8. Posterior Mediastinum Flashcards
What are the different divisions of the mediastinum?
Superior (above sternal angle)
Inferior (below the sternal angle)
Inferior is divided into anterior, middle and posterior
Describe the arrangement of the vagus nerve and phrenic nerve in the mediastinum.
Vagus nerve runs posterior to the airways
Phrenic runs anterior to the airways and is embedded in the pericardium
What do the left and right recurrent laryngeal nerves wind around?
Left: Aorta
Right: Right subclavian artery
Contents of posterior mediastinum
Oesophagus Descending aorta Thoracic duct Azygos venous system Posterior mediastinal lymph nodes Thoracic sympathetic trunks Splanchnic nerves
Where does the oesophagus begin and end?
Pharynx to stomach
Begins C7
Ends T11
Where does the oesophagus pass through the diaphragm?
T10
Describe the position of the oesophagus above and below T7
Above T7: Right of aorta
Below T7: Left of aorta
Where are the 4 constrictions of the oesophagus?
Junction of oesophagus with pharynx
Where oesophagus is crossed by arch of aorta
Where oesophagus is compressed by left main bronchus
At the oesophageal hiatus (where oesophagus passes through diaphragm to abdominal cavity)
Describe the position and orientation of the azygous vein.
Runs along the right side of the vertebral bodies and arches anteriorly over the right main bronchus to join the SVC.
Arteries to the oesophagus
Branch of the aorta directly as adjacent to oesophagus
Intercostal arteries
Posterior: Emerge from aorta
Anterior: Emerge from thoracic vessels
What differs about the posterior blood supply to intercostal spaces 1 and 2? Why?
Aorta doesn’t extend that high
Posterior intercostal going to spaces 1 and 2 receive their supply from above (left and right subclavian arteries- which give rise to supreme intercostal artery)
Describe the azygos venous system.
Azygos vein runs along the right side of the vertebral bodies and drains the right side of the chest wall. Accessory hemiazygos (superior to the hemiazygos) and the hemiazygos drain the left side of the chest wall and drain into the azygos.
Azygos then arches anteriorly over the lung root and joins the SVC just above right atrium
What is the purpose of the azygous venous system
Drains posterior wall of chest, upper abdomen and posterior mediastinal organs
Describe the relations of the azygos vein.
Azygos vein arches anteriorly over right lung root to join the superior vena cava.
Describe the arrangement of the vagus nerve and phrenic nerve in the inferior mediastinum.
Vagus nerve runs posterior to the airways and forms plexus following oesophagus into abdomen
Phrenic runs anterior to the airways and crosses pericardium to diaphragm
What are the main branches of the vagus nerve?
Parasympathetic: to heart and lungs (control of smooth and cardiac muscle + glands of gut and airways)
Large sensory fibres from gut and lungs
Recurrent laryngeal nerve (voluntary) is NOT parasympathetic: it runs up the neck to supply most skeletal muscles of the larynx
What structure does the right vagus nerve lie on?
Trachea
Describe the relations of the vagus nerves to the great arteries.
Run lateral to the 2 common carotid arteries.
Describe the paths of the left vagus and left phrenic nerves.
Left vagus crosses anteriorly to the aortic arch and behind lung root
Left phrenic nerve crosses more anteriorly in front of the aortic arch.
What structures do the phrenic nerves provide sensory and motor innervation to?
Motor: diaphragm Sensory: central tendon of diaphragm mediastinal pleura pericardium peritoneum of central diaphragm
What vertebral level do the phrenic nerves emerge from?
C3, 4 and 5
Where does the vagus nerve go through the diaphragm?
T10
What is the nerve that branches off the vagus in the mediastinum near the left lung?
Left recurrent laryngeal nerve
Describe the path of the right phrenic nerve to reach the diaphragm.
Right phrenic nerve passes along the right brachiocephalic vein, along the SVC, and along the right side of the heart and pericardium to the diaphragm.
Describe the path of the left recurrent laryngeal nerve.
The left recurrent laryngeal nerve is a branch of the left vagus nerve, which arches around the ligamentum arteriosum and moves up towards the larynx.
Describe the path of the right recurrent laryngeal nerve.
The right recurrent laryngeal nerve branches off the right vagus nerve more superiorly and loops around the right subclavian artery.
Which positions do the right and left vagus nerves occupy?
Left: Occupies position on front, becomes Anterior vagal trunk
Right: Occupies position on back, becomes Posterior vagal trunk
Which spinal nerves do the sympathetic trunk receive branches from?
T1-L2
What is the role of sympathetic trunks?
Distribute sympathetic nerves to smooth muscle and glands throughout body
Where do the nerves to the body wall synapse?
In ganglia of sympathetic trunks
Where do the nerves to the internal organs synapse?
In local ganglia
What do sympathetic trunks bring?
Pain fibres back to CNS from viscera
What are the fibres in the lower sympathetic trunk called and which vertebral levels do they branch off at?
Splanchnic Nerves
T5-T12
What vertebral levels do the IVC, oesophagus and aorta go through the diaphragm?
8, 10, 12
