Posterior Mediastinum and the Neck Flashcards
Where is the carina?
where trachea bifurcates at level of T4/5 vertebrae
Where is the posterior mediastinum?
vertically it runs from the diaphragm to the line that connects the sternal angle with T4/5 junction posteriorly. Section posterior to the heart and pericardium.
What structures are in the posterior mediastinum?
- Descending (thoracic) aorta
- azygos veins
- oesophagus
- thoracic duct
- sympathetic trunk + splanchnic nerves
- posterior intercostal vessels and nerves
What branches does the descending (thoracic) aorta give rise to in the posterior mediastinum?
- posterior intercostal arteries (supply intercostal spaces)
- bronchial arteries (lungs)
- oesophageal branches
- pericardial branches (pericardium)
- phrenic branches (diaphragm)
At what level does the aorta pass through the diaphragm?
T12
Where does the azygos system of veins arise from?
the abdomen at level L1/L2. Goes into posterior mediastinum through diaphragm.
What does azygos system do? (where does it drain blood from)
Drains blood from posterior thoracic wall
Returns it to superior vena cava
Receives blood from…
posterior intercostal veins
Oesophageal veins
Bronchial veins
Describe the position of the oesophagus in the posterior mediastinum
lies right of the aorta
supplied by oesophagal arteries from descending aorta
oesophagal veins return to azygos
passes trhough the oesophageal hiatus in the diaphragm at level T10
What and where is the thoracic duct
Begins at the cisterna chyli and ascends into the thorax, into the neck
Terminates at opening into the venous system at junction of left internal jugular vein and left subclavian vein
Doesn’t drain the right upper limb
Where does the thoracic duct collect lymph from?
Cisterna chyri (collects from lower limbs, pelvis, abdomen)
In thorax, from intercostal spaces and lymph nodes
Left side of head and neck and left upper limb
What drains right side of head and upper limb of lymph?
lymphatic ducts that enter the venous system at the junction of the right subclavian vein and right internal jugular veins
Describe the position of the sympathetic trunk/s
they lie on the posterior thoracic wall
posterior to the parietal pleura
either side of the vertebral column
extends from the skull base to the coccyx
Describe the sympathetic trunks
thin, longitudinal fibre tracks
regularly interspersed with ganglia
sometimes referred to as paravertebral ganglia, as they run parallel to the vertebral column
What is the purpose of the sympathetic trunk?
Allows sympathetic fibres (from T1-L2/3) to reach all parts of the body
How do preganglionic sympathetic fibres enter the sympathetic trunk?
Nerve fibres exit vertebral column at T1-L2/3
Separate from spinal nerves and enter trunk (via connecting branch - white ramus communicans)
In the trunk, it can…
- synapse in the ganglion at entry level
- ascend/descend in trunk before synapsing at a ganglion
- travel through the ganglion and trunk without synapsing
3 things preganglionic sympathetic fibres can do once they enter the sympathetic trunk
- synapse in the ganglion at entry level
- ascend/descend in trunk before synapsing at a ganglion
- travel through the ganglion and trunk without synapsing
When the preganglionic sympathetic fibres synapse with a ganglion in the sympathetic trunk either at entry or after ascending/descending…
…how do the postganglionic axons leave the ganglia?
- enter spinal nerves by connecting branch (grey ramus communications)
- form visceral nerves that convey sympathetic fibres to the head
- form visceral nerves that convey sympathetic fibres to the thoracic viscera
(cardiopulmonary splanchic nerves)
What is white ramus communications?
A short connecting branch allowing preganglionic nerves to enter the sympathetic trunk
What is grey ramus communications?
A short connecting branch that allows postganglionic axons to enter spinal nerves
What are the 4 abdominopelvic splanchnic nerves?
Greater splanchnic nerve (preganglionic fibres originate from T5-T9)
Lesser splanchnic nerve (T10-T11)
Least splanchnic nerve (T12)
Lumbar splanchnic nerve (L1-L2)
Which splanchnic nerves are formed in the posterior mediastinum?
The greater, lesser and least abdominopelvic splanchnic nerves
They traverse the diaphragm to enter abdomen
Ultimately synapse with prevertebral ganglia
What do the posterior intercostal spaces contain?
Intercostal muscles
A posterior intercostal artery (branch of thoracic)
A posterior intercostal vein (drains to azygos system)
A posterior intercostal nerve
What fibres do cardiopulmonary splanchnic nerves convey to thoracic viscera?
Postganglionic sympathetic fibres.
What fibres does the vagus nerve convey to thoracic viscera?
parasympathetic fibres
What are autonomic nerve plexuses?
They look like fine meshes or webs
Can contain parasympathetic and sympathetic fibres
What are the 3 autonomic nerve plexuses in the thorax?
Cardiac plexus
Pulmonary plexus
Oesophageal plexus
What does the cardiac plexus (sympathetic fibres from T1-T5 nerves) innervate?
Sinoatrial node of heart
Sympathetic - increase heart rate and force of contraction
Parasympathetic - decrease “ “
What does the pulmonary plexus innervate?
The bronchi
Sympathetic - relaxes the bronchi
Parasympathetic - constricts the bronchi
What does the oesophageal plexus innervate?
Overlies anterior surface of oesophagus
Sympathetic - inhibit peristalsis
Parasympathetic - stimulate peristalsis
What do visceral afferents do?
Relay sensory information from thoracic viscera back to the CNS via vagus and thoracic splanchnic nerves
What is referred pain? e.g. cardiac referred pain
Pain from one part of the body is felt in another region e.g. cardiac pain felt in central chest, left neck, left arm
How is the heart innervated?
Cardiac plexus (sympathetic fibres from T1-T5 on spine, contains parasympathetic)
Visceral sensory nerves (convey sensory info back to CNS)(enters at T1-T5 alongside sympathetic fibres)
What sensory information is returned to the spinal segments T1-T5?
- visceral sensory information from the heart
- somatic sensory information from skin of chest wall, neck and arm
- this is why brain interprets cardiac pain as pain from chest neck and arm
When does sensation of visceral sensory nerves of the heart reach our conscious perception?
Only when the heart is ischaemic - interpreted as pain, tightness, crushing pressure or burning that may be severe
What is an aortic dissection?
Longitudinal tear in aortic wall
Allows blood to collect between intima and media
Occurs in ascending, arch of, or descending aorta
Presents with sudden onset severe chest pain and/or back pain
What is Horner’s syndrome? (3 signs together)
3 signs:
- small pupil (miosis)
- drooping upper eyelid (ptosis)
- lack of sweating (anhidrosis)
ON ONE SIDE OF TH FACE
Caused by interruption to sympathetic nerves innervating the head
e.g. cancer in apex of lung invading sympathetic chain
What is a hiatus hernia?
When the abdominal segment of the oesophagus and part of the stomach moves proximally through oesophageal opening in diaphragm
Symptoms such as heartburn or reflux
