Lecture 18: Anterior, Superior, and Posterior Mediastinum Flashcards
Define Mediastinum
Region of thorax located between the two pleural sacs and extends from the thoracic inlet to the diaphragm
What are the anterior and posterior bounds of the mediastinum
Anterior- sternum and costal cartilages.
Posterior- Bodies of thoracic vertebrae
What are the primary two divisions of the mediastinum
superior and inferior portions
What are the 3 subdivisions of the inferior mediastinum
anterior, middle, and posterior
What are the anterior and posterior boundaries of the anterior mediastinum
Anterior: Anterior surface of the pericardium
Posterior. Posterior surface of the costal cartilages and posterior surface of sternum
What does the middle portion of the mediastinum contain
Heart and pericardium
What does the posterior portion of the mediastinum contain
Posterior surface of pericardium, and anterior surface of vertebral bodies T5-T12
Vertebral levels of the superior mediastinum
T1-T4
Anterior and Posterior bounds of superior mediastinum
Posterior surface of manubrium and anterior surface of thoracic vertebrae T1-T4
List of structures in the anterior mediastinum
thymus gland, internal thoracic a.
What is the role of the thymus gland in the child, what happens as the individual ages
Makes antibodies, the gland in the aging individual no longer functions and turns to fat.
Where is the thymus gland located within the anterior mediastinum
between the two braciocephalic veins
At the 6th rib what does the internal thoracic a. break into
Musculophrenic a. and superior epigastric a,
What does the musculophrenic a. supply
diaphragm
what does the superior epigastric a. supply
rectus sheath
What is the internal thoracic a. a branch of?
Subclavian a.
What are two other arterial branches given off by the internal thoracic a.
anterior intercostal a- supply intercostal spaces
Periocariacophrenic a- supplies phrenic n.
Constriction of the aorta will result in rib notching due to what anastomose?
Internal thoracic and intercostal a.
What is the most anterior structure of superior mediastinum
thymus
For the ducts, arteries, and veins in the superior mediastinum, which are most anterior and posterior?
Veins- anterior
Arteries- intermediate
Ducts (trachea esophagus, thoracic duct)- Posterior
What structure in the superior mediastinum is as far lateral as possible
phrenic n.
Is the left recurrent laryngeal n. a part of the superior mediastinum? What about the right
Yes, the right however is not because it is in the root of the neck
Branches coming off the superior vena cava in the superior mediastinum
left and right brachiocephalic vein
Branches coming of the arch of the aorta in the superior mediastinum
Descending aorta, brachiocephalic a., left common coratid a. and Left subclavian a.
In the superior mediastinum, what direction are the veins and arteries directed?
Veins- right and arteries-left because the venous portion of the heart is to the left and the opposite is true for the arterial portion
What are the two branches off the brachiocephalic veins
Subclavian v. and internal jugular v.
How does Superior vena cava syndrome arise
Results from obstruction of the superior vena cava
What is a common cause of superior vena cava syndrome
Enlargement of lymph nodes from cancer
What are symptoms of superior vena cava syndrome
Redness to face and upper extremities due to the back up of blood from superior vena cava which dilates capillaries
What organ is present in both the superior and anterior mediastinum
thymus
What are the two portions of the aorta
Ascending and desending
At what point does the ascending aorta start to descend posteriorly
At the sternal angle
What does the descending aorta come into contact with
Trachea and esophagus
What would a lesion of the aorta also likely involve?
Trachea and esophagus because they are in contact with one another
What is the most common anomaly when it comes to branching off of the aorta
The vertebral artery may instead of coming off the subclavian will come off between the left common coratid a. and left subclavian a.
What is the only branch of the brachiocephalic a. that is in the superior mediastinum
thyroidea ima
what does the thyroidea ima supply?
Thyroid gland
What are the two branches of the brachiocephalic a.
right subclavian a and right common coratid a.
At way point does the right brachiocephalic a divide into the right subclavian a. and right common coratid a.
Posterior to the sternoclavicular joint
What part of the mediastinum contains the descending aorta?
Posterior
What is the point of bifurcation of the trachea called?
Carina
Where is the carina located
Sternal angle
In what lung are aspirated objects more likely to enter and why
Right lung because the right mainstream bronchus is wider and more vertical than the left.
Are primary bronchi in the superior mediastinum
no
Is the esophagus posterior or anterior to the trachea
posterior
Where does the thoracic duct begin
in the abdomen opposite SMA at the upper end of the cistern chyli
What are the regions of the body not drained by the thoracic duct?
The right upper extremity, right chest, right neck, and right side of face
What does the lymph from the thoracic duct drain into
the juncture between the left internal jugular v. and left subclavian v.
What drains the lymph from the right upper extremity, right thorax, right head and neck?
