Mediastinum: Superior, Anterior and Posterior Flashcards
What is the mediastinum?
- central compartment of the thoracic cavity
- surrounded by loose connective tissue
What is the superior limit of the superior thoracic aperture, also called the thoracic inlet?
- manubrium
- 1st rib
- clavicle
- T1-T4 vertebrae
What is the name given to the plane that lines the inferior border of the superior mediastinum, separating it from the inferior mediastinum?
- transverse thoracic plane
- also known as plane of ludwig
What is the anatomic position of the transverse thoracic plane?
- sternal angle / angle of Louis
- T4-T5 vertebrae
What is the importance of the transverse thoracic plane/plane of ludwig?
- important structures are formed or divide here
- arch of aorta
- bifurcation of trachea at carina
What are the 2 principle nerves that pass through the superior mediastinum?
- vagus nerve
- phrenic nerve
Which vertebrae does the phrenic nerves originate from?
- C3, 4 and 5
- keeps us alive
What are the great vessels that pass through the superior mediastinum?
- arteries = arch of aorta and branches
- veins = brachiocephalic veins and superior vena cava
What are the visceral structures that pass through the superior mediastinum?
- thymus gland (part)
- trachea
- oesophagus
- thoracic duct
The brachiocephalic veins pass anteriorly to the aortic arch, which in turn is in front of what visceral structure?
- trachea
What is the first vein that the superior vena cave bifurcates into in the superior mediastinum?
- the left and right brachiocephalic veins
Is the left or right brachiocephalic vein longer?
- left
- crosses over superior aspect of aortic arch
What do the left and right brachiocephalic veins bifurcate into?
- internal jugular veins (left and right)
- subclavian veins (left and right)
Why would a catheter that needs to enter the heart be better places in the right jugular vein and the left jugular vein?
- more direct route
What does ABCs stand for when looking at the arteries of the superior mediastinum?
- A = aorta
- B = brachiocephalic
- C = common carotid arteries
- S = subclavian arteries
Is there a left and right brachiocephalic artery?
- no just the right
What does the brachiocephalic artery bifurcate into?
- right common carotid artery
- right subclavian artery
Where do the left subclavian and common carotid arteries bifurcate directly from?
- aortic arch
A fracture to the 1st rib is uncommon, but if it occurs it has a mortality of 30%, why is this so high?
- subclavian artery and vein runs between 1st rib and clavicle
- damage to rib likely damages blood vessels
- ⬆️ risk of haemorrhage
In addition to damaging the subclavian artery ands vein, a fracture of the 1st rib can cause damage to a nerve, which nerve is this?
- brachial plexus
What is the ligamentous arteriosum?
- fibrous connective tissue
- connects aortic arch and pulmonary artery
What did the ligamentous arteriosum originate from?
- ductus arteriosus
What is the ductus arteriosus?
- known as a shunt
- blood vessel connecting aortic arch and pulmonary artery
- important prenatally as lungs dont function
What is the foramen ( in the heart called fossa ovalis), and where is it in the heart?
- opening
- in heart known as a shunt
- hole connecting left and right atria in babies
- blood misses the lungs which are not formed yet
When do the foreman and ductus arteriosus close?
- at birth
Do the the phrenic nerves supplying the diaphragm and pericardium provide sensory infromation (pain, stretch etc..)?
- yes
Where do the phrenic nerves enter the superior mediastinum?
- between brachiocephalic veins and subclavian arteries
- anterior to the trachea
Where do the vagus nerves originate from?
- 10th cranial nerve in brainstem
Where do the vagus nerves enter the superior mediastinum?
- medially compared to phrenic nerves
- runs close to trachea on the right - on left aorta keeps away from trachea
Where is the thymus gland located?
- posterior to sternum
- crosses superior and anterior mediastinum
What does parasternal mean?
- vertical line on front of thorax
- either side of the sternum
Which lymph nodes drain into the thymus gland before it becomes fibrotic?
- parasternal, brachiocephalic and tracheobronchial
What supplies the blood to the thymus gland?
- internal thoracic arteries
When does the thymus gland atrophy and become fibrotic?
- after puberty
What is the neuromuscular disease that has been linked with a benign growth of the thymus gland?
- myasthenia gravis
From the vertebrae, is the oesophagus or trachea closer to the anterior aspect of the body?
- trachea - oesophagus lies on the vertebrae
What is the oesophagus generally composed of?
- muscular tube
The oesophagus generally runs medially, however it is pushed to the left because of what?
- aorta
What is the thoracic duct?
- largest lymphatic channel - transports lymph to venous system
Where does the thoracic duct drain into the venous system?
