20. Demo: Thoracic ultrasound

Question 1

Ultrasound

Answer 1

High frequency sound waves bounced off internal organs and tissues via array of transducers to produce 2D images

Question 2

Most commonly used ultrasound

Answer 2

B-mode (2D mode)

Question 3

3.5 MHz ultrasound probe

Answer 3

Lower resolution images but increased depth of view
Curved array
Good for looking at organs deeper in body

Question 4

7-12 MHz ultrasound probe

Answer 4

High resolution images but limited depth of view
Linear array
Examining surface of body e.g. identifying veins or surface of lung

Question 5

Echogenic line

Answer 5

layers of visceral and parietal pleura at lung edge

Question 6

Describe the movement of lung pleura on an ultrasound

Answer 6

Visceral pleura slides over stationary parietal pleura as patient breathes

Question 7

What does “gliding pleura” or “sliding lung” show?

Answer 7

That we are looking at a normal lung

There is nothing between the lung edge and chest wall

Question 8

Describe ‘A’ lines

Answer 8

‘A’ lines run parallel to the lung edge, apparently within the lung but are reverberation artefacts
Move back and forth with ventilation (like an echo of the echogenic line)

Question 9

What may scanning the ribs aid?

Answer 9

Recognition of lung edge

Question 10

What are ‘comet tails’ or B line artefacts perpendicular to the lung edge?

Answer 10

Interlobular septa (boundaries between secondary pulmonary lobules)

Question 11

Describe interlobular septa in a patient with pulmonary oedema

Answer 11

Interlobular septa become enlarged and get distended

You would see many more comet tails than that of a person with a normal lung

Question 12

M-Mode ultrasound

Answer 12

1 dimensional display of motion (M) of echo-producing interfaces displayed against time (T) along the 2nd axis

Question 13

M-mode ultrasound of a normal lung

Answer 13

“Sea shore” sign

At lung edge (echogenic line), striking granular white line with sandy appearance behind (movement of lung artefact)

Question 14

Which plane is very useful for thoracic ultrasound as it eliminates the rib artefact?

Answer 14

Parasagittal plane/ Paracoronal plane

Question 15

List 6 uses of ultrasound of the thorax

Answer 15

Detect pleural effusion and guide drainage
Differentiate sub-pulmonary from sub-phrenic fluid
Assess tumour invasion of chest wall and pleura
Guide pleural and lung biopsy
Identification of pneumothorax
Assessment of respiratory muscle function

Question 16

How much fluid outside the lung wall is normal?

Answer 16

A tiny amount because it provides lubrication; allows visceral pleura to slide over parietal pleura.

Question 17

How much fluid outside the lung is abnormal?

Answer 17

Lots of pleural fluid e.g. 2cm on an ultrasound

Question 18

Describe muscular work in inspiration

Answer 18

Diaphragm contracts, moves down
Scalenes and SCM contract: elevate ribs and move sternum anteriorly- increases volume of hemithorax 
External intercostals (and interchondral portions of internal intercostals) contract, elevate ribs

Question 19

Describe muscular work in expiration

Answer 19

Diaphragm relaxes, moves up
Scalenes and SCM relax: ribs move down and sternum drops posteriorly
Internal intercostals (except interchondral portions) contract (aided by abdominal muscles): ribs move down

Question 20

What important nerve innervates the diaphragm?

Answer 20

Phrenic nerve

Question 21

Nerve roots of phrenic nerve

Answer 21

C3
C4
C5

Question 22

Positioning of phrenic nerve

Answer 22

Runs down anterior mediastinum, draped over front of heart to supply diaphragm

Question 23

What does damage to the phrenic nerve cause?

Answer 23

Diaphragmatic paralysis

Question 24

What do forced inspiration (sniff) tests asses?

Answer 24

Function of phrenic nerve

Question 25

Describe abnormal and normal sniff tests

Answer 25

Normal: rapid caudal movement (contracts and moves sharply downwards towards the feet)
Abnormal: paradoxical cranial movement

Question 26

What is the difference in scanning the diaphragm on a CT and an ultrasound?

Answer 26

CT: Diaphragm indistinguishable from liver
Ultrasound: Diaphragm seen well by echogenic stripe

Question 27

How is the diaphragm viewed? Why?

Answer 27

Diaphragm is obscured by aerated lung so must be looked at from below (sideways scan) (see diaphragm as it moves downwards)