mediastinum and imaging : Flashcards
what is the mediastinum ?
Thick midline partition that separates the two pleural cavities.
what are the boundaries of the mediastinum?
superior : superior thoracic aperture inferior :inferior thoracic aperture anterior :manubrium of sternum posterior : thoracic vertebrae
function of the mediastinum?
- allows the passage of structures through from one body region to another - connects thoracic organs to other body regions
recap what is the thoracic inlet?
- consists of the 1st thoracic vertebrae - 1st ribs - manubrium - the great vessels - oesophagus - trachea - nerves - lymphatics
where does the apex of the lung sit?
- 3cm above the clavicle in the neck
where does the right phrenic nerve sit? where does the thoracic duct and azygos vein sit?
- T8 - T12
where is the division of the mediastinum?
- transverse plane between the sternal angle ( CC2) and T4/5
what does the mediastinum split into?
- superior - above sternal angle - inferior - below sternal angle anterior - : anterior to heart in pericardial sac middle - heart in pericardial sac posterior - posterior to pericardial sac and diaphragm
what are the contents of the mediastinum?
- trachea (from C6 to T4) - oesophagus C6 pierces diaphragm at T10 - heart and pericardium - thoracic duct - lymphathic drainage - nerves - great vessels
label a thoracic inlet?
what does the superior mediastinum contain?
- thymus
- great veins
- SVC
- phrenic nerves
- main lymphathic trunks
- vagus nerve
- great arteries
- trachea
- main bronchi
- upper oesophagus
label a superior mediastinum:
what does the posterior mediastinum contain?
- oesophagus
- descending aorta
- thoracic duct
- azygos venous system
- Posterior mediastinal lymph nodes
- Thoracic sympathetic trunks
- Splanchnic nerves
what is the passage of the oesophagus?
- begins at C7 vertebra
- •Enters superior thoracic inlet into superior mediastinum
- enters the posterior mediastinum
- at T7 it deviates to the left and inclines anteriorly so it passes in front of the descending thoracic aorta
- passes through the diaphragm at T10
what are the constrictions of the oesophagus?
- the junction between the pharynx and oesophagus
- where the oesophagus passes the arch of the aorta
- where the oesophagus is compressed by left main bronchus
- at the oesophageal hiatus (the diaphragm)
label the passage of the oesophagus:
what is the superior vena cava made from?
- formed by the asymmetric union of the left and right brachiocephalic veins
- Each brachiocephalic vein – formed by Internal jugular vein + subclavian vein.
what does brachiocephalic actually mean?
brachio - arm
cephalic - head
therefore drains venous blood from brain and arm
label the azygos venous system
refer to netters 3- 15
what is the function of the azygos veins?
- drains the posterior walls of the chest and the upper abdomen
and also the posterior mediastinal organs
what do the hemiazygos veins do?
Accessory hemiazygos (upper) + hemiazygos (lower) veins on left cross thoracic vertebral bodies to join single azygos vein on right
is the azygos symmetrical or asymmetrical?
asymmetrical
what is the thoracic duct?
- the largest lymphatic vessel
- begins on the level of T12
- it enters the thorax through the diaphragm at T12
- At T5, it crosses the midline to the left side and enters the superior mediastinum
what are the great arteries?
Ascending aorta – middle (origin at the left 3rd CC)
Arch of the aorta – superior ( called this from the 2nd CC)
Descending aorta - posterior ( starts at T4)
label the arteries of the thoracic aorta?
refer to netters 3- 14
where is the aorta in regard to the trachea and left main brainchus
- the aortic arch arises anterior to the trachea and arches over the left main bronchus
where does the trachea lie?
the trachea lies behind and between the brachiocephalic and left common carotid artery
where are the phrenic nerves formed?
in the cervical plexus from C3 C4 C5
where does the motor phrenic nerve innervate
where do the sensory phrenic nerves innervate
motor - diaphragm
sensory - central tendon of the diaphragm
mediastinal pleura
pericardium
the peritoneum of the central diaphragm
what surfaces does the right phrenic nerve run on to reach the diaphragm ?
lies on the surface of :
- right brachiocephalic nerve
- superior vena cava
- right side of the heart and the pericardium
what is the general rule of the positioning of the phrenic nerve and the vagus nerve?
phrenic nerve is anterior to the lung root
the vagus nerve is posterior to the lung root
where are the vagus nerves positioned?
where are vagus nerves compared to common carotids?
where does the left vagus nerve pass?
when does the left phrenic nerve pass the vagus?
- vagus nerves are posterior to the lung roots and form plexus following the oesophagus into the abdomen giving branches to heart and lungs on the way
- the vagus nerves are lateral to the common carotids
- the left vagus nerve passes anterior to the aortic arch
- the left phrenic nerve crosses the vagus to cross the aortic arch more anteriorly
where do the left vagus phrenic and vagus nerves sit?
- Cross arch of aorta
- Left phrenic descends in front of lung root
- Left vagus crosses behind root lung gives off left recurrent
how does the laryngeal nerve sit?
- it recurs around the ligamentum arteriosum and the aortic arch
- it then breaks up into many branches around the oesophagus
where does the right vagus nerve lie?
- it lies on the trachea
- it crosses behind the lung root
what happens to the recurrent laryngeal branch?
- it recurs back around the right subclavian artery
- it also breaks up into branches on the oesophagus
what does the vagus nerve provide parasympathetic control to?
control of smooth and cardiac muscle and the glands of gut and airways
where does the vagus nerve act as a sensory nerve?
- the guts and the lungs
what is the recurrent laryngeal nerve?
- it is not parasympathetic
- it runs back up the neck to supply most of the skeletal muscles of the larynx
why is the recurrent laryngeal nerve important?
- it contributes to the muscles allowing us to speak
- in neck surgery if these nerves are damaged then it may cause of voice which is called paralysis
label this diagram
