18. Demo: Thoracic Ultrasound Flashcards
Outline ultrasound
High frequency sound waves bounced off internal aging of organs and tissues via array of transducers to produce 2D images
Most commonly called B-mode or 2D mode
Outline the different ultrasound probes and why they are chosen
3.5MHz - Lower resolution images but increased depth of view
7-12MHz - High resolution images but limited depth of view
What is shown by an echogenic line on an ultrasound
This shows the visceral and parietal pleura at the lung edge
Where does the interlobular septa lie?
Between secondary pulmonary lobules
Outline M-mode ultrasound
One dimensional display of motion (M) of echo-producing interfaces displayed against time (T) along the second axis
Why is the paracoronal/parasagittal plan very useful for thoracic ultrasound?
It eliminates rib artefacts
Outline purpose of ultrasonography of the thorax
To detect pleural effusion and guide drainage
To differentiate sub-pulmonary from sub-phrenic fluid
To assess tumour invasion of chest wall and pleura
To guide pleural and lung biopsy
Identification of pneumothorax
Assessment of respiratory muscle function
Outline the respiratory muscle
Diaphragm
Internal intercostals
External intercostals
Accessory muscles (attached to sternum, clavicles and scapulae):
- SCM (sternocleidomastoid), scalenes, serratus, pectorals
Outline inspiration
Diaphragm contracts, moves down
Scalenes and SCM contract and elevate ribs and move sternum anteriorly
External intercostals (and interchondral portions of internal intercostals contract, elevate ribs
Outline expiration
Diaphragm relaxes, moves up
Scalenes and SCM relax, ribs move down and sternum drops posteriorly
External intercostals contract (aided by abdominal muscles), ribs move down
What does forced inspiration (sniff) testing test for?
It test for function of the phrenic nerve, by assessing the movement of the diaphragm
Normal: rapid caudal movement
Abnormal: paradoxical cranial movement
What is the diaphragm indistinguishable from on a CT scan?
The liver
Outline the sniff test
On sniffing the normally innervated diaphragm contracts and moves sharply downwards (towards the feet, caudally)
Outline the lung point sign
The lung point sign is a highly specific ultrasound sign of pneumothorax
It involves visualising the point where the visceral pleura (lung) begins to separate from the parietal pleural (chest wall) at the margin of a pneumothorax.
In the absence of pneumothorax, the two pleural layers slide along each other creating a series of comet tail artefacts on ultrasound referred to as the sliding sign
However when air sits in the pleural space and separates the two pleural layers no sliding is seen, referred to as absent sliding sign
The junction between sliding lung and absent sliding is known as the lung point and identification of this is near 100% specific for pneumothorax and also gives an indication of pneumothorax size by its location
It is not able to be found in all pneumothorax cases (sensitivity is around 65%) especially large pneumothoraces where the lung is collapsed and there is globally absent sliding
