posterior mediastinum Flashcards
what is the anterior boundary of the posterior mediastinum?
posterior pericardium
what is the posterior boundary of the posterior mediastinum?
vertebrae T5-12
what is the lateral boundary of the posterior mediastinum?
mediastinal pleura
what is the superior boundary of the posterior mediastinum?
transverse throacic plane
what is the inferior boundary of the posterior mediastinum?
diaphragm
what is contained in the posterior mediastinum?
- oesophagus
- thoracic aorta
- azygous system of veins
- thoracic duct
- vagus nerve
- sympathetic trunk
- splanchnic nerves
what is the flow of the sympathetic nervous system?
thoracolumbar outflow T1 to L2
what is the flow of the parasympathetic nervous system?
craniosacral outflow - some cranial nerves (including vagus nerve), S2, S3 and S4
what is the sympathetic trunk?
vertical chain of sympathetic nerves running the entire length of the vertebral column
where is the sympathetic trunk located?
both sides of vertebral bodies and the paravertebral ganglia is located along its length
in the thoracic spine how many ganglia are there per spinal level?
one ganglion per spinal level
what happens at spinal nerve levels T1-T4/5?
- preganglionic sympathetic fibres leave the spinal nerve (white rami communicates) and synapse at paravertebral ganglion
- postganglionic sympathetic fibres leave the ganglion (grey rami communicates) and pass to the pulmonary, cardiac and oesophageal plexi
- these nerves can also carry afferent fibres (carrying sensroy information) from the thoracic viscera they supply back to the brain
what is a dermatome?
an area of skin supplied by a single spinal cord level or spinal nerve
where is pain from the heart felt?
down arm and across chest (T1-T4/5)
what nerve supplies to the diaphragm?
phrenic nerve C3, C4 and C5
where can referred pain from the diaphragm be felt?
shoulder
what happens at spinal nerve levels T5/6-T12?
- preganglionic sympathetic fibres leave the spinal cord (white rami communicates) and enter the ganglion but don’t synapse
- hence, preganglionic sympathetic fibres leave these ganglia and synapse in the paravertebral (pre-aortic) ganglia before passing to the abdominal viscera
- there form the 3 splanchnic nerves
where do the greater splanchnic nerves arise from?
levels T5-9
where do the lesser splanchnic nerves arise from?
levels T10-11
where do the least splanchnic nerves arise from?
levels T12
generally where do splanchnic nerves travel?
descend medially from ganglia across the vertebral bodies and enter the abdomen by piercing the diaphragm
what do splanchnic do?
carry preganglionic sympathetic fibres to and visceral afferent fibres from the abdominal viscera
where does the vagus nerve enter?
- enters superior mediastinum posterior to the sternoclavicular joint
- the left and right recurrent laryngeal nerves branch from it but have differing courses
- continues into posterior mediastinum to contribute to pulmonary, cardiac and oesophageal plexues
what type of supply is the vagus nerve?
parasympathetic supply
where does the right vagus nerve travel?
- right recurrent laryngeal branch hooks under right subclavian artery and ascends between trachea and oesophagus
- right vagus continues posterior to the right of the trachea, posterior to right brachiocephalic vein and lung root/hilum
what does the right vagus supply?
the larynx
where does the left vagus nerve travel?
- left recurrent laryngeal nerve hooks inferiorly to the aortic arch, immediately lateral to ligamentum arteriosum
- rest of the left vagus runs posteriorly to lung root
what does the left vagus supply?
the larynx
where does the thoracic aorta travel?
- continues with arch or aorta
- descend on the left side of the vertrbae T5-12
- oesophagus positioned to its right
- terminates at vertebral level T12 where it enters the abdomen through the aortic hiatus in the diaphragm
- thoracic duct and azygous veins ascend on its right hand side and also pass through diaphragm at the aortic hiatus
what are the paired branches of the thoracic aorta?
1) posterior intercostal
2) subcostal
3) bronchial
4) superior phrenic
what are the unpaired branches of the thoracic aorta?
1) pericardial
2) oesophageal
3) mediastinal
where does the azygos vein travel?
- arises on the right side by junction of subcostal (T12) level and ascending lumbar veins
- arches over root of right lung to join SVC
what does the azygos vein do?
- it drains deoxygenated blood from the posterior thoraco-abdominal walls and viscera
- usually receives blood form the Hemiazygous veins which drains the left side
- forms a collateral pathway between the SVC and IVC
what are the tributaries of the azygos vein?
posterior intercostal veins (level T5-T11), bronchial veins, vertebral venous plexus
where does the hemi-azygous vein travel?
- arises on the left side by the junction of subcostal (T12 level) and ascending lumbar veins
- ascends on the left side posterior to aorta draining left posterior intercostal veins level T9-11
- crosses T7/8 to joint azygos and sometimes joins hemi-azygos
what does the hemi-azygos vein do?
- corsses to right and joins azygos vein
- accessory hemi-azygos drains levels T5-T8 on left side
what is the thoracic duct?
the largest lymph channel
what does the thoracic duct do?
conveys all lymph from body except head, neck, upper limb and throat on right side
where does the thoracic duct originate?
Cisterna Chyli in abdomen (L2)
where does the thoracic duct travel?
- ascends through aortic hiatus passing anterior to thoracic vertebrae
- ascends into superior mediastinum and drains into venous system at the left venous angle (junction of internal jugular and subclavian veins)
where does the oesophagus travel?
- descends from superior mediastinum posterior to the trachea
- passes posterior and to the right of aorta
- veers slightly left before piercing through the diaphragm
- becomes anterior to abdominal aorta before entering the stomach
what is the innervation of the oesophagus?
CNX and sympathetic trunk via oesophageal plexus
what is the oesophagus?
a muscular tube
where are the 3 constrictions of the aorta?
1) arch of aorta
2) left main bronchus
3) diaphragm
