Posterior Mediastinum Flashcards
Boundaries
Anterior: posterior pericardium Posterior: vertebrae T5-T12 Lateral: mediastinal pleura Superior: transverse thoracic plane Inferior: diaphragm
Contents
Oesophagus, thoracic aorta, azygos system of veins, thoracic duct, vagus nerve, sympathetic trunk, splanchnic nerves
Autonomic Nervous System
sympathetic: thoracolumbar outflow: T1-L2
parasympathetic: craniosacral outflow: some cranial nerves (inc Vagus) & S2, S3, S4
Spinal Nerve Levels T1-T4/5
Preganglionic sympathetic fibres leave spinal nerve (white rami communicantes) and synapse at paravertebral ganglion.
Post ganglionic sympathetic fibres leave ganglion (grey rami communicantes) and pass to pulmonary, cardiac and oesophageal plexi.
These nerves also carry afferent fibres (sensory info) from thoracic viscera they supply, back to brain
Dermatome Map
Pain from heart felt down arms and across chest (T1-4/5).
Sensory supply to diaphragm is partially carried by phrenic nerve - C3, C4, C5.
Referred pain from diaphragm is felt in shoulders.
Spinal Nerve Levels T5/6 - T12
Preganglionic sympathetic fibres leave spinal cord (white rami communicantes) and enter ganglion - but don’t synapse.
Hence, preganglionic sympathetic fibres leave these ganglion and synapse in prevertebral (pre-aortic) ganglia before passing to abdominal viscera - these form 3 splanchnic nerves
Splanchnic Nerves
Greater Splanchnic Nerves: arise from levels T5-T9
Lesser Splanchnic Nerves: arise from levels T10-T11
Least Splanchnic Nerves: arise from level T12
Descend medially from ganglia across the vertebral bodies and enter abdomen by piercing through diaphragm.
Carry preganglionic sympathetic fibres to and visceral afferent fibres from viscera
Vagus Nerve
CNX
Enters superior mediastinum posterior to sternoclavicular joint.
Left and right laryngeal nerves branch from it, but have differing courses.
Continues into posterior mediastinum to contribute to pulmonary, cardiac and oesophageal plexi
Parasympathetic supply
Preganglionic until they reach the plexus
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 the right brachiocephalic vein and lung root and hilum
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
Thoracic Aorta
Continuous with arch of aorta
Descends on the left side of vertebrae T5-T12
Oesophagus positioned to its right
Terminates at T12 where it enters the abdomen through the aortic hiatus in the diaphragm
Thoracic & azygos veins ascend on its RHS and pass through diaphragm at aortic hiatus
Branches of Thoracic Aorta
Paired: posterior intercostal, subcostal, bronchial, superior phrenic
Unpaired: pericardial, oesophageal, mediastinum
Azygos Vein
Arises on right side by junction of subcostal (T12) & ascending lumbar veins
Drains deoxygenated blood from posterior thoraco-abdominal walls and viscera
Tributaries: posterior intercostal veins (T5-11), bronchial veins, vertebral venous plexus
Arches over root of right lung to join SVC
Usually receives blood form hemi azygos vein
Forms a collateral pathway between SVC & IVC
Hemi azygos Vein
Arises on left side by junction of sbcostal (T12) & ascending lumbar vein
Ascends on the left side, posterior to aorta, draining left posterior intercostal veins, levels T9-11
Crosses to right to join Azygos
Accessory hemi-azygos drains T5-8 on left side
Crosses T7/8 to join Azygos and sometimes hemi-azygos
Thoracic Duct
Largest lymph channel
Conveys all lymph from body except head/neck/upper limb and thorax on right side
Originates in cisterna chyli in abdomen (L2)
Ascends through aortic hiatus (anterior to thoracic vertebrae)
Ascends superiorly mediastinum and drains into venous system and eft venous angle (junction of internal jugular and subclavian veins)
