Respiratory: Anatomy - Overview of the mediastinum

Question 1

Describe the divisions of the mediastinum

Answer 1

Superior mediastinum: from superior thoracic aperture to thoracic plane
Inferior mediastinum: divided into anterior (anterior to pericardium), middle (pericardium and its contents), and posterior (posterior to pericardium)

Question 2

Describe the contents of the superior mediastinum from anterior to posterior

Answer 2

1. Thymus
2. Great vessels:
   - Veins anterior to arteries
   - Nerves
3. Cervical viscera and related nerves:
   - Trachea anterior to oesophagus
4. Lymphatic trunks (including thoracic ducts)

Question 3

At what landmark do the internal jugular and subclavian veins join to form the brachiocephalic veins?

Answer 3

Behind sternoclavicular joints

Question 4

At what landmark do the R and L brachiocephalic veins drain into the SVC?

Answer 4

Inferior border of R 1st costal cartilage

Question 5

At what landmark does the SVC join the RA?

Answer 5

3rd costal cartilage

Question 6

Describe the relationship of the SVC to the trachea and ascending aorta

Answer 6

Anterolateral to trachea
Posterolateral to ascending aorta

Question 7

The R phrenic nerve lies between which two superior mediastinal structures?

Answer 7

SVC and mediastinal pleura

Question 8

What is the diameter of the ascending aorta?

Answer 8

2.5cm

Question 9

What are the branches of the ascending aorta and where do they originate?

Answer 9

Coronary arteries from aortic sinuses

Question 10

At what landmark does the arch of the aorta begin?

Answer 10

Behind 2nd R sternocostal joint

Question 11

Describe the course of the aortic arch

Answer 11

Begins at level of right 2nd sternocostal joint
Ascends anteriorly to pulmonary artery and bifurcation of trachea
Reaches apex to left of trachea and oesophagua, passes over root of left lung
Descends posterior to root of left lung beside T4 vertebra
Becomes thoracic aorta behind left 2nd sternocostal joint at level of T4

Question 12

Describe the course of the azgous vein

Answer 12

Similar to arch of aorta but to R of trachea
Descends over right lung root

Question 13

Between what two structures does ligamentum arteriosum pass?

Answer 13

From left pulmonary artery to inferior arch of aorta

Question 14

Describe the course of brachiocephalic trunk in the superior mediastinum

Answer 14

Arises behind manubrium and L brachiocephalic vein, and anterior to trachea
Ascends to reach right side of trachea and R SCJ
Divides into right common carotid and subclavian arteries

Question 15

Describe the course of the left common carotid artery in the superior mediastinum

Answer 15

Arises posterior to manubrium, and posterior and to the left of the brachiocephalic trunk
Ascends anterior to left subclavian, and initially anterior than to the left of trachea
Enters the neck behind the L SCJ

Question 16

Describe the course of the left subclavian artery in the superior mediastinum

Answer 16

Arises posterior to left common carotid
Ascends lateral to trachea and left common carotid
Does not give off any branches within the mediastinum
Enters neck behind the L SCJ

Question 17

List the 10 nerves/plexuses of the superior mediastinum

Answer 17

Right and left vagus nerves
Right and left pulmonary plexuses
Right and left phrenic nerves
Right and left recurrent laryngeal nerves
Oesophageal plexus
Cardiac plexus

Question 18

Describe the course of the right vagus nerve in the superior mediastinum

Answer 18

Enters behind R SCJ and R brachiocephalic vein, anterior to R subclavian artery
Gives off R recurrent laryngeal
Runs posteroinferiorly to right of trachea, then passes behind R brachiocephalic vein, SVC and R lung root
Divides to form R pulmonary plexus
Then exits as single trunk before contributing to the oesophageal plexus
Similarly exits oesophageal plexus as single trunk before contributing to the cardiac plexus
Enters abdominal cavity as anterior and posterior trunks via the oesophageal hiatus

Question 19

Describe the course of the right recurrent laryngeal nerve in the superior mediastinum

Answer 19

Comes off vagus nerve and hooks around R subclavian artery
Ascends between oesophagus and trachea

