Posterior Mediastinum Flashcards
(16 cards)
Boundaries
Anterior – posterior pericardium Posterior – vertebrae T5-12 Lateral – mediastinal pleura Superior – transverse thoracic plane Inferior -
Contents
Oesophagus Thoracic aorta Azygos system of veins Thoracic duct Vagus nerve Sympathetic trunk Splanchnic nerves
Transcending structures
Oesophagus Thoracic duct Vagus nerve Phrenic nerve Aorta
Thoracic Aorta
Continuous with arch of aorta
Descends on the left side of vertebrae T5-T12
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 azygos veins ascend on its right hand side and also pass through diaphragm at the aortic hiatus
Thoracic aorta branches
Bronchial (paired) Posterior intercostal Subcostal Pericardial Oesophageal Superior Phrenic
Azygous vein
Usually located ascending to the right side of the thoracic vertebra
Drains deoxygenated blood from the posterior thoraco-abdominal walls and viscera
Posterior intercostal veins, bronchial veins, vertebral venous plexus drain into it
Arches over root of right lung to join SVC
Usually receives blood from the Hemiazygos veins which drain the left side
Forms a collateral pathway between the SVC and IVC
Hemi-azygous
Arises on left side by junction of subcostal (T12 level) and ascending lumbar veins
Ascends on the left side posterior to aorta draining left posterior intercostal veins levels T9-11
Crosses to right and joins the Azygos
Accessory hemi-azygos drains levels T4-T8 on left side
Crosses T7/8 to join azygos and sometimes joins hemi-azygos
Thoracic Duct
Largest Lymph channel
Conveys all lymph from body except the head, neck, upper limb and thorax on the right side
Originates in the Cisterna Chyli in abdomen (L2)
Ascends through the Aortic hiatus passing anterior to thoracic vertebrae
Ascends into superior mediastinum and drains into venous system at the left venous angle (junction internal jugular and subclavian junction)
Oesophagus
Descends from Superior mediastinum where positioned posterior to the Trachea
Muscular tube from levels C6-T11
Passes posterior and to the right of aorta
Posterior to the LEFT atrium
Veers slightly left before piercing the Oesophageal hiatus of the diaphragm at level T10
Becomes anterior to abdominal aorta before entering stomach
Three constrictions
Arch of aorta
Left main bronchus
Diaphragm
Innervation: CNX and Sympathetic trunk via Oesophageal plexus
Vagus nerve
Enters superior mediastinum posterior to sterno-clavicular 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 plexi
Parasympathetic supply
Preganglionic fibers until they reach the plexi
Right Vagus
Right recurrent laryngeal branch hooks under right subclavian artery and ascends between trachea and oesophagus
Supplies larynx
Right vagus continues posterior to the right of the trachea, posterior to R. Brachiocephalic vein and lung root
Left Vagus
Left recurrent laryngeal nerve hooks inferiorly to the aortic arch, immediately lateral to ligamentum arteriosum
Ascends similarly to the right nerve to supply the larynx
Rest of left vagus runs posteriorly to lung root
Sympathetic Trunk
Vertical chain of sympathetic nerves running the entire length of the vertebral column
Located on both sides of vertebral bodies
Paravertebral ganglia located along its length
In the thoracic spine usually one ganglion per spinal nerve (intercostal nerve – anterior ramus)
Sympathetic Trunk - Upper 5 ganglia
Preganglionic sympathetic fibers leave the spinal cord (white rami communicantes) and synapse at the ganglion
Postganglionic sympathetic fibers leave the ganlion (grey rami communicantes) and pass to the pulmonary, cardiac oesphageal plexi
Officially these are the Upper Thoracic Splanchnic nerves
These also carry afferent fibers (carrying sensory information) from the thoracic viscera they supply back to the brain
Sympathetic Trunk - Lower 7 ganglia
Preganglionic sympathetic fibers leave the spinal cord (white rami communicantes) and enter the ganglion but don’t synapse
Hence, Preganglionic sympathetic fibers leave these ganglia and pass to the abdominal viscera
These form the 3 (Lower Thoracic) Splanchnic nerves
Lower thoracic splanchnic nerves
Splanchnic refers to viscera
3 Thoracic Splanchnic Nerves:
Greater splanchnic nerves arise from sympathetic trunk and paravertebral ganglia at levels T5-9
Lesser splanchnic nerves arise from levels T10-11
Least splanchnic nerves arise from level T12
Descend medially from ganglia across the vertebral bodies and enter abdomen by piercing the diaphragm (at the crura)
Carry preganglionic sympathetic fibers to and visceral afferent fibers from the abdominal viscera
