Anatomy of The Mediastinum Flashcards
1. Identify the divisions of the mediastinum 2. Describe the organisation of the structures in the superior mediastinum 3. Describe the arrangement of the pericardium 4. Describe the contents of the posterior mediastinum 5. Explain the arterial supply and the venous drainage of the thoracic wall 6. Distinguish between the pulmonary and the systemic blood supply to the lungs
Where does the mediastinum start
- Thoracic inlet/aperture
- T1
Where does the mediastinum end
- Diaphragm - end point (inferior boundary)
- the diaphragm can move a bit as it moves up and down
Where is the front and back of the mediastinum
- Thoracic vertebrae - this is the back
- Sternum and costal cartilages - this is the front
the mediastinum is…
Highly mobile because it contains hollow air or fluid filled structures
why does the mediastinum need to be highly mobile
- allows for movement of lungs, heart, great vessels and oesophagus
What divides the heart into superior and inferior
Transthoracic plane
What does the transthoracic plane do
divide the heart into superior and inferior
where is the transthoracic plane
- sternal angle T4/T5
- this is where rib 2 inserts
Define the transthoracic plane
- Transthoracic plane is defined in terms bony body wall structures which are independent of gravity
when you are describing the position of structures what way is the person postioned
Supine
describe where the - arch of the aorta - bifurcation of the trachea - central tendon are in a person in the supine position
- Arch of aorta lies superior to transthoracic plane
- Bifurcation of trachea transected by transthoracic plane
- Central tendon lies at level of xiphisternal junction and T9
describe where the - arch of the aorta - bifurcation of the trachea - central tendon are in a person in a standing position
- Arch of aorta transected by transverse thoracic plane
- Tracheal bifurcation lies inferior to transthoracic plane
- Central tendon falls to middle of xiphoid process T9-10 IV disc
what are the structures in the superior mediastinum
- Brachiocephalic veins and superior Vena Cava
- Great vessels – ascending and arch of aorta
- Trachea
- Oesophagus
- Thymus Gland – overlies the great vessels, in adults it is not as prominent
- Phrenic nerve
- Thoracic duct and lymphatic trunks
What are the structures in the inferior mediastinum
- Heart
- Oesophagus
- Descending aorta
- Inferior Vena Cava
List the structures in the superior mediastinum as if going from anterior to posterior
- Thymus
- Veins
- Brachiocephalic and SVC
- Phrenic nerve
- C3,4,5 – innervation to diaphragm
- Arteries
- Arch of aorta and great vessels
- Vagus nerve and recurrent laryngeal nerves (this is a branch of the veagus nerve)
- Trachea
- Oesophagus
- Thoracic duct and lymphatic trunks
what nerves are in the mediastinum
Vagus
Phrenic
sympathetic trunk
What does the vagus nerve innervate in the mediastinum
- Oesophagus
- Heart
- Bronchi
What does the recurrent Laryngeal loop do
it innervates the larynx
part of the vagus nerve
describe the difference between the left and the right recurrent laryngeal
- On the right side it loops underneath the right subclavian arteries and goes back towards the neck (higher up)
- On the left side it gets stuck underneath and aorta arch before it loops back to the larynx (lower down)
what does the Phrenic nerve innervate
Diaphragm
- sensory to the pericardium mediastinal pleura
what are the spinal levels of the Phrenic Nerve
C3 C4 C5
what are the two phrenic nerves
Left and Right
describe the structure of trachea
- cartilaginous rings U shaped - this keeps it open so it doesn’t collapse and keeps it open with the oesophagus expands behind it
- aortic arch is over the left bronchus and lung root
- bifurcation into the 2 main bronchi happens at the transthoracic plane T4/T5
where does bifurcation of the trachea happen
- bifurcation into the 2 main bronchi happens at the transthoracic plane T4/T5
what spinal level is the trachea from and till
C6-T4
describe the structure of the oespohagus
- posterior to the trachea
- towards the left side but is compressed by the arctic arch at T4 and the root of the left lung
what are the spinal level is the oesophagus from and till
C6-T10
name the spinal levels of
- Neck, end of larynx and pharynx
- thoracic inlet
- transthoracic plane
- diaphragm
- C6
- T1/T2
- T4/T5
- T10
what is the superior mediastinum divided into
- Anterior
- Middle
- Posterior
What is in the Anterior inferior mediastinum
Thymus
What is in the middle inferior mediastinum
- Pericardium and Heart
What is in the posterior inferior mediastinum
- Primary Bronchi
- Oseophagus (and Oesophageal plexus)
- Descending aorta
- Thoracic duct
- Azygos and hemi azygos veins
Describe the structure of the heart
- tough other fibrous pericardium
- serous pericardium - parietal and visceral (fluid between these two layers)
What does the tough outer fibrous pericardium do?
