranial nerve
phrenic - comes from cervical plexus
( C3,4 and 5 keeps the diaphragm alive)
Vagus nerve
- Exits cranium
- descends through the neck, posterio- laterally to the common carotid artery
- each vagus nerve enters the sup. mediastinum posterior to SC joint & brachiocephalic vv.
L &R recurrent laryngeal nn. given off in
sup. mediastinum
- Branches of the L and R vagus nerves
- Right vagus enters thorax ant. to the right subclavian vein - gives rise to right recurrent laryngeal nn
- left vagus descends, post. to the left common carotid, enters the mediastinum in between the left common carotid and left subclavian artery
> as the left vagus nerve curves medially in the inf. border of the arch of the aorta = gives rise to the left recurrent laryngeal nerve
Phrenic nerves
- Right phrenic nerve passes along right side of right brachiocephalic v, SVC and the pericardium over the right atrium
- It also passes anterior to the root of the right lung and descends on the right side of the IVC to the diaphragm which it pierces near the caval opening
> The left phrenic nerve descends between the left subclavian and left common carotid arteries
crosses the left surface of the arch of the aorta ant. to the left vagus n and passes over the left superior intercostal vein
it then descends anterior to the root of the left lung and runs along the fibrous pericardium - superficial to the left atrium and ventricle where it then pierces the diaphragm to the left of the pericardium
