Tag Archives: Lung

The jellyfish sign: atelectasis

In moderate to large pleural effusions, it’s not uncommon to see lung atelectasis on the ultrasound. This collapsed lung within the effusion moves with respiration and appears like a jellyfish.

Important things to note:

Jellyfish sign favors atelectasis over pneumonia as the collapsed lung can change its shape with respiration whereas pneumonia is more firm.

It also favors transudative etiology of the effusion as the viscosity of exudative effusions tend to hamper mobility of the lung tissue.

Here are more examples

Pneumonia versus atelectasis: the differentiation can be difficult

As mentioned before, hepatization of the lung i.e., lung looking like liver tissue can occur in both pneumonia and atelectasis. Dynamic air bronchograms, when present, point toward pneumonia but static air bronchograms can be seen in both conditions. The differentiation can be very difficult at times and the management should be guided by the clinical picture.

Dynamic air bronchograms are not always as obvious as previously demonstrated. The probe angle needs to be adjusted as necessary to differentiate out of plane lung motion from moving air bronchograms. Other things to note:

  • More pleural effusion and less consolidated tissue suggest collapsed lung i.e., relaxation or passive atelectasis.
  • More consolidated tissue with less effusion, especially when the patient has fever or signs suggestive of infection points toward pneumonia even in the absence of dynamic air bronchograms.
  • Fibrin strands or loculated pleural effusion suggest infectious etiology.
  • Increased color flow in the consolidated tissue favors pneumonia while little to no flow suggests atelectasis.
Dynamic air bronchograms better seen in some planes. Note the Doppler flow in this case of pneumonia. Image courtesy: Dr. Lars Mølgaard Saxhaug

Here is another example of pneumonia with dynamic air bronchograms that require careful observation. Color flow is overall increased though there is some interference from tissue motion while the patient is breathing rapidly.

Pleural effusion and consolidation with fibrin stranding suggestive of infectious etiology. Image courtesy: Dr. Rohit Patel

Also note that small subpleural consolidations do not show typical dynamic air bronchogram pattern. For example, this lung ultrasound image obtained with the straight linear array probe (5–13 MHz) over right anterior chest demonstrates lung sliding and a small subpleural hypoechoic area with ragged margin separating it from the surrounding normal lung. This is described as the “shred sign” because of its distinctive irregular boundary with the normal lung.

B lines do not always indicate pulmonary edema

Diffuse B-line pattern can be seen in pulmonary edema of various causes, interstitial pneumonia and diffuse parenchymal lung disease (e.g. fibrosis). Whether you are dealing with pulmonary edema or fibrosis largely depends on the clinical context. However, findings such as irregular, fragmented pleural line, sub pleural abnormalities appearing as small hypoechoic areas and nonhomogeneous distribution of B-lines favor fibrosis. On the other hand, “focal” B-line pattern may be seen in pneumonia, atelectasis, pulmonary contusion, pulmonary embolism, pleural disease and malignancy.

The following loops were obtained from upper anterior zones on each side (R/L). While they show B-line pattern, the lower lung zones were normal and the patient was breathing comfortably on room air. This is a patient with interstitial lung disease and the B-line pattern represents fibrotic process. Also note that the pleural line is irregular.

Pneumonia and dynamic air bronchograms

In general, evaluation of an air-rich organ is a limitation of ultrasound because air scatters the ultrasound beam and does not allow proper visualization of the underlying structures. Therefore, normal lung tissue cannot be visualized unless it is consolidated. To give a rough idea, the estimated subpleural air content in pneumothorax, normal lung, interstitial syndrome, alveolar syndrome, atelectasis and pleural effusion is 100%, 98%, 95%, 10%, 5% and 0% respectively. Consolidations are highly fluid-filled, and over 95% reach the pleura, so ultrasound can image the pathology directly and lung appears like liver (= hepatization).

                     As we know, air bronchogram refers to the phenomenon of air-filled bronchi being made visible by the opacification of surrounding alveoli. It is almost always caused by an airspace disease, in which something other than air fills the alveoli. On a sonogram, air bronchograms appear as white structures (air is white on ultrasound). They are punctiform if transverse to the beam and linear if longitudinal. An air bronchogram which moves with respiration (= dynamic air bronchogram) excludes bronchial obstruction and helps distinguish between consolidation and atelectasis. In a hepatized lung, dynamic air bronchograms make pneumonia more likely, while static or no air bronchograms make atelectasis more likely. In a study, the dynamic air bronchogram had a specificity of 94% and a positive predictive value of 97% for pneumonia. However, the absence of dynamic air bronchograms does NOT rule out pneumonia. That’s when the overall clinical presentation becomes important to make a diagnosis.

Dynamic air bronchograms (moving white things) in a consolidated lung. Image courtesy: Dr. Hailey Hobbs@haileyahobbs
Another example of dynamic air bronchograms. Image courtesy: Dr. Michael I Prats@PratsEM

The following images show atelectasis with static air bronchograms. Pleural effusions are often associated with some degree of lung collapse at the bases.

Performance of lung ultrasound: Let’s talk numbers

The diagnostic accuracy of lung ultrasound for common pathologies such as pleural effusion, pulmonary edema, pneumothorax, and pneumonia is superior to chest radiograph and is comparable to chest CT scan. In addition, POCUS is helpful to evaluate the progress of lung pathology and response to treatment over time.

In ESRD patients on dialysis, lung ultrasound greatly outperforms the physical exam findings that we commonly rely on to ensure adequate ultrafiltration. It’s time to upgrade our physical exam!

B-lines in the lung: numbers to remember and scanning Zones

In routine clinical practice, 4 standard sonographic lung zones are evaluated on each side delineated using the parasternal line, anterior and posterior axillary lines and a horizontal line about the level of 3rd-4th intercostal space. Experts recommend scanning at least 1 posterior zone (posterior to posterior axillary line) on each side as well in supine patients when monitoring response to diuretic or ultrafiltration therapy.

Visualization of occasional B-lines, especially in the dependent zones of the lung is not abnormal. The presence of three or more B-lines per “rib interspace” in a longitudinal plane is abnormal and constitutes “B-pattern”. Generally, the observable distance between the lines should be no more than 7 mm.

B-pattern in two or more sonographic lung zones bilaterally is suggestive of “interstitial syndrome”, as demonstrated in Figure 1. This term encompasses pulmonary edema of various causes, interstitial pneumonia and diffuse parenchymal lung disease (e.g. fibrosis). In case of diffuse B-line pattern, whether you are dealing with pulmonary edema or fibrosis largely depends on the clinical context. However, findings such as irregular, fragmented pleural line, sub pleural abnormalities appearing as small hypoechoic areas and nonhomogeneous distribution of B-lines favor fibrosis. On the other hand, “focal” B-line pattern may be seen in pneumonia, atelectasis, pulmonary contusion, pulmonary embolism, pleural disease and malignancy.


There are several scoring systems, primarily described for research purposes, based on various scanning approaches. Commonly described scanning zones are illustrated in Figure 2. When evaluating an acutely dyspneic patient, examining 2 anterior zones might be enough, while more comprehensive approach is needed in chronically volume overloaded patients (e.g. CHF patient in the clinic, patient on maintenance hemodialysis etc.). Also note that the studied chest zones could include more than 1 rib interspace with a number of possible probe positions.

Pleural effusion: The ‘Spine sign’

Spine sign: visualization of the vertebral bodies in the thoracic cavity above the diaphragm – indicative of pleural effusion.

In the absence of pleural effusion, the spine is obscured by air in the lung, and is cut off at the diaphragm. Because fluid is a good transmitter of sound waves, spine is seen when there is fluid around the lung.