ICL 1.13: Mediastinum

Question 1

what is the mediastinum?

Answer 1

the anatomic region located between the lungs described as a partition separating the two pleural cavities

it serves as a corridor through which structures from the head and neck region connect with lower regions of the body and vice versa

it contains all the principal tissues and organs of the chest EXCEPT the lungs

Question 2

where is the manubriosternal joint?

Answer 2

the second rib!! it’s in-between T4 and T5

the sternal angle is at the 2nd rib!! aka Angle of Louis where the manubrium meets the body of the sternum

Question 3

what are the boundaries of the mediastinum?

Answer 3

it extends from the sternum back to the vertebral column

it’s bound laterally by the pericardium and the mediastinal pleurae

Question 4

which structures are in the mediastinum?

Answer 4

1. heart
2. thymus
3. portions of the esophagus and trachea

Question 5

what are the divisions of the mediastinum?

Answer 5

the mediastinum is split into a superior and inferior division at the sternal angle

the inferior division is split into the anterior, middle and posterior

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Question 6

where is the superior mediastinal compartment located?

Answer 6

it is located above the manubriosternal angle

its posterior boundary is made up of the first four thoracic vertebrae

above, the superior mediastinum is continuous with the neck

below it is continuous with both anterior and posterior mediastina

laterally it is limited by parietal (mediastinal) pleura

Question 7

what are the contents of the superior mediastinum?

Answer 7

1. thymus
2. aortic arch
3. superior vena cava
4. trachea
5. esophagus
6. right and left vagus nerve
7. phrenic nerves
8. thoracic duct

all of these pass through the superior mediastinum!! some of these go through multiple parts of the mediastinum

Question 8

where is the anterior mediastinal compartment located?

Answer 8

anterior mediastinal compartment is bordered by

1. the sternum anteriorly
2. the pericardial sac posteriorly

so basically it’s the part of the inferior mediastinum in front of the heart

Question 9

what are the contents of the anterior mediastinum?

Answer 9

1. sternopericardial ligament (it’s actually just fat)
2. fat
3. lymph nodes

Question 10

where is the middle mediastinal compartment located?

Answer 10

the borders are:

ventrally: the anterior mediastinal compartment
dorsally: the posterior mediastinum

Question 11

what are the contents of the middle mediastinum?

Answer 11

1. the pericardium
2. heart
3. phrenic nerves
4. pericardiacophrenic vessels
5. stems of great vessels

Question 12

where is the posterior mediastinal compartment located?

Answer 12

the borders are:

anteriorly: pericardial sac
posteriorly: the anterior surface of the vertebral bodies

Question 13

what are the contents of the posterior mediastinum?

Answer 13

1. descending aorta
2. azygous system of veins
3. vagus nerve
4. thoracic duct
5. lymph nodes
6. thoracic splanchnic nerves
7. esophagus

Question 14

where is the thymus located?

Answer 14

it’s a lymphoid organ located in the lower part of the neck and the anterior part of the superior mediastinum

it lies posterior to the manubrium and extends into the anterior mediastinum

it grows till you’re 5-6 years old then turns into fat after puberty!

Question 15

what are the terminal branches of the internal thoracic artery?

Answer 15

it ends at the sixth costal cartilage by dividing into musculophrenic and superior epigastric arteries

Question 16

what are the subdivisions of the aorta?

Answer 16

1. aortic arch
2. ascending aorta
3. descending aorta

the sternal angle is the landmark for these divisions!!!

Question 17

what is the ascending aorta?

Answer 17

from left ventricle to aortic arch mostly within pericardial sac

coronary arteries originate from the ascending aorta!

Question 18

what is the aortic arch?

Answer 18

above plane of manubriosternal angle

courses posteriorly and laterally

Question 19

what is the descending aorta?

Answer 19

continuation of arch on left side of vertebrae

course downward toward midline

reaches midline at T12 as it passes through diaphragm and goes to the abdomen!

Question 20

what are the 3 major branches of the arch of the aorta?

Answer 20

1. brachiocephalic (R)
2. left common carotid
3. left subclavian

Question 21

what are the 3 major branches of the descending aorta?

Answer 21

1. intercostal branches
2. mediastinal branches
3. esophageal branches

Question 22

what is the ligamentum arteriosum?

Answer 22

used to be the ductus arteriosus; a connection between the aortic arch and pulmonary trunk that closed off during development and turned into a ligament

it comes off the left pulmonary artery and connects to the aortic arch

Question 23

what are the great veins of the thorax?

Answer 23

1. inferior vena cava

pierces diaphragm at T8 and immediately enters pericardium and the heart

2. left brachiocephalic vein

formed by confluence of internal jugular and subclavian and courses obliquely to right in front of great arteries and joins right brachiocephalic v. behind intercostal space 1

3. right brachiocephalic vein

courses vertically behind the manubrium

4. superior vena cava

formed behind intercostal space 1 by two brachiocephalics and courses vertically to the right atrium; receives azygous vein

5. pulmonary veins

Question 24

what is the course of the thoracic duct?

Answer 24

it originates from the abdomen!

then it ascends through aortic hiatus of diaphragm then ascends between azygous vein and aorta and crosses to the left at T4-5 (sternal angle) to ascend behind the esophagus into neck joins confluence of internal jugular and subclavian veins

Question 25

what is the thoracic duct?

Answer 25

it drains all of body below diaphragm and left side of thorax!!

the remainder of the body is drained by the right lymphatic duct`

Question 26

where does the trachea bifurcate?

Answer 26

T4/T5 aka the sternal angle!

Question 27

what is the course of the esophagus?

Answer 27

it courses through superior and posterior mediastinum

continuous superiorly with pharynx in neck then pierces diaphragm at T10 to join stomach

upper portion in thorax is slightly left of midline because it’s pushed toward midline by aortic arch

then at the lower end it passes through diaphragm to left of midline

Question 28

what types of muscles compose the esophagus?

Answer 28

striated muscle in neck

smooth muscle in lower third

mixed in middle

Question 29

what is the blood supply of the esophagus?

Answer 29

esophageal branches of thoracic aorta which anastomose with inferior thyroid aa. and left gastric aa.

Question 30

which veins drain the esophagus?

Answer 30

submucosal plexus and surface plexus

drain to azygos system

may drain superiorly to inferior thyroid vv.

may drain inferiorly to gastric vein (portal-caval)

Question 31

which nerves innervate the esophagus?

Answer 31

vagus nerve from the esophageal plexus

striated muscle is innervated by the vagal recurrent branch

smooth muscle is innervated by the parasympathetic vagal

esophageal plexus surrounds the lower thoracic esophagus

Question 32

which nerves are located in the mediastinum?

Answer 32

1. phrenic nerve
2. vagus nerve
3. left recurrent laryngeal nerve
4. cardiac plexus of nerves
5. thoracic sympathetic trunks
6. thoracic splanchnic nerves
7. esophageal nerve plexus

Question 33

where are the left vs. right vagus and phrenic nerves located?

Answer 33

right phrenic nerve stays superficial while right vagus is deep

left phrenic and vagus nerves are both superficial!

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Question 34

which veins are part of the the azygos system of veins?

Answer 34

1. azygos vein
2. hemiazygos vein
3. accessory hemiazygos vein
4. left superior intercostal vein

they’re the veins that drain the intercostals and then as they drain the intercostals they end in the superior vena cava! basically it drains the whole thorax!

EXCEPT the left superior intercostal vein which drains directly into the left brachiocephalic vein

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