| Sonographic findings | Definition | Clinical significance |
| Lung sliding | Shimmering movement synchronous with respiration at the pleural line indicating sliding of the visceral pleura against the parietal pleura (refer to "Normal lung ultrasound findings" supplemental content). | - Present in normal lung or in pathologic conditions that do not affect ventilation
- Absent or reduced when visceral pleura does not slide against parietal pleura: apnea, inflammatory adherences, loss of lung expansion (overinflation/distension or severe bullous disease), decrease in lung compliance, airway obstruction/atelectasis, pleural symphysis, endobronchial intubation
- Absent when visceral and parietal pleura are separated (ie, pneumothorax; refer to "Pneumothorax" supplemental content)
|
| Lung pulse | Subtle, rhythmic movement of the lung parenchyma at the cardiac frequency from transmission of heartbeat vibrations through the lung tissue (refer to "Normal lung ultrasound findings" supplemental content). | - Present in normal lung and conditions with minimal effect on lung aeration (eg, pulmonary embolism)
- Absent or reduced when lung aeration is significantly increased (eg, bullous disease, overinflation/distension)
- Absent when visceral and parietal pleura are separated (ie, pneumothorax; refer to "Pneumothorax" supplemental content)
- Increased in conditions associated with increased lung density (refer to B-lines and interstitial syndrome)
NOTE: Identification of lung pulse in the context of absent lung sliding is considered a sign of lack of ventilation as seen in apnea, selective intubation, airway obstruction (foreign body, mucous plugging, etc) |
| A-lines | Hyperechoic horizontal lines at increasing depth separated by same distance as that between the probe and the pleural line. Considered reverberation artifacts arising from the strongly reflective interfaces of the probe and pleural line (refer to "Normal lung ultrasound findings" supplemental content). | - Present when air is homogeneously distributed below the pleural line:
- Normally aerated lung
- Pneumothorax
- Pathologic conditions with minimal effect on lung aeration (eg, acute pulmonary embolism, asthma/acute COPD exacerbation, early phases of airway obstruction/atelectasis)
- Absent or reduced when:
- Increased lung density and nonhomogeneous distribution of air
- Nonperpendicular angulation of the ultrasound beam with the pleural line (refer to "Normal lung ultrasound findings" supplemental content)
|
| B-lines and interstitial syndrome | Discrete laser-like, vertical, hyperechoic artifacts that arise from the pleural line, extend to the bottom of the screen without fading, and move synchronously with lung sliding (refer to "B-lines" and "Lung recruitment" supplemental content).[1] Three or more B-lines/intercostal space (sagittal scan) represent a positive region of increased lung density:[1] - Normal aeration: fewer than two isolated B-lines/intercostal space
- Moderate loss of lung aeration (B1 pattern): presence of ≥3 well-defined spaced B-lines/intercostal space
- Severe loss of lung aeration (B2 pattern): multiple coalescent B-lines/intercostal space[2,3]
Vertical artifacts at the transition from consolidated to normally aerated lung ("shred sign") represent the same physical and pathophysiologic phenomenon as B-lines, although not defined as such.[1] | - Present in conditions associated with increased lung density and involvement of alveolar units in close relationship with visceral pleura such as:
- Lung deflation (ie, atelectasis)
- Normal pattern (if isolated at lung bases)
- Increased lung weight:
- Extra vascular lung water (eg, cardiogenic or nonhydrostatic pulmonary edema – ARDS, idiopathic interstitial pneumonias, lung consolidation, pneumonitis, pulmonary infarct)
- Pus (eg, infection, pneumonitis, lung consolidation)
- Blood (eg, alveolar hemorrhage)
- Protein/collagen (eg, idiopathic interstitial pneumonias, alveolar proteinosis, lung consolidation, pulmonary infarct)
- Cells (eg, primary or metastatic lung cancer)
- Lipids (eg, lipoid pneumonia)
- Absent when visceral and parietal pleura are separated (ie, pneumothorax; refer to "Pneumothorax" supplemental content) and in normally aerated lung
|
| Short vertical artifacts (also known as Z-lines or comet tails) | Vertical artifacts that originate from and move with the pleural line but fade quickly; do not obscure A-lines (refer to "Normal lung ultrasound findings" supplemental content). | - Present in normal lungs
- Absent when visceral and parietal pleura are separated (ie, pneumothorax; refer to "Pneumothorax" supplemental content)
|
| Lung point | Presence of lung sliding, pulse and/or vertical artifacts on one side of an image with the absence of these findings on the other side. | - Present and very specific in pneumothorax, representing transition point at which partially collapsed lung contacts the parietal pleura during respiration (refer to "Pneumothorax" supplemental content)
- Absent in presence of large pneumothorax causing complete lung collapse (not a highly sensitive finding)
|
| Pleural line abnormalities | Any deviation from the normally appearing thin, smooth, and continuous hyperechoic line including thickening, coarse irregularities, and the presence of small subpleural consolidations (refer to "B-lines" and "Lung consolidation" supplemental content). | - Present in association with several inflammatory conditions (eg, ARDS, infection, pneumonitis, idiopathic interstitial pneumonia, and other interstitial lung diseases)
NOTE: False positive pleural line abnormalities when ultrasound beam not perpendicular to the pleural line |
| Lung consolidation | Anechoic or tissue-like image (hepatization) arising from the pleural line that is limited in depth by an irregular border (shred sign). Represents severely increased lung density with (almost) complete loss of aeration (refer to "Lung consolidation" supplemental content). | - Present in same conditions associated with B-lines and interstitial syndrome, as the extreme spectrum of increased lung density
|
| Air bronchogram | Hyperechoic spots or branch-like structures seen within consolidated lung: - Static air bronchograms
- Dynamic air bronchograms (moving with the respiratory cycle; refer to "Lung consolidation" supplemental content)
| - Present within areas of lung consolidation (dynamic air bronchograms) or atelectasis (if obstruction atelectasis, static air bronchograms)
|
| Spine sign | Discontinuation of the transverse processes of the spine above the diaphragm from the presence of normally aerated lung tissue preventing their visualization (negative spine sign; refer to "Normal lung ultrasound findings" supplemental content). | |
| Curtain sign | Phenomenon at the lung base, where diaphragm, liver/spleen, and spine disappear on inspiration due to lung descent and reappear on expiration as the lung ascends. | |
| Pleural effusion | Anechoic (fluid) collection between the parietal and visceral pleura (refer to "Normal lung ultrasound findings" and "Pleural effusion" supplemental content). Associated with positive spine sign and absent curtain sign (refer to "Pleural effusion" and "The importance of spine identification in the assessment of lung base for detection of pleural effusion" supplemental content). | - Present most often in supradiaphragmatic regions; complex or loculated collections may be elsewhere
NOTE: Ultrasound cannot differentiate the nature of the pleural effusion (eg, hemothorax, transudate, exudate), although visualization of mobile echoic particles or septa is highly suggestive of complex effusion (eg, empyema; refer to "Pleural effusion" supplemental content) |