Right lymphatic duct
Where does the right lymphatic duct drain into the venous system
At the junction of the right subclavian and right internal jugular v.
Do the phrenic nerves descend into the superior mediastinum
Yes (From C3,4,5)
How can someones vocal cords be paralyzed?
By damaging the left recurrent laryngeal n (comes off vagus)
What nerve forms a plexus around the trachea
Vagus
Where does the left recurrent laryngeal n. course
around the left side of the ligament arteriosum under the arch of the aorta
Are the left and right recurrent laryngeal nerves present in the superior mediastinum?
Left yes right no. The right is at the root of the neck and loops between the esophagus and trachea
Since the left recurrent laryngeal n. is located in the anterior mediastinum (lots of lymph nodes) what are they prone to?
Paralysis of vocal cords caused by pinching the l. recurrent laryngeal n. from enlarged lymph nodes
What is another way the left recurrent laryngeal branch may be compromised?
aortic aneurism (the thoracic aorta is prone to these)
What are the two plexi that the left vagus nerve contributes to
The esophageal and cardiac autonomic plexus
Are the paired sympathetic chains also located in the superior mediastinum?
Yes
What are the contents of the posterior mediastinum
esophagus (with its vagal plexi), descending aorta, thoracic duct, azygos/hemiazygos/accessory azygos veins, and splanchnic nerves
Where are the 3 regions where the esophagus narrows
- Its origin
- at its midpoint where it is constricted by the aortic arch and left mainstream bronchus
- Inferiorly where it passes through the diaphragm
Where does the azygous vein lie?
To the right side of the vertebral column
Where does the azygous empty into
Superior vena cava
Which intercostal spaces are directly drained by the azygous vein
5-12
How is blood from intercostal spaces (2-4) indirectly drained into the azygous v.
Blood drains into the right superior intercostal vein, which empires into the azygous v.
Where does the hemiazygous v. begin?
At level of diaphragm
What intercostal spaces does the hemiazygous drain
8-12
Where does the accessory hemiazygous begin and end
Intercostal space T4-T7
Where is the thoracic duct positioned?
Between the azygous v. and the aorta
What are the 3 branches the descending aorta gives off
- Paired posterior intercostal a.
- bronchiol arteries
- Esophageal arteries
Why is the sympathetic chain present in the superior mediastinum but not the posterior mediastinum and the splanchnic n. are located in the posterior, which come off of the sympathetic chain?
Because as you travel down, the chain mosts posterior to the vertebral bodies (thus moving out of the mediastinum since the posterior border of the mediastinum is the anterior surface of the vertebral bodies)
To review: What are all of the components of the anterior mediastinum
Thymus and internal thoracic a.
To review: What are all of the components of the superior mediastinum
- Left and right brachiocephalic veins
- Ascending and arch of aorta
- Branches: Left brachiocephalic a., Left common coratid a., and left subclavian a. - Thoracic duct, esophagus, trachea
What vessels are located in the root of the neck
- Branches off of the left and right brachiocephalic veins: Subclavian v. and internal jugular v.
- Branches off left brachiocephalic a.: Right Subclavian a. and right common coratid a.
What are the structures in the posterior mediastinum
esophagus (with its vagal plexi), descending aorta, thoracic duct, azygos/hemiazygos/accessory azygos veins, and splanchnic nerves
Describe the location of the thymus
Sits between the two brachiocephalic v.
Describe the location of the internal thoracic a.
Run with the phrenic n and pericardiophrenic a. and v.
In the superior mediastinum, what is the arrangement for the three different ducts (thoracic, trachea, and esophagus)
Trachea (inferior to descending aorta), esophagus, thoracic duct
What vessels coming off of the aorta are most anterior? Most posterior?
Goes in alpha-order from anterior to posterior: Left brachiocephalic, left common coratid, and left subclavian
In the posterior mediastinum, where is the azygous v. located
Right side of vertebral column deep to the esophagus
Where is the thoracic duct
Sandwiched between the descending aorta and azygous v.
From what intercostal spaces do the two hemiazygous veins run?
Accessory hemiazygous- T4-T7
Hemiazygous- T5-12
What do the accessory and hemiazygous veins drain into?
Azygous
What are the 3 vessels the descending aorta gives off in the abdomen posterior to the diaphragm
- paired posterior intercostal a
- bronchial a.
- esophageal a.
Splanchnic nerves
Run from sympathetic chain towards the anterior vertebral column
List all the structures found in more than one segment of the mediastinum
- Aorta
- Thoracic duct
- Esophagus
- Vagus n
- Phrenic n.
What is related to the esophagus as it passes through the thorax
aorta, main stem (or primary bronchus), and the pericardium
Why can the phrenic n. be damaged during coronary bypass surgery
Because the phrenic nerve in the anterior mediastinum is glued to the heart
