The Mediastinum

Question 1

where does the mediastinum:

a) extend from?

b)

Answer 1

• extends from the thoracic inlet / aperture (from the clavicle and first rib) to diaphragm
• anteriorly: lies behind the sternum and costal cartilages back to the thoracic vertabrae
• bc attached to the diaphragm and contains hollow, air filled structures: mediastinum is highly mobile

Question 2

whats the vertebral postion of the sternal angle?

where in relation to ^ do the superior and inferior mediastinum lie?

Answer 2

sternal angle (aka transthoracic plane manubriosternal joint): T4/5

• *superior mediastinum:** superior to sternal angle: T1-T4/5
• *inferior medistinum:** terminates at the diaphragm

Question 3

what can change the position of mediastinum organs?

what is the difference in the postion of the:

a) arch of aorta
b) bifurcation of trachea
c) central tendon

between the supine and standing postion?

Answer 3

• gravity changes the position -> supine and standing positon changes them
• *- supine:**
  i) arch of aorta lies superior to transthoracic plane
  ii) bifurcation of trachea is transected by transthoracic plane
  iii) central tendon lies at the level of xiphisternal junction (T9 vert)

- standing:
ii) arch of aorta is transected to transthoracic plane
ii) bifurcation of trachea lies inferior by transthoracic plane
iii) central tendon may fall below level of xiphisternal junction (T19/10 vert)

standard is supine

Question 4

which structures are found in superior and inferior mediastinum?

Answer 4

• *superior mediastinum:**
• brachiocephalic veins and SVC
• Great vessels (asecending and arch of aorta)
• trachea
• oesphagus
• thymus gland
• phrenic nerve (x2) (C3,4,5)
• vagus nerve (cranial nerve 10) and recurrent laryngeal nerves (branches to the vagus
• thoracic duct and lympahtic trunks
• *inferior** mediastinum:
• heart
• oesophagus
• descending aorta
• IVC

Question 5

where on vertebral level does phrenic nerve lie?

where does it give somatic sensation to?

Answer 5

C3,4,5 - innervation to diaphragm

lies anteriorly

gives somatic sensation to pericardium, mediastinal pleura

Question 6

label 1-10 xox

Answer 6

Question 7

what do the following supply?

• right and left vertebral artery:
• thyrocervical trunk:
• internal thorcic artieries:

Answer 7

• right and left vertebral artery: brain stem and cerebellum
• thyrocervical trunk: Inferior part of the thyroid gland, parathyroid glands, larynx, pharynx, platysma, brachial plexus, deep cervical and shoulder muscles, skin of the neck and shoulders
• internal thorcic artieries: Skin and muscles of the anterior aspect of the thoracic cage and superior aspect of the abdominal wall, typical ribs, breasts, parietal pleura, sternum, pericardium and thymus.

Question 8

which cranial nerve is the vagus nerve?

what does it innervate?

Answer 8

- cranial nerve X (therefore part of parasympatheric NS)

- innervates:

i) oesophagus
ii) heart
iii) bronchi
iv) recurrent laryngeal loops back to innervate larynx:
- right reccurent laryngeal loops under right subclavian artery (higher than right)
- left reccurent laryngeal loops under the arch of aorta (lower than right)

Question 9

what happens as a result of phrenic nerve paralysis?

Answer 9

• results in elevation of the ipsilateral hemidiaphragm

Question 10

where does trachea run?

what is structure like?

where does bifurcation of trachea occur? name for this?

where does the aorta lie compared to the trachea?

Answer 10

- trachea: C6-T4

- u shaped cartilaginous ring

- bifurcation of trachea into primary bronchi = carina. at level of transthoracic plane T4/5

- aorta arches over left main bronchus and lung root

Question 11

where does the oesphagus sit?

compared to trachea?

how does it incline?

Answer 11

oesophagus:

• *- C6-T10
• **immediately posterior to trachea
• inclines to the left but compressed by the aortic arch (T4) and root of left lung (left main bronchus: T5-6)

Question 12

label pls xox

Answer 12

Question 13

Answer 13

Question 14

within the inferior mediastinum:

whats in the anterior mediastinum?
whats in the middle mediastinum?
whats in the posterior mediastinum?

Answer 14

anterior mediastinum: thymus
middle mediastinum: pericardium and heart
posterior mediastinum: primary bronchi, oesphagus, descending aorta, thoracic duct and zygous veins

Question 15

where are the surface anatomy landmarks for the superior, left, right and inferior borders of heart?

Answer 15

outline of the heart:

• superior border - 2nd left costal cartilage goes to superior border of third right costal cartilage
• right border: 3rd right costal cartilage down to sixth costal cartilage

- inferior border: right border to point close to mid-clavicular line (where get apex beat)

- left border: left inferior to superior margin

Question 16

which valves are where? xox

Answer 16

A = aortic valve
P = pulmonary trunk valve
T = tricuspid valve
M = mitral valve

Question 17

Answer 17

Question 18

desecribe the structure / layout of the posterior intercostal arteries (3)

Answer 18

- posterior intercostal arteries (3-12) come off at regular intervals from the descending aorta, except for the first two posterior intercostal arteries, which come from the costocervical trunk (branch that comes off subclavian arteries)

• the posterior intercostal arteries of the right side of the thoracic cage have to pass across the thoracic body, bc the aorta is located on the left.
• posterior intercostal arteries run in the superior part of intercostal space and run in the costal groove of the ribs, so that theyre protected by rib as run in to the superior part of intercostal space

Question 19

describe the layout of anterior intercostal arteries xo

Answer 19

- the anterior intercostal arteries are branches of internal thoracic arteries (which themselves come off the subclavians)

• anterior intercostal arteries run in the superior part of intercostal space. have a corresponding nerve & vein that lies in the costal groove
• smaller collateral branch in the inferior part of the intercostal space (not found in posterior region). not covered by the ribs

Question 20

how do the anterior and posterior intercostal artieres connect? which line does this occur?

what happens if damage to one of anterior / posterior arteries occurs?

Answer 20

anterior and posterior intercostal artieres connect via anastomosis @ mid-clavicular line

most of the intercostal region is supplied by the posterior intercostal arteries

if damage to one of anterior / posterior IC arteries, the collateral circulation can supply the rest of the thoracic cage

Question 21

Answer 21

Question 22

what is difference between the anterior and posterior intercostal arteries?

Answer 22

anterior IC arteries: much larger superior branch AND a smaller collateral inferior branch

posterior IC arteries: only single artery all the way down

Question 23

where do u take a thoracentesis (a procedure to remove fluid or air from around the lungs) from?

Answer 23

below the level of the lung

mid-axillary line - 9th intercostal space in the inferior intercostal space

Question 24

where would you do a thoracostomy (Thoracostomy is a minimally invasive procedure in which a doctor inserts a thin plastic tube into the pleural space — the area between the chest wall and lungs)

Answer 24

thoracostomy: mid-axillary line, inbetween 4th and 5th intercostal space

needle decompression: mid clavicular line, middle of 2nd / 3rd intercostal space

Question 25

awareness: the postion of the intercostal arteries, veins and nerves

Answer 25

Question 26

what do the anterior and posterior intercostal veins drain into?

Answer 26

venous drainage: uses **azygous system** - more veins & variations - **anterior intercostal veins** drain into **internal thoracic vein** - **posterior intercostal veins** drain into the **azygous vein on the right** (then the SVC), on **left** **goes into hemiazygos veins (**then into brachiocephalic)

Question 27

Answer 27