Question 20

Describe the course of the right phrenic nerve in the superior mediastinum

Answer 20

Enters superior mediastinum between R subclavian artery and R brachiocephalic vein
Passes laterally to R brachiocephalic vein, SVC and pericardium over RA
Passes anterior to R lung root and descends to R of IVC, entering abdomen via caval opening

Question 21

Describe the course of the left vagus nerve in the superior mediastinum

Answer 21

Enters superior mediastinum between L common carotid and subclavian arteries
Diverges posteriorly from L phrenic nerve to the left of the aortic arch, separated laterally by L superior intercostal vein
Curves medially at inferior border of aortic arch and gives off L recurrent laryngeal nerve
Passes posterior to L lung root and divides to form L pulmonary plexus

Question 22

Describe the course of the left recurrent laryngeal nerve in the superior mediastinum

Answer 22

Given off by L vagus nerve
Hooks around aortic arch, lateral to ligamentum arteriosum
Ascends between oesophagus and trachea

Question 23

Describe the course of the left phrenic nerve in the superior mediastinum

Answer 23

Enters superior mediastinum between L common carotid and subclavian arteries, and origin of L brachicephalic vein
Crosses left surface of aortic arch anterior to L vagus and passes over L superior intercostal vein (vagus passes behind and medially)
Descends anterior to L lung root and runs along pericardium over LA/LV
Pierces diaphragm to L of pericardium

Question 24

Where does the trachea begin?

Answer 24

Below cricoid cartilage at C6, as a continuation of the larynx

Question 25

Describe the passage of the trachea in the superior mediastinum

Answer 25

Descends anterior to oesophagus and enters slightly to the right before bifurcating at T5

Question 26

What is the level of the tracheal bifurcation (carina)? How does this change with respiration?

Answer 26

T5 Stretches in full inspiration and may reach T6

Question 27

Describe the structure of the trachea

Answer 27

15-20 horseshoe-shaped hyaline cartilages Gaps in rings at back with trachealis (smooth muscle) High content of elastic fibres

Question 28

Four anatomical features of the trachea and their functions

Answer 28

Cartilage maintains airway patency Cilia clear debris Goblet cells secrete mucus to trap particles Secretions humidify air

Question 29

Describe the lymphatic drainage of the trachea

Answer 29

Posteroinferior group of deep cervical lymph nodes Pre and para tracheal lymph nodes

Question 30

Describe the nerve supply of the trachea

Answer 30

Vagal and recurrent laryngeal nerves Also receives sympathetic innervation

Question 31

Describe the posterior, lateral and anterior relations of the trachea

Answer 31

Posterior: oesophagus, recurrent laryngeal nerves Anterior: L brachiocephalic vein, thymus, manubrium Lateral: carotid sheaths, lateral lobes of thyroid

Question 32

How long are the cervical and thoracic portions of the trachea?

Answer 32

~5cm each

Question 33

Describe the structure of the oesophagus

Answer 33

Fibromuscular tube extending from pharynx to stomach

Question 34

What type of muscle lines the proximal vs distal oesophagus?

Answer 34

Proximal half: striated skeletal muscle Distal half: smooth muscle

Question 35

What type of epithelium lines the proximal vs distal oesophagus?

Answer 35

Proximal: stratified squamous Distal: columnar

Question 36

What is the total length of the oesophagus?

Answer 36

25cm

Question 37

Describe the course of the oesophagus through the mediastinum

Answer 37

Begins at cricoid cartilage (C6) Enters superior mediastinum anterior to vertebral bodies T1-4 and posterior to trachea Inclines to left but pushed back to median by aortic arch Compressed by L lung root, with thoracic duct lying to its left Inclines to left again and crosses over aorta distally Exits diaphragm via oesophageal hiatus (T10) Ends at cardiac orifice of stomach (T11)

Question 38

What forms the three oesophageal impressions?

Answer 38

1. Aortic arch 2. Left main bronchus 3. Diaphragm

Question 39

What nerve supplies the oesophagus?

