US of lungs

No sliding sign
• No “Comet tail” artifacts
• Absence of lung movement on M-mode (stratosphere sign
or bar code sign)

Ultrasound diagnostic criteria for pneumothorax are based on the
absence of the normal findings along the pleural interface

• Effusions
• Consolidation with pleural adhesions
• Chest tubes
• Advanced COPD

sliding sign can be absent in conditions other than Pneumophorax

hyperechoic structure. Free fluid will appear
anechoic (black) or hypoechoic (if the blood is clotted) superior to the diaphragm

Ultrasonography can detect a minimum of 20 cc of fluid in pleural space.
Diaphragm appears as a bright

transudate

exudate

hemothorax

There are three types of pleural effusion

Transudate

anechoic (black) and homogenous

Exudate

can have echoic features

Hemothorax

usually anechoic, but can have echogenic debris

Transudate is extravascular fluid

The primary cell types are
macrophages, lymphocytes and mesothelial cells. Transudate
usually appears clearer than exudates

Conditions that increase hydrostatic pressure in vessels;
• Left ventricular heart failure;
• Decrease in colloid oncotic pressure in blood vessels;
• Cirrhosis (cirrhosis leads to hypoalbuminaemia and decrease of
colloid oncotic pressure in plasma that causes edema);
• Nephrotic syndrome (also due to hypoalbuminaemia caused by
proteinuria)

The most common causes of
pathologic transudate include

vessel alteration during
inflammation (increased permeability, vasodilation). This results
in extracellular fluid of high protein content, with cell debris
present and high specific gravity (>1.020)

Exudate is the extravascular
fluid the accumulation of which is due to

proteins and cell debris
are absent

This is in contrast to
transudate where the extracellular fluid is an ultrafiltrate of blood
plasma and thus larger molecules such as

Hemothorax

blood in the
chest appears as an anechoic
area superior to the bright
echogenic hemidiaphragm

Anterior zone (1,2)

extrapleural air seen best
(i.e. pneumothorax)

Posterior/Lateral zones (3,4)

consolidations
and effusions seen best

All zones (1-4)

interstitial or alveolar fluid
visualized equally well

“Lung sliding”,
which represents the normal lung

Sliding of the visceral and parietal pleurae
with respiration results in the

“Comet tail” signs

Lung sliding” =

A lines: horizontal reverberation
artifact (A= air artifact)

equidistant horizontal artifact
indicating reflection of the pleura

B lines: vertical reverberation artifact

goes all the way down to the screen,
indicating that the two pleural layers are
in contact (1-4 B lines are normal)

• Blood
• Interstitial or alveolar edema
• Infection
• Contusion
• Tumor

Absence of A lines
Something has changed in the lung replacing air with substances that transmit sound waves

Absence of B lines

Pneumothorax
• Effusions
• Consolidation with pleural adhesions
• Chest tubes
• Advanced COPD

Consolidation

Loss of aeration of lung
Can be visualized on US in ~90% cases

Ultrasound findings:
• Allows ultrasound waves to be transmitted
deeper into thorax
• Lung tissue appears hypoechoic, wedge
shaped, poorly defined
• “Hepatization” in severe cases

Pneumonia

• Lung tissue appears hypoechoic with
numerous small hyperechoic splayed
horizontal lines
• Hepatic-like appearance
• Increased vascularity with Color Doppler

COVID-19 pneumonia

Multilobar distribution of abnormalities
 Bilateral
 Lower lobes (typically inferior)
 More than 2 lobes
• Irregular pleural line
 Unsmooth, thick, interrupted
With or without consolidations
• Minimal local pleural fluid around consolidations

Early stage and mild infection of covid

Focal B lines

Progressive stage and critically ill covid

Alveolar interstitial syndrome
(confluent lines, consolidations)

Ultrasonographic findings of COVID-19 pneumonia

Pleural line abnormalities (C-lines)
• B lines (multifocal, discrete, or confluent), (A/B profile)
• Confluent B lines (waterfall sign), (A/B profile)
• Small consolidations, subpleural (C profile)
• Both non-translobar and translobar consolidations (C profile)

Pulmonary edema

Multiple comet tails ( ) are seen when fluid replaces air.
Comet tails are reverberations of the sound waves, which are
trapped in the fluid-field interstitium or alveoli

Ultrasound criteria of pneumothorax

No comet-tail artifacts (absent B lines)
• “Bar-code” sign with M-mode

Transudate

Hypoechoic (black)
homogenous

Causes:
• CHF
• Cirrhosis
• Hypoalbuminemia
• Acute atelectasis
• End-stage kidney disease
• .......etc

Exudate

Can have echoic,
loculated features

Causes:
• Pneumonia
• Malignancy
• Infection
• Trauma
• Pulmonary embolism
• Pulmonary infarction.......etc

Hemothorax

Dependent debris

Causes:
• Trauma
• Vascular cause