Images Dr Ed Brentnall.
History:
A 22 year old man presents to ED with 1 week of a sore throat, a mild productive cough, fevers and rigors for 8 hours.
On examination : temperature 39.6, HR 143/min, RR 28/min, BP 133/60, Sats 98% on RA
Bloods were ordered. His WCC was 11.3, his CRP 1.5
A chest Xray was ordered and was reported as normal.
Whilst in ED he suddenly became tachycardic HR 150/min and had an episode of haemoptysis. Because of his normal Chest Xray a CT pulmonary angiogram was performed which showed a dense left lower lobe consolidation with mucous plugging and post obstructive atelectasis
A point of care ultrasound was performed. When we perform a point of care ultrasound the lung is divided into quadrants. Each lung is divided into 6 area – 2 anteriorly, 2 in the axillary region and 2 posteriorly . In order to cover the entire surface of the lung the probe is kept on the surface of the skin and moved up and down like a “lawn mower”
This is a clip of his lung ultrasound at R3
In the still image below identify 1,2.
What are we looking for when we focus on the structure indicated by the arrow labelled 1?
What is happening in zone A?
The arrow labelled 1 is pointing at the pleural line. This is the air (in the alveoli)/ tissue interface. Lung sliding is the movement that can be observed at the pleural line and is simply due to the sliding of the visceral pleura over the parietal pleura. Sometimes it is easier to see lung sliding by looking for shimmering at the level of the pleural line.
The arrow 2 is pointing towards the rib surface
Zone A shows artifacts. It is not possible to “see” beyond the pleural line when there is an air/tissue interface. The “dirty” white shadow is produced because of reverberation. It is a reverberation artifact. Sound waves are 99.9% reflected away from air. They are strongly reflected away and therefore bounce between the tissue interfaces above the pleural line. Because they are bouncing back and forth (reverberating) the returning echos take longer to return to the probe. The machine places the depth of an object on the screen according to the time it took for a sound wave to reach that object and then for the returning echo to return to the probe. The longer the time for the returning echo to reach the probe, the deeper the machine will place the object. Clearly if the sound wave has been bouncing to and fro (reverberating) then the returning echo will take longer to reach the probe and therefore the machine will place a dot on the screen deep to the air/tissue interface.
The absence of echos deep to the ribs is due to loss of energy of the sound waves due to absorption as they travel through bone. Some sound waves do get through bone but the returning echos get absorbed again on their way back to the probe causing an attenuation shadow.
This is a clip of his lung ultrasound at L6
In the following still image
- What are the arrows pointing to?
- Why does it occur?
- What are their significance?
The arrows are pointing to what are called B lines.
B lines are also reverberation artifacts but this time the reverberation is between alveoli and are due to fluid between alveoli. Sound waves are reflected strongly from the air/tissue interface and bounce back to and fro between the spaces between adjacent alveoli causing this artifact.
The following features have to be present before you can call this artifact a B line
- It must arise from the pleural line
- It is well defined and laser like
- It is hyperechoic
- It is long, spreading out without fading to the edge of the screen
- It moves with lung sliding
- To be pathological it is necessary to see 3 or more B lines between 2 ribs
B lines are found in all interstitial syndromes and has a wide differential which includes pulmonary oedema, bacterial/fungal/viral infection, pulmonary fibrosis, ARDS and pulmonary hemorrhage. It is the distribution of these B lines that gives you a clue as to what the pathology may be.
These B lines were present in L6. In lung ultrasound we turn off tissue harmonics which improves imaging because we want to highlight artifacts such as B lines. When we are looking for consolidation or fluid then we turn tissue harmonics back on because these are not artifacts and we will see them better by reducing artifacts.
Tissue harmonics is off in the following clip.
Explain what you see in the still image below.
There is an area of consolidation / atelectasis with surrounding pleural fluid. The ring down artifacts are reverberation artifacts in the same way as B lines. Note that they do not move with lung sliding because at that point there is no lung sliding.
Another clip was taken with the depth increased
What are the arrows pointing to in this still image?
1 and 2 shows pleural fluid. 3 shows the collapsed lung and 4 is the spine , 5 is the spleen.
What is the significance of the number 4 arrow
The spine shadow is important. When the lung is properly aerated ie there is no pleural fluid or consolidation, it is not possible to “see” beyond the diaphragm because of the air/tissue interface at the level of the diaphragm. The spine is therefore visible up till the costophrenic angle (blue arrow) and no further.
When fluid or consolidation is present sound waves will be transmitted right through to the spine so the spine will be visible. In this case you can see the spine extending beyond the costophrenic angle because fluid is present here.
Take home points:
This patient’s Xray was unremarkable. His lung ultrasound however clearly shows consolidation at the left base which is consistent with his CT findings.
Lung ultrasound is a sensitive tool to look for pathology in the emergency department and can be much more sensitive than Xray if done properly.