Table 1 Line patterns seen in lung ultrasound and their corresponding clinical significance

A lines

A lines are ultrasound artifacts that are not related to any pathology.

These lines are horizontal in the ultrasound field and regularly spaced. They represent the ultrasound waves reflecting off of the pleural lining rather than returning directly back to the probe. This finding can be seen in normal lungs.

B lines

B lines are pathologic findings related to alveolar interstitial syndrome.

These lines are vertical and narrow, which project from the pleural lining to the edge of the ultrasound field. They are hyper-echogenic, distinct, and resemble either rays of sun shining through clouds or ‘comet tails’. When there are multiple B lines in the image, they are described as ‘lung rockets’.

Z lines

These can be seen in healthy patients as well as in those with a pneumothorax.

They resemble B lines but are shorter, broader, and not as clearly defined. They do not project to the edge of the ultrasound window but still arise from the pleural line.

E lines

Seen in subcutaneous emphysema or in the presence of echogenic foreign bodies.

These can be best described as comet tail artifacts that are superficial to the pleural lining.

V line

Seen in supine patients in the presence of pleural fluid.

The posterior thoracic cage (vertebral bodies and posterior ribs) is seen as an echogenic line extending cephalad to the diaphragm due to transmission of ultrasound waves through fluid to the posterior thoracic cavity.