Spectacular rounds this week lead by Sahar Ahmad of Stonybrook and hosted by Pierre at BI.
Sahar gave a great presentation on her didactic program for the critical care fellows at Stonybrook. She then presented a series of discussion inducing cases. Carl Kaplan (of Stonybrook not RUSH) presented an interesting case of ONSD ultrasound for hydrocephalus. Sam Parnia gave a presentation on the cardiopulmonary resuscitation research being done at Stonybrook on cerebral oximetry.
Some of the articles (with pmid and link) that came up in discussion were:
More lung ultrasound tips and examples from Drs. Jim Tsung and Brittany Pardue Jones!
Bacterial pneumonia will manifest as lung consolidation with air bronchograms. The A-line pattern of normal lung will begin to be replaced by B-lines in the area of affected lung:
Here we’ve highlighted the consolidation from the above video as well:
In contrast, subpleural consolidations and confluent B-lines are more suggestive of viral pneumonia.
So what do these look like?
and another example:
occur when multiple B-lines coalesce. In contrast, the next example demonstrates multiple discrete B-lines.
And now for something completely different
Z-Lines: Comet tails that arise from the pleural line but DO NOT make it to the bottom of the ultrasound screen. These are not B-lines. These artifacts have not been associated with any pathology, and they do not obliterate A-lines.
For more details on the sonographic appearance of viral lung pathology, check out this article by Jim Tsung.
Counter-intuitively, when insonating the lungs of healthy patients, we don’t “see” lung tissue. Instead we see and interpret artifacts arising from the pleural lines and the diaphragm. These artifacts change with pulmonary disease processes. In pneumonia, the airway spaces become inspissated with bacterial byproducts and consequently the sonographic appearance of lung tissue changes.
The transformation of lung tissue is termed hepatization: the lung tissue now appears similar to liver tissue.
This can be confusing in the lower lung fields, especially adjacent to the diaphragm because we use the mirror image artifact of the liver and spleen to indicate that lung tissue is normal. This mirrored, artifactual splenic or liver appearance could then be called pseudo-hepatization.
So, how do we differentiate hepatized lung versus pseudo-hepatized lung?
Never use a single image for your diagnosis, scan through area and convince yourself (then save a representative image or clip for QA).
Be systematic and scan down from the lung apices to the diaphragm.
Hunt for the diaphragm and use it as a dividing line between the lung and the abdominal organs.
Hepatized lung will often have a rim of fluid around it.
So we are scanning the left thorax in a patient with shortness of breath, in an effort to assess for pleural effusion. The following video was obtained:
The operator correctly noted the presence of a pleural effusion, and a bit of lung tissue can be seen towards the left side of the screen floating in fluid. In addition, there are THREE shadows evident, each from a different source. Can you spot them?
So let’s take these one at a time, with labels:
Is the easiest one. It extends almost from the first pixel at the top of the screen down to the far field. We can’t even see the characteristic echotexture of skin or subcutaneous tissue in the near field. There’s no contact here between the transducer and skin, possibly due to:
the probe not touching at all
clothing or an EKG lead getting in the way
not enough gel (the novice’s answer to everything but sometimes still true)
The most interesting one of the bunch. Probably two major factors at work here. First, this section of diaphragm is a particularly bright reflector so it can create a shadow behind it due to the sheer amount of reflection occurring. Second, the density difference between the diaphragm and pleural effusion is creating a refraction artifact, often referred to as an edge artifact. Beams of sound which were roughly parallel as they struck this interface get bent at different angles based on whether they hit the dense diaphragm or the less dense fluid. The space in between the formerly tightly spaced beams is displayed as blackness, or the absence of returning echoes.
That’s a rib shadow. Did you know that ribs grow back if you remove them?
With the proliferation of online educational modalities (blogs, educational websites, podcasts, twitter feeds) designed for rapid dissemination and translation of our basic Ultrasound knowledge to the bedsides around the globe, we must occasionally go back to the source – The Scientific Journal.
Listed below are several ultrasound-specific journals.
The Association of American Medical Colleges (AAMC) has written an article about ultrasound education at the medical school level. In the current edition of their widely distributed publication The Reporter, they describe programs at the University of South Carolina School of Medicine, University of California (Irvine) School of Medicine, and the Mount Sinai School of Medicine.
The article notes,
With rapid advancements in ultrasound technology, such scenarios as this are becoming more commonplace, as a handful of the nation’s medical schools make ultrasound training a standard part of the curriculum. And there is a push to encourage more schools to use ultrasound.
Thoracic sonography is one of the most rapidly growing areas of emergency and critical care ultrasound. One very important emerging indication is to assess for lung consolidation. The characteristic appearance of consolidated lung is very sensitive and specific for pneumonia, but novices should heed some important pitfalls in making the diagnosis.
Special thanks to Jim Tsung, MD, MPH and Brittany Jones, MD for their tips, videos, and ongoing research in this important field! For further reading on this topic, please see this article.
Pitfall #1 – confusing thymus for a consolidation
Normal thymus in sagittal view:
Thymus (top half of screen) and heart (bottom right). Don’t confuse thymus for lung consolidation. Note there are no air bronchograms, but thymus has a faint speckled appearance.
Normal thymus in transverse view:
Thymus (top half of screen) and heart (bottom right). Don’t confuse thymus for lung consolidation. Note there are no air bronchograms, but thymus has a faint speckled appearance
Pneumonia adjacent to Thymus in transverse view:
Lung consolidation with air bronchograms (top left) adjacent to normal thymus (speckled appearance on top right) with heart (bottom right)
Pitfall #2 – mistaking spleen for consolidation.
This is an important pitfall for everyone to know about. The same issue applies to the liver & stomach. The sensitivity of lung US for pneumonia rises >90% if this mistake is avoided.
Left lower chest- sagittal view:
Be careful scanning the left lower chest (left anterior and left axillary line) – air in stomach and spleen may look like pneumonia if you don’t realize that you have scanned inferior to the diaphragm and past the end of the pleural line. Most common error by novices.
Left lower chest- transverse view:
Be careful scanning the left lower chest (left anterior and left axillary line) – air in stomach and spleen may look like pneumonia if you don’t realize that you have scanned inferior to the diaphragm and past the end of the pleural line.
Pitfall #3- missing pleural effusion
Here are a few examples to refresh your memory.
Left pleural effusion:
Pleural effusion (anechoic wedge just beneath ribs and pleura)
Air in stomach
Do not confuse spleen and air in stomach for pneumonia.