4. Superior mediastinum Flashcards
Location of the mediastinum
Extends from the superior thoracic aperture (inlet) to the inferior thoracic aperture and between the sternum anteriorly and the thoracic vertebrae posteriorly
What is the purpose of the mediastinum?
Acts as a conduit for structures (e.g. nerves, airways, GI tract) that pass through the thorax from one body region to another and for structures that connect thoracic organs to other body regions
What vertebral levels do the IVC, oesophagus and aorta go through the diaphragm?
T8: IVC
T10: Oesophagus
T12: Descending aorta
What are the different divisions of the mediastinum?
Superior (superior thoracic aperture to sternal angle)
Inferior (sternal angle to inferior thoracic aperture)
What are the 3 divisions of the inferior mediastinum?
Anterior: anterior to heart in pericardial sac
Middle: pericardial sac and heart (largest)
Posterior: posterior to pericardial sac and diaphragm
List the (8) contents of the superior mediastinum from anterior to posterior
Thymus Phrenic Nerves Great veins Main lymphatic trunks Vagus nerves Great arteries Trachea and main bronchi Upper oesophagus
Describe the position of the Superior vena cava
Enters right atrium from above
Offset slightly to right of chest
Formed by asymmetric union of right and left brachiocephalic veins
Describe the position of the Inferior vena cava
Enters right atrium from below, through central tendon of diaphragm (at T8)
Majority of IVC is in abdomen (little in thorax)
Which veins join to form the left and right brachiocephalic veins?
Internal jugular veins from head and subclavian veins from upper limbs
Describe the positioning of where the left brachiocephalic vein joins the right brachiocephalic vein
Left brachiocephalic vein crosses posterior to manubrium to join the right brachiocephalic vein to form the SVC.
Joining occurs just off to the right between the sterno-clavicular joint and the joint between the manubrium and 1st rib
Role of the azygous vein
Drains the posterior wall of the thorax (e.g. posterior intercostal muscles) and abdomen
Drains into the superior vena cava
What are the 3 components of the azygous system?
Azygous vein
Accessory hemi-azygous vein
Hemi-azygous vein
What are the branches of the ascending aorta and aortic arch?
Ascending aorta: Right and left coronary arteries Aortic arch: Brachiocephalic trunk: divides into right common carotid and right subclavian arteries Left common carotid artery Left subclavian artery
Describe the relations of the aorta and great arteries to the airway
Aortic arch arises anterior to trachea
Arches over the left main bronchus at the lung root
Trachea lies behind and between brachiocephalic and left common carotid arteries
Oesophagus lies behind trachea
What and where do common carotid arteries divide into?
Divide into external and internal carotids high in the neck
Where is the pulmonary trunk and what is its function?
Emerges from right ventricle
Carries deoxygenated blood to lungs
Divides into left and right pulmonary arteries
What connects the pulmonary trunk to the aortic arch? What is this a remnant of?
Ligamentum arteriosum connects PT to aortic arch.
Remnant of the ductus arteriosus (blood bypasses lungs in foetal life)
Describe the ductus arteriosus
At junction between pulmonary trunk and aorta
Any blood on way to lungs in foetus can get diverted through the ductus arteriosus which connects straight back to aorta
After birth, ductus arteriosus closes to form ligamentum arteriosum
Where are phrenic nerves formed?
Formed in the cervical plexus from C3, 4, 5
“C3,4,5 keeps the diaphragm alive”
What are the phrenic nerves motor to?
Diaphragm
What are the phrenic nerves sensory to?
Central tendon of the diaphragm
Mediastinal pleura
Pericardium
Peritoneum of central diaphragm
The right phrenic nerve reaches the diaphragm lying on the surfaces of…
Right brachiocephalic vein
Superior vena cava
Right side of heart and pericardium (in front of lung root)
Describe the relations of great arteries to main nerves
Vagus nerves lateral to common carotids
Left vagus passes anterior to aortic arch
Left phrenic crosses vagus to cross aortic arch more anteriorly
Describe the relations of lung roots to main nerves
Vagus nerves go behind lung roots
Phrenic nerves go infront of lung roots
Describe the positioning of left phrenic and vagus nerves
Cross arch of aorta
Left phrenic descends in front of lung root
Left vagus crosses behind lung root, gives off left recurrent laryngeal nerve: recurs around ligamentum arteriosum and aortic arch
Left vagus breaks up into many branches round oesophagus (so also passes through diaphragm at T10)
Describe the positioning of the right vagus nerve
Lies on the trachea
Crosses behind the root lung
Recurrent laryngeal branch: recurs around right subclavian artery
Breaks up into branches on oesophagus