• Prevents over-dilation – stops too much blood going into the heart • Limits the expansion of the heart - stabilises the heart - holds heart in place - protective layer
What does the serous pericardium do
• Leaves potential space between layers of serous pericardium
- allows contraction and expansion due to fluid between the layers
What is another word for the visceral serous pericardium
Epicardium
What is the fibrous pericardium attached to
- Attached to great vessels (aorta, pulmonary artery & veins)
- Attached to diaphragm
what is the partial and visceral layer attached to
- parietal - attached to fibrous layer
- visceral - attached to surface of the heart
What is pericardial effusion
- Happens when you bleed into the pericardial space and therefore there is a build up of fluid
What happens to the fibrous pericardium when pericardial effusion happens
- Normally restricts overexpansion
- But if fluid gathers between parietal and visceral pericardium the heart has no where to go
- Cannot contract and expand as much as it usually does, this can shut down the right ventricle and lead to cardiac tamponade,
where does the heart sit
- Mainly sits behind the sternum and slightly to the left
Describe the outline of the heart
- Superior border - inferior border of 2nd left costal cartilage to superior border of 3rd right costal cartilage
- Right border - 3rd right costal cartilage to 6th right costal cartilage
- Left border - line between left inferior and superior border
- inferior border - inferior end of right border to the 5th intercostal space, Cole to the left mid clavicular line
What does the azygous vein do
- Venus drainage of the thoracic cavity
What is the arterial supply to the posterior thoracic wall
- posterior intercostal arteries - these are branches of the descending aorta this happens from T3-T12 (inferior intercostal arteries)
- From T1-T2 the blood supply is from the costocervical trunk which is a branch of the subclavian artery (superior intercostal arteries)
What is the arterial supply to the chest wall
- ## Intercostal arteries - these run in the upper part of each intercostal space when their nerve and veins in neuromuscular bundles in the costal groove
Describe anterior intercostal arteries
- they originate from the internal thoracic artery which is deep to costal cartilages
- anterior intercostal arteries join with the posterior intercostal arteries in each space
What is the neurovascular bundle protected by
- protected by the inferior part of the rib and is tucked away
What is the neurovascular bundle
- intercostal vein artery and nerve
What is the treatment for pleural effusion
- chest drain mid axillary line normally 5th intercostal space (safe zone) for treating a pneumothorax
- Needle decompression for pneumothorax 2nd or 3rd intercostal space midclavicular line
- thoracentesis
What is a thoracocentisis
- it is sampling or removal of excess of fluid round the lungs
how do you avoid damage when during a thoracentesis
- insert need to the superior of the rib to avoid damage to the intercostal nerve and vessels
- also high enough to avoid the collateral vessels
- Insert needle into 9th intercostal space in midaxillary line during expiration to avoid inferior border of lung
What are the two veins in the azygous system
Anterior intercostal vein
posterior intercostal vein
What are the veins in the anterior intercostal vein
- internal thoracic vein
what are the veins in the posterior intercostal veins
- Azygos vein on the right
- Hemiazygos vein on the left
What is the different between the azygos vein and hemiazygos vein
- Aygos vein on right – goes into the superior vena cava
- Hemiazygos veins on the left - can be multiple, much more variation than the axygous, drains into the Left brachiocephallic vein then into the superior vena cava
