The superior and posterior mediastinum week 2 Flashcards
What is a thoracic aortic aneurysm? What is it due to? What may happen to the thoracic aorta due to an aneurysm?
Aneurysms occur when there is a weakening in the wall of an artery and subsequent bulging or expansion of the wall. The weakened vessel wall is subject to tearing (dissection) which is a life-threatening condition when the aorta is affected. Aneurysms can occur in any part of the aorta. Thoracic aortic aneurysms are most often caused by atherosclerosis.
What is a hiatal hernia?
Condition where upper part of the stomahc bulges through the esophageal hiatus in the diaphragm.
What are the boundaries of the superior mediastinum?
anterior: manubrium of the sternum
posterior: T1-T4 vertebra
superior: oblique line passing from the jugular notch upward and posteriorly to the superior aspect of T1
inferior: imaginary line passing from the sternal angle to intervertebral disc btwn T4 and T5
lateral: bordered by mediastinal parts of the parietal pleura on either side
What are the main contents of the superior mediastinum? (12 things)
- thymus
- right and left brachiocephalic veins
- left superior intercostal vein
- superior vena cava
- arch of the aorta with its 3 branches: brachiocephalic trunk, left common carotid artery, and left subclavian artery (see essential anatomy)
- trachea
- esophagus
- phrenic nerves
- vagus nerves
- left recurrent laryngeal nerve
- thoracic duct
- azygous vein
Identify the structures of the superior mediastinum.
Where do the right common carotid and right subclavian arteries branch from? Where do the left subclavian and left common carotid arteries branch from?
What is the right most branch of the arch of the aorta?
From what parts of the body do the brachiocephalic veins return blood and into what vessel?
What are the only branches of the ascending aorta?
What side of the thoracic cavity (L vs R) does the descending aorta lie?
List the order of the pictured structures from anterior to posterior (superficial to deep).
- The right common carotid artery and right subclavian artery are branches of the brachiocephalic trunk which is one of the 3 branches of the arch of the aorta. The left common carotid and left subclavian arteries branch directly from the arch of the aorta.
- The brachiocephalic trunk is the right most branch of the arch of the aorta (then left common carotid, then left subclavian).
- The brachiocephalic veins return blood from the upper extremities (brachio) and the head (cephalic). They end as tributaries to the superior vena cava.
- The only branches of the ascending aorta are the right and left coronary arteries which is located in the middle mediastinum.
- The descending aorta lies on the left side of the thoracic cavity.
- Brachiocephalic veins (esp left) lie anterior to the arch of the aorta and its branches. Next is the trachea which is superficial to the esophagus. Note that the rings of the trachea are incomplete to allow for food to travel smoothly down the esophagus.
The ____ is the most anterior component of the mediastinum. What is the function of this structure? What vessels lie immediately posterior to this structure?
- thymus
- immune system organ, barely identifiable in elderly bc it involutes with age.
- right and left brachiocephalic veins
Identify the structures of the superior mediastinum. Note the vertebral level.
What spinal nerves compose the phrenic nerve? What 2 parts of the mediastinum may the be seen in?
Where does the vagus nerve come from? What 2 parts of the mediastinum may it be seen in?
Why does one of the veins in this cross-section look more oblique than the other?
- C3, C4, and C5 keep the diaphragm alive. Superior and middle mediastinum bc they have to course down to get to the middle mediastinum
- The vagus nerves come from the brainstem. They may be seen in the superior and posterior mediastina
- The left brachiocephalic vein looks more oblique than the right because it traverses the mediastinum to end as a tributary to the superior vena cava (along with the right brachiocephalic vein)
Identify the structures in this picture.
The ____ nerves course posterior to the root of the lung and into the posterior mediastinum.
The ____ vein comes up the posterior mediastinum. It receives blood from posterior intercostal veins and ends as a tributary to the SVC. It originates in the ____.
True or false: The trachea only exists in the superior mediastinum.
- vagus nerves
- azygos, abdomen
- True. It biforcates at the level of the sternal angle into right and left main bronchi (at that point is part of the lungs)
Identify the structures in this picture. Note their anatomical rships.
What is the course of the left recurrent larygneal nerve? Where does right recurrent larygneal nerve branch? What are these nerves branches of?
The recurrent laryngeal nerves are branches of the vagus nerves. The left recurrent laryngeal nerve branches from the left vagus nerve at the inferior margin of the arch of the aorta just lateral to the ligamentum arteriosum. It passes inferior to the arch of the aorta and ascends in a groove btwn the trachea and esophagus to enter the neck.
The right recurrent laryngeal nerve loops higher up-it wraps around the brachiocephalic trunk.
Note that mediastinal tumors can present with hoarseness of voice due to compression of this nerve.