- aprox T4 vertebrae
- into internal jugular and subclavian veins
What are the borders of the posterior mediastinum?
- anterior = pericardium
- posterior = T2-T12
- lateral = mediastinal pleura (lungs)
- superior = transverse thoracic plane
- inferior = diaphragm
What are the 2 main vessels of the posterior mediastinum?
1 - thoracic aorta 2 - azygos system of veins
What are the 3 main nerves running through the posterior mediastinum?
1 - vagus nerve 2 - sympathetic trunk 3 - splanchnic nerves
What are the 2 main visceral structures running through the posterior mediastinum?
1 - oesophagus 2 - thoracic duct
Where does the thoracic aorta lie in the posterior mediastinum?
- left side of T5-T12 vertebrae - oesophagus, thoracic duct and azygos veins lies to the right
What are the 2 anatomical landmarks to identify where the thoracic aorta ends in posterior mediastinum?
- vertebrae T12
- hiatus (hole) of diaphragm
There are 9 pairs of posterior intercostals vessels, where do they run in the intercostals?
- along groove on inferior aspect of ribs
The most superior pair of intercostal vessels are not supplied by the thoracic aorta, where do they come from?
- subclavian arteries
In addition to the 9 pairs of posterior intercostals vessels supply, what other arteries run off the thoracic aorta?
- subcostal arteries
- pericardium
- pairs of bronchial arteries
- oesophageal
- superior phrenic
If a patient need a pleural drain or sample, is it better to go above or below the ribs?
- above to avoid blood vessels
What are the 2 main components of the venous blood flow in the posterior mediastinum?
1 - azygos veins
2 - hemiazygos veins
Where does the azygos vein drain into?
- superior vena cava
Where does the azygos vein lie?
- right side of thoracic vertebrae
What drains into the azygos vein?
- posterior intercostals
- bronchial veins
- vertebral venous plexus
What 2 components make up the hemiazygos located on the left side of the thoracic vertebrae?
1 - main hemiazygos (T9-T11)
2 - accessory hemiazygos (T5-T8)
The main hemiazygos is from T9-T11, where does it then drain into?
- azygos vein
The accessory hemiazygos drains from superior intercostals. What 2 places is it able to drain into?
1 - directly into azygos vein
2 - main hemiazygos and then into azygos vein
What is the structural importance of having the azygos on the right hand size of the vertebrae?
- if inferior vena cava is damaged azygos can compensate
- colateral blood vessels form
- ⬆️ diameter of azygos
Does the vagus nerve supply parasympathetic or sympathetic stimulus?
- parasympathetic
Where do the right and left vagus nerves originate from in the brain?
- medulla
Where do the right and left vagus nerves enter the mediastinum?
- posterior to sternoclavicular joint
- through superior mediastinum
Where do the vagus nerves try to stay close to?
- midline of the body
Although the right vagus nerves stays relatively central, the left vagus nerve is pushed to the left by what?
- aorta
Where does the right recurrent laryngeal nerve run?
- under right subclavian artery
- between trachea and oesophagus
Where does the right recurrent laryngeal nerve supply?
- larynx
Where does the left recurrent laryngeal nerve run?
- hooks inferiorly to aortic arch
- immediately lateral to ligamentum arteriosum
Where does the left recurrent laryngeal nerve descend after the aortic arch?
- in groove between oesophagus and trachea
When having surgery to the posterior mediastinum what could cause damage to the vocal cords?
- damage to the left recurrent laryngeal nerve
- can cause paralysis of larynx, impairing ability to cough
In addition to surgery what else may impinge on the left recurrent laryngeal nerve causing a horse voice?
- inflamed lymph nodes of the large bronchi
- they would press on the nerve
What is the sympathetic trunk?
- paired bundles of fibres either side of the vertebrae
- form ganglia
The upper 5 functional elements of the sympathetic trunk in the posterior mediastinum pass to which 3 plexus?
1 - pulmonary
2 - cardiac
3 - oesophageal
The upper 5 functional elements of the sympathetic trunk in the posterior mediastinum form what?
- pre ganglionic fibres that then synapse
The lower 5 functional elements of the sympathetic trunk in the posterior mediastinum do not synapse, but instead form pre ganglionic fibres where?
- abdomen
Where does the thoracic duct originate from?
- cisterna chyli (L2)
What is the cisterna chyli?
- a dilated sac
- drains all lymphatics of small intestines
Where does the thoracic ducts ascend?
- through aortic hiatus (hole in diaphragm)
- anterior to thoracic vertebrae
