Part 4: Superior Mediastinum Flashcards
Describe the general asymmetry of the superior mediastinum
Veins are on right and arteries on left
What are the boundaries of the superior mediastinum
Anterior: Manubrium
Posterior: T1-4
Which structures occupy the midline of thoracic inlet?
Trachea and oesphagus
Describe the aortic arch
Arises from LV. Arch passes from front to back with concavity at level of 2nd CCJ over L bronchus and pulmonary trunk bifurcation. At apex gives off brachiocephalic trunk, then L common carotid and L subclavian just behind L SC joint.
Where does ligamentum arteriosum join?
Remains of ductus arteriosus. Attaches from L pulmonary trunk to aortic arch just after L SC artery.
What physiologic receptors are in the aortic arch?
Baroreceptors - in adventitial layer, contribute to heart rate
Aortic bodies - like carotid bodies help detect hypoxia important with respiratory reflexes
Describe the formation of the SVC
Brachiocephalic veins arm formed just behind SC joints bilaterally from IJV and SCV. The IJV lies lateral to CCA in front of scalenus anterior. R BCV runs downward while L BCV runs almost horizontal. The 2 merge to form SVC at 1st R costal cartilage
What veins other than brachiocephalic drain into SVC?
vertebral, internal thoracic, inferior thyroid plexus, left superior intercostal and large thymic join at commencement.
Azygous joins at 2nd costal cartilage.
Describe course of SVC
Begins at 1st costal cartilage - border of sternum
Pierced by azygous vein 2nd costal cartilage
Enters upper border of RA at 3rd costal cartilage
Where does the thoracic duct empty?
At commencement of SVC
The cardiac plexus consists of deep and superficial parts. What contributes to superficial part?
Union of L vagus and L cervical sympathetic ganglion
What forms deep part of cardiac plexus?
Fibres from L+R vagus, recurrent laryngeal, cervical and sympathetic ganglion
Where does the trachea commence superiorly?
C6 - continuation of larynx
What are the anterior and posterior relationships of the trachea?
Anterior: Manubrium with sternohyoid and sternothyroid on each side. Brachiocephalic trunk and L CCA diverge each side
Posteriorly: Oesphagus
What are the left and right relationships of the trachea?
Right: Right brachiocephalic and SVC, vagus nerve and arch of azygous
Left: L CCA, L SCV, aortic arch, left recurrent laryngeal nerve
Where does the pulmonary trunk lie in relation to the trachea?
Left of tracheal bifurcation, in front of L bronchus
What is the blood supply to the trachea?
Inferior thyroid arteries and bronchial arteries - venous drainage to inferior thyroid plexus
What is the structure of the trachea?
15-20 C-shaped cartilages, bound by transverse muscles posteriorly. Has pseudostratified columnar epithelium with goblet cells and mucous glands
Describe the course of the phrenic nerve
Passes down middle mediastinum but trys to get as lateral as possible.
R phrenic sits between pleura and R BCV, SVC, RA, IVC and passes through central tendon with IVC
L phrenic lies between pleura and L CCA, L SCA, crosses aortic arh lateral to superior intercostal vein, over LV to apex and pierces diaphragm though muscle.
Both give off anterior, lateral and posterior branches to diaphragm from underside
What vessel supplies the phrenic nerve?
Pericardiocophrenic artery (branch of internal thoracic)
What nerve roots is phrenic artery?
C3,4,5 - mainly C4
Describe the course of the vagus nerve
Runs in middle mediastinum and tries to get to midline.
R Vagus - in contact with trachea
L Vagus - held off trachea by great arteries, crosses arch medial to superior intercostal vein
Each passes down behind lung root with supply to pulmonary plexus then reach midline by forming oesphageal plexus
Where does the recurrent laryngneal nerve arise?
R RLN - arises from vagus at root of neck and hooks around R SCA
L RLN - arises from vagus as it passes over arch of aorta. Hooks around ligamentum arteriosum.
What do the recurrent laryngeal nerves supply?
Whole trachea
Adjacent oesophagus
Most importantly supply muscles of larynx
