Superior Mediastinum Flashcards
What is the mediastinum?
The central compartment of the thoracic cavity lying between the two pulmonary cavities
It contains all thoracic viscera and structures minus the lungs.
How many parts is the mediastinum divided into?
Four parts: one superior and three inferior.
What bounds the superior mediastinum superiorly?
The thoracic aperture.
What anatomical landmark does the transverse thoracic plane represent?
The bifurcation of the trachea and the beginning and end of the arch of the aorta.
What are the subdivisions of the inferior mediastinum?
Anterior, middle, and posterior parts.
Which organ is located in the anterior part of the superior mediastinum?
The thymus.
What role does the thymus play before puberty?
Helps immune cells develop.
What happens to the thymus after puberty?
It undergoes gradual involution and is mostly replaced by fat.
What veins are included among the great vessels in the superior mediastinum?
Brachiocephalic veins and superior vena cava (SVC).
What arteries are included among the great vessels in the superior mediastinum?
Arch of the aorta and its major branches: brachiocephalic trunk, left common carotid artery, and left subclavian artery.
Where do the brachiocephalic veins form?
Posterior to the sternoclavicular joints by the joining of the internal jugular and subclavian veins.
At what level does the SVC enter the right atrium?
At the level of the 3rd costal cartilage.
Where does the arch of the aorta begin?
At the level of the sternal angle.
What does the ligamentum arteriosum represent?
An embryological remnant of the ductus arteriosus. Enable the flow of blood
What is the function of the vagus nerves?
Carry sensory, motor, and autonomic information to the mediastinum.
What does the right vagus nerve give rise to?
The right recurrent laryngeal nerve.
Where does the left vagus nerve give rise to the left recurrent laryngeal nerve?
At the inferior border of the arch of the aorta.
What do the phrenic nerves supply?
The diaphragm with motor and sensory fibers, and the pericardium and mediastinal pleura with sensory fibers.
What spinal levels contribute to the phrenic nerve?
C3, C4, and C5.
What can irritation of the phrenic nerve cause?
Referred pain to the dermatomes of C3, C4, and C5.
Where does the trachea end and divide into the right and left main bronchi?
At the level of the sternal angle marked by T4 and T5 junction.
What is the esophagus?
A fibromuscular tube that extends from the pharynx to the stomach.
What does the thoracic duct lie to the left of?
The esophagus.
What are the contents of the superior mediastinum from anterior to posterior?
- Thymus
- Great vessels
- Inferior continuation of the trachea
- Inferior continuation of the esophagus
- Thoracic duct and lymphatics trunks.
What separates the superior mediastinum from the inferior mediastinum?
The transverse thoracic plane.
What forms the right and left brachiocephalic veins?
The union of the internal jugular and subclavian veins
The veins are formed posterior to the sternoclavicular joints.
At what anatomical landmark do the brachiocephalic veins unite to form the SVC?
At the level of the inferior border of the 1st right costal cartilage
This is where the brachiocephalic veins combine.
How does the length of the left brachiocephalic vein compare to the right?
The left brachiocephalic vein is more than twice as long as the right
It passes from the left to the right side, anterior to the roots of the aorta’s major branches.
What is the primary function of the brachiocephalic veins?
To shunt blood from the head, neck, and upper limbs to the right atrium
This is essential for returning blood to the heart.
What is the role of the superior vena cava (SVC)?
Returns blood from all structures superior to the diaphragm, except the lungs and heart
It is critical for venous return to the heart.
Where does the SVC enter the heart?
At the right atrium
It ends at the level of the 3rd costal cartilage.
In which mediastinum does the SVC lie?
Right side of the superior mediastinum
It is anterolateral to the trachea and posterolateral to the ascending aorta.
What nerve lies between the SVC and the mediastinal pleura?
Right phrenic nerve
This nerve is important for diaphragm function.
What are the only branches of the ascending aorta?
Coronary arteries
They arise from the aortic sinuses.
Why is the ascending aorta considered a content of the middle mediastinum?
Because it is intrapericardial and lies inferior to the transverse thoracic plane
This anatomical positioning is important for surgical approaches.
Where does the arch of the aorta begin?
Posterior to the 2nd right sternocostal joint at the level of the sternal angle
This location is key for identifying the aortic arch in imaging.
What is the pathway of the aortic arch?
Arches superiorly, posteriorly and to the left, then inferiorly
It involves a complex anatomical course over the left lung.
What structure does the aortic arch descend beside?
The left root of the lung beside the T4 vertebra
This relationship is important for understanding thoracic anatomy.
Where does the aortic arch end?
By becoming the thoracic (descending) aorta posterior to the 2nd left sternocostal joint
This transition is critical for understanding blood flow dynamics.
Where does the arch of the azygos vein occupy its position?
On the right side of the trachea over the root of the right lung
The blood flows in the opposite direction to the aorta.
What is the ligamentum arteriosum?
The remnant of the fetal ductus arteriosus
It passes from the root of the left pulmonary artery to the inferior surface of the arch of the aorta.
