This post is in response to the post “Lung Ultrasound: Has it gone viral?”
To summarize, this was an 8-month-old girl who presented in respiratory distress. Point-of-care ultrasound was used to help determine the etiology of her symptoms and the following image was obtained:
Thank you to everyone who took the quiz!
19% of you guessed correctly that this video clip was consistent with a bronchiolitis/viral pneumonia. 41% guessed that this was a bacterial pneumonia, which is also potentially correct (as described in more detail below). The remaining 40% guessed that this was a pleural effusion or pneumothorax. No one thought that this was a clip of the thymus.
In our patient, the lung ultrasound demonstrated b-lines with subpleural consolidations. Typical bronchiolitis is associated with multiple B-lines and pleural abnormalities.
When there are subpleural consolidations, which appear as subpleural hypoechoic soft-tissue like masses measuring less than 1cm, this can be suggestive of either viral pneumonias or early bacterial pneumonia.
As mentioned above, B-lines with subpleural consolidations can be seen in viral pneumonias or early bacterial pneumonia. Larger subpleural consolidations that measure > 1 cm or take on a more tissue-like appearance (termed ‘hepatization’) are more commonly seen in bacterial pneumonias, but can be seen in some viral pneumonias and empyemas. What helps to differentiate bacterial pneumonias on ultrasound are the presence of bronchograms. Bronchi, which are not clearly visualized in normal lung ultrasounds, may be visualized in bacterial pneumonias when they are filled with secretions (“air bronchograms”) or fluid (“fluid bronchograms”). Preliminary studies have suggested that visualization of these bronchograms and larger consolidations can help to differentiate bacterial pneumonias from viral pneumonias.
Fluid is black, or anechoic, on ultrasound. When a pleural effusion is present, this can be seen as an anechoic collection between the visceral and parietal pleura.
In the RUQ/LUQ coronal views, the normal ‘mirror imaging’ artifact of the liver across the diaphragm is not seen with pleural effusions. Anechoic fluid above the diaphragm provides an excellent acoustic window through the lungs, which is typically filled with air. And as we know, air is the enemy of ultrasound! This enhanced acoustic window through the lungs allows us to visualize the deeper structures – namely the vertebral spine which is typically not visualized in the healthy normal lung. When we see the spine extend beyond the diaphragm, this is known as the ‘spine sign’ and can be a clue that a patient has a pleural effusion.
When there is air in between the pleural layers, such as in the pneumothorax, air scatters the image returning to the ultrasound probe and we are no longer able to see the lung sliding between the pleural layers. In B-mode, the shimmering of the pleural line is not visualized. In M-mode, the lack of visualized lung movement over time creates straight lines across the bottom half of the screen. Since there is no movement of either the intercostal muscles or the lung tissue over time, the M-mode image that is created is known as the ‘barcode sign’ or ‘stratosphere sign.’
The thymus is seen on ultrasound as a hypoechoic gland with a slightly grainy texture. What helps to differentiate normal thymus from bacterial pneumonias is the absence of air bronchograms. Aside from thymus, other organs that can be confused with consolidated lung tissue are the liver and spleen.
How to perform a lung ultrasound.
Lung ultrasound pitfalls.
Supporting literature to help differentiate between viral vs. bacterial pneumonia.
Think you already know all there is to know about lung ultrasound? Prove it.
If you want to see YOUR image included in the next Image of the Month, please email interesting stills and/or clips in addition to a small blurb on the patient to Lorraine Ng at PEMFellowscom@gmail.com.
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