Answer 39

Vagus nerve

Question 40

Describe the blood supply and venous drainage of the upper, middle, and lower thirds of the oesphagus

Answer 40

Upper: interior thyroid artery, brachiocephalic veins Middle: oesophageal branches of thoracic aorta, azygos vein Lower: branches of L gastric artery, tributaries to L gastric vein -> portal vein

Question 41

What it the pathophysiology of oesophageal varices in cirrhosis?

Answer 41

Cirrhosis leads to portal HTN Portal HTN -> increased pressure through L gastric tributaries draining oesophageal veins -> oesophageal varices

Question 42

Describe the borders of the posterior mediastinum

Answer 42

Anterior: pericardium and diaphragm Posterior: T5-12 vertebrae Superior: thoracic plane Between parietal pleura of the two lungs

Question 43

Five contents of the posterior mediastinum

Answer 43

1. Thoracic aorta 2. Thoracic duct and lymphatic trunks 3. Posterior mediastinal lymph nodes 4. Azygos and hemi-azygos veins 5. Oesophagus and oesophageal nerve plexus

Question 44

Explain the concept of the "planes" of aortic branches

Answer 44

Anterior: midline unpaired branches to gut and its derivatives (including oesophagus in the thorax) Lateral: paired visceral branches to organs other than the gut and its derivatives (including bronchial in the thorax) Posterolateral: paired parietal to body wall

Question 45

What are the 6 branches of the thoracic aorta? How many of each are there? Which are exceptions to the concept of "planes" of aortic branches and why?

Answer 45

1. Posterior intercostal (9) and subcostal arteries 2. Oesophageal arteries (4-5) 3. Bronchial arteries (1-2) 4. Mediastinal branches* 5. Pericardial branches* 6. Superior phrenic arteries** * exception: arise anteriorly but do not supply gut and its derivates ** exception: supplies part of body wall but arises anterolaterally (instead of posterolaterally)

Question 46

What is the thoracic duct and what parts of the body does it drain?

Answer 46

Largest lymphatic channel in the body Carries all lymph except that from the superior R quadrant (which drains to the R lymphatic duct)

Question 47

Describe the course of the thoracic duct

Answer 47

Starts at cisterna chyli at the level of T12 Runs behind R crus and to R of aorta, ascends through aortic hiatus into mediastinum Runs behind oesophagus Crosses midline to L at T4-6 Enters venous system somewhere at confluence of L subclavian and internal jugular veins (origin of L brachiocephalic vein)

Question 48

Which other three trunks does the thoracic duct receive in the mediastinum?

Answer 48

Subclavian Jugular Bronchomediastinal

Question 49

At what vertebral level does the thoracic duct cross the mediastinum to the left?

Answer 49

Around T4-6

Question 50

Which hiatus does the thoracic duct ascend through to enter the posterior mediastinum?

Answer 50

Aortic

Question 51

What venous drainage is received by the azygos vs the hemiazygos veins?

Answer 51

Azygos: posterior intercostal veins (except the inferior three), vertebral venous plexuses, mediastinal veins, bronchial veins, oesophageal veins Hemiazygos: inferior three posterior intercostal veins, inferior oesophageal veins, several small mediastinal veins

Question 52

Describe the course of the hemiazygos vein

Answer 52

Arises from posterior IVC and/or renal vein, with additions on its L side from subcostal and ascending lumbar veins Ascends on left side of vertebral column to level of T9 before crossing (posterior to aorta, thoracic duct and oesophagus) to join the azygos

Question 53

At what level does the accessory hemiazygos arise and where does it descend to?

Answer 53

Medial 4th/5th intercostal space Descends to level of T5-8

Question 54

Describe the relations of the sympathetic trunks in the posterior mediastinum

Answer 54

In superior thorax: lie against head of ribs In mid-thorax: lie against costovertebral joints In inferior thorax: lie against sides of vertebral bodies

Question 55

Four (or five) contents of anterior mediastinum

Answer 55

1. Sternopericardial ligaments 2. Fat 3. Lymphatic vessels and (few) lymph nodes 4. Branches of internal thoracic vessels (In children/infants: 5. Inferior part of thymus)

Question 56

How long is the thoracic duct?

Answer 56

45cm