Superior Mediastinum Flashcards
What separates the superior and inferior mediastinum?
Imaginary line running from sternal angle to T4 vertebrae
What is the mediastinum
Central compartment of thoracic cavity, located between the pleural sacs, acts as conduit for transverse structures from thorax to abdomen
Sternal angle
Angle formed by junction of sternal body and manubrium
Superior mediastinum
Extends upwards, terminates at superior thoracic aperture
Inferior mediastinum
Extends downwards, terminates at diaphragm. Subdivided into anterior mediastinum, middle mediastinum and posterior mediastinum
Borders of the superior mediastinum
Superior - thoracic inlet
Inferior - continuous with inferior mediastinum at level of the sternal angle
Anterior - manubrium of the sternum
Posterior - vertebral bodies of T1-4
Lateral - pleurae of the lungs
3 major branches of aortic arch arise within
Superior mediastinum
Brachiocephalic artery
Supplies right side of the head and neck and right upper limb
Left common carotid artery
To the left side of the head and neck
Left subclavian artery
To the left upper limb
Brachiocephalic veins (superior vena cava)
Drain blood from the upper body
Left superior intercostal vein (superior vena cava)
Collects blood from the left 2nd and 3rd intercostal vein. It drains into left Brachiocephalic vein
Supreme intercostal vein
Drains the vein from first intercostal space directly into the Brachiocephalic veins
Azygous vein
Receives blood from right posterior intercostal veins. The left intercostal veins drain first into the hemiazygos and accessory hemiazygos veins before joining the azygos vein around T7-T9
Nerves in superior mediastinum
Right vagus nerve, left vagus nerve, phrenic nerve, cardiac nerves, sympathetic trunk
Right vagus nerve
Runs parallel to the trachea and passes posteriorly to the superior vena cava and right primary bronchus
Left vagus nerve
Enters superior mediastinum between the left common carotid and the left subclavian arteries. It descends anteriorly to the aortic arch, before travelling posterior to the left bronchus
Left recurrent laryngeal nerve
Arises from left vagus nerve as it passes the aortic arch. Loops under the arch to the left ligamentum arteriosum before continuing to the larynx in the tracheal-oesophageal groove
Phrenic nerve
From anterior surface of anterior scalene muscle, phrenic nerves (roots C3,C4,C5) enter the superior mediastinum lateral to the great vessels. They then descend anteriorly into the middle mediastinum and pass anteriorly to the hilum of the lungs
Cardiac nerves
Originate from superior, middle, inferior cardiac ganglion and form the superficial and deep cardiac plexuses in superior mediastinum. The superior plexus sits between the aortic arch and right pulmonary artery. The deep plexus lies on the surface of the trachea at the point of bifurcation.
Sympathetic trunk
Runs bilaterally to the vertebral bodies along the entire length of the vertebral column
Other structures in superior mediastinum
Thymus, trachea, oesophagus, thoracic duct, muscles
Thymus (superior mediastinum)
Most anterior structure. Sits against posterior surface of sternum and extends into anterior mediastinum, can reach into the neck
Trachea (superior mediastinum)
Trachea bifurcates into primary bronchi posterior to ascending aorta at level of sternal angle
Oesophagus (superior mediastinum)
Ascends towards pharynx, joins at the level of C6
Thoracic duct (superior mediastinum)
Thoracic duct passes to the left of oesophagus to the junction of the left internal jugular and subclavian veins
Muscles (superior mediastinum)
Sternohyoid and sternothyroid muscles originate from posterior surface of the manubrium (part of the infrahyoid muscle group of neck)
Inferior aspect of longus colli muscle originates within superior mediastinum