What are the boundaries of the posterior mediastinum? What mediastinum is the posterior mediastinum actually continuous with in the body?
anterior: pericardial sac and diaphragm
posterior: bodies of mid and lower thoracic vertebra
superior: transverse plane extending from the sternal angle to the intervertebral disc btwn T4 and T5
inferior: diaphram
lateral: mediastinal parts of the parietal pleura on either side.
In actuality, the posterior mediastinum is continuous with the superior mediastinum.
What are the contents of the posterior mediastinum? What structures are not considered to be a part of the posterior mediastinum bc of where they lie in relation to the vertebral bodies?
- esophagus and associated nerve plexuses: esophageal plexus. right and left vagus nerves contribute fibers to this plexus-anterior and posterior vagal trunks
- thoracic aorta
- azygos system of veins (azygos, accessory azygos, and hemiazygos)
- thoracic duct and associated lymph nodes
- thoracic splanchnic nerves
The sympathetic trunks ARE NOT part of the posterior mediastinum bc they lie lateral (not anterior) to the vertebral bodies. This region is not named, they are just paravertebral structures.
What is the carina of the trachea? Where is this located?
What are the anatomical differences btwn the right and left main bronchi?
- The carina of the trachea is a ridge at the base of the trachea that separtes the openings of the right and left main bronchi. Also called trachea carina. Is at sternal angle.
- The right main bronchus is wider and straighter than the left main bronchus. The left main bronchus is more oblique. Ppl tend to aspirate into the right lung for this reason.
The esophagus, thoracic aorta, and IVC course through openings in/behind the diaphragm. At what vertebral level do each of these structures do so?
I 8 10 Eggs At 12
IVC: at level of T8
esophagus: at level of T10
thoracic aorta: at level of T12. turns into abdominal aorta
How does the esophagus receive sensory and motor innervation? How do the anterior and posterior vagal trunks arise?
- Via the vagus nerves (parasympathetic) and the sympathetic chain thorugh the esophageal plexus.
- Fibers that originated from each vagus nerve continue to course inferiorly along the esophagus toward the abdomen; however fibers of the left and right vagus nerves are now mixed resulting in the anterior and posterior vagal trunks. These fibers mix due to a 90 degree rotation of the esophagus from left to right. The anterior vagal trunk is composed mainly of fibers from the left vagus nerve. The posterior vagal trunk is composed of fibers mainly from the right vagus nerve. Both vagal trunks continue into the abdomen with the esophagus. Please see pg 100 of course notes for additional pic
Identify the branches of the thoracic aorta.
Where does the thoracic aorta begin (what vertebral level)?
What is the difference btwn how the right and left posterior intercostal arteries course after branching from the thoracic aorta?
The thoracic aorta begins at the lower edge of the T4 vertebra as a continuation of the arch of the aorta. Remember that it courses behind the diaphragm to enter the abdomen at T12 to become the abdominal aorta.
The right posterior intercostal arteries must course over thoracic vertebra (bc thoracic aorta is on the left side of the posterior mediastinum). This is a good way to tell them apart form posterior intercostal veins.
What veins are included in the azygos system of veins? Which veins drain blood from which parts of the mediastinum? To what vessels do they end as tributaries to?
azygos vein (right side of posterior mediastinum), accessory hemiazygos, and hemiazgos (both on left side. can remember accessory is first bc wear your accessories like earrings etc. on upper part of body)
The accessory hemiazygos vein drains the superior posterior mediastinum. The hemiazygos vein drains blood from the inferior posterior mediastinum. All of the azygos veins receive blood from posteior intercostal veins. The accessory hemiazygos and hemiazygos veins end as tributaries to the azygos vein which drains into the SVC.
Note that this system makes anastomotic connections with abdominal veins and is capable of returning blood from the lower part of the body to the heart if the IVC is blocked. Also note that some people do not have an accessory hemiazygos and/or hemiazygos veins.
What is the thoracic duct? Where does it begin and end? Where is it located?
- Main channel through which lymph from the majority of the body is returned to the venous system
- Begins at the cisterna chyli (a confluence of lymphatic trunks) in the abdomen and extends into the neck where it empties into the junction of the left subclavian and left internal jugular veins (note that right lymphatic duct empties into the junction of these same veins on the right side of the body)
- The thoracic duct is posterior to the esophagus and medial/to the left of the azygos vein
Where are the sympathetic chain/paravertebral ganglia located? How do they communicate with thoracic spinal nerves? What branches of nerves do the sympathetic ganglia give off and where are they located?
- located lateral to thoracic vertebra:paravertebral. not part of the posterior mediastinum.
- rami communicans
- greater splanchnic nerve (T5-T9), lesser splanchnic nerve (T10-T11), and least splanchnic nerve (T12). The splanchnic nerves lie anterior to the vertebral bodies and are therefore part of the posterior mediastinum
What structures drain into parasternal nodes and trunks?
anterior thoracic wall
breast
parietal pleura
diaphragm
upper abodminal wall
