45 - Mediastinum Flashcards
Mediastinum location
Between left and right pleural cavities.
Divisions of mediastinum
Manubrio-sterno junction/T4/T5 IV disc divides between superior and inferior mediastinum. Middle mediastinum contains heart. Anterior and posterior mediastinum are divided by heart.
Contents of anterior mediastinum
Thymus
*Pictorial representation of mediastinum
Contents of superior mediastinum (anterior to posterior) 1) 2) 3) 4)
1) Thymus 2) Great veins 3) Aortic arch, vagus, phrenic nerves 4) Trachea, oesophagus, thoracic duct, left recurrent laryngeal nerve
Nerves always associated with the aortic arch
Vagus, phrenic nerves
In anterior view, where do veins and arteries of the heart lie?
Veins lie to the right, with the right heart. Arteries lie to the left, with the left heart
Where do the internal jugular veins meet the subclavian veins?
Behind sterno-clavicular joints
Shape of right and left brachiocephalic veins
Right has a more vertical, shorter course. Left has a longer, more horizontal course
Where do the right and left brachiocephalic veins join?
Behind the 1st right costal cartilage
What do the right and left brachiocephalic veins join into?
The SVC
Why is JVP taken preferentially on the right side?
Right brachiocephalic vein has a shorter, more vertical course, into the right internal jugular. This makes it a more accurate indicator of right atrial pressure.
Veins that join to make brachiocephalic vein
Subclavian, internal jugular
Veins that form SVC
Brachiocephalic vein, azygous vein
How does the azygous vein join the SVC?
Arches forward from the posterior thoracic wall, joins SVC behind second costal cartilage
1, 2, 3 of SVC
1) Brachiocephalic veins enter at first costal cartilage 2) Receives azygous vein behind second right costal cartilage 3) Enters heart behind third costal cartilage
Path of the arch of the aorta
Upwards, backwards, to the left. Continues
*Left lateral mediastinum
Part of lungs that aorta arches over
Lung root
What does the ligamentum arteriosum do?
Links the aorta and pulmonary trunk arising from the right ventricle
What do branches of the aortic arch supply?
Head, neck, upper limbs
Fibrous structure that links aorta and pulmonary trunk arising from right ventricle
Ligamentum arteriosum
Branches of aortic arch
1st - Brachiocephalic trunk, which becomes right common carotid and right subclavian 2nd - Left common carotid 3rd - Left subclavian (posterior to 1st and 2nd branches)
Blood vessels that form a ‘V’ around trachea
Brachiocephalic trunk and left common carotid artery
Common alternate arrangement of aortic arch branches
Right common carotid becomes last branch (order of branches becomes rIght subclavian, left common carotid, left subclavian, right common carotid). Right common carotid snakes behind oesophagus( retro-oesophageal). Can make swallowing difficult
Spinal segments innervating diaphragm
C3, C4, C5 keep the diaphragm alive. Innerveate through right and left phrenic nerves.
*Layout of vessels in retroesophageal right common carotid
Path of right phrenic nerve 1) 2) 3) 4) 5)
1) Originates at C3, C4, C5 2) Descends on scalenus anterior 3) Travels between subclavian vein and artery 4) Passes anterior to lung root 5) Pierces diaphragm with IVC, innervates diaphragm.
Part of mediastinum where phrenic nerves are found
Always most lateral structures in mediastinum
*Pictorial representation of phrenic nerve paths
Which structures is right phrenic nerve lateral to?
Venous structures. SVC, right atrium, IVC
Which structures is left phrenic nerve lateral to?
Arterial structures. Aortic arch, left ventricle
What do the phrenic nerves supply with sensory innervation?
Mediastinal and diaphragmatic pleura. Mediastinal and diaphragmatic pericardium.
How do phrenic nerves innervate diaphragm?
Pierce diaphragm with IVC. Provide innervation from abdominal side
Where do phrenic nerve and IVC pierce diaphragm?
T8
Nerve intimately associated with arch of the aorta
Vagus nerve
Where in neck does vagus nerve run?
Postero-lateral to common carotid artery
Neurovascular bundle in mediastinum
Common carotid arteries, internal jugular veins, vagus nerves
Where does the vagus nerve pierce the diaphragm?
At the oesophageal hiatus at T10
Which nerve pierces diaphragm with the IVC?
Phrenic
Which nerve pierces diaphragm with the oesophagus
Vagus
Path of right vagus nerve 1) 2) 3) 4) 5)
1) Originates as a cranial nerve 2) Runs alongside trachea 3) Goes behind lung root 4) Ramifies, forms oesophageal plexus on anterior oesophagus 5) Passes through diaphragm at oesophageal hiatus at T10.
Path of left vagus nerve 1) 2) 3) 4) 5) 6) 7) 8)
1) Originates as a cranial nerve 2) Runs alongside trachea 3) Passes lateral to aortic arch 4) Passes posterior to phrenic nerve 5) Crossed by superior intercostal vein 6) Gives off left recurrent laryngeal nerve 7) Goes behind lung root 8) Runs along anterior oesophagus
Relationship to aorta that phrenic and vagus nerves have
Phrenic are anterior to aorta, vagus are posterior
Where does left recurrent laryngeal nerve branch from?
From left vagus nerve, behind the left lateral side of the arch of the aorta.
Path of left recurrent laryngeal nerve 1) 2) 3)
1) Originates from left vagus nerve, behind left lateral side of arch of aorta. 2) Travels under ligament arteriosum 3) Ascends to larynx through tracheo-oesophageal groove
Where does the right recurrent laryngeal nerve branch from?
From right vagus nerve. Travels under right subclavian artery
Where in mediastinum is trachea?
Superior mediastinum. Lies anterior to oesophagus
Where does oesophagus begin?
C6
Narrowings of oesophagus 1) 2) 3)
1) At beginning (C6) 2) Where is passes arch of aorta (not an intrinsic narrowing. Where aorta impinges on oesophagus) 3) Where it passes through the diaphragm
Path of oesophagus relative to spine
Travels centrally, tilts off to the left before piercing diaphragm
Structure through which lower half of body, upper left quarter of body drains lymph
Thoracic duct
Path of thoracic duct 1) 2) 3)
1) Starts at aortic hiatus at T12 between crura. 2) Runs at back of oesophagus. 3) Arches into the junction between the left internal jugular vein, left subclavian vein.
How does upper right quarter of body drain lymph?
Through right lymphatic channel. Is much smaller than left (thoracic duct)
Path of descending aorta
Left of vertebral column
Branches of descending aorta 1) 2) 3) 4)
1) Intercostal (posterior) 2) Bronchial 3) Pericardial 4) Oesophageal
Structures within the posterior mediastinum 1) 2) 3) 4) 5)
1) Descending aorta 2) Oesophagus, oesophageal plexus 3) Azygous veins 4) Thoracic duct 5) Sympathetic trunk
