B-line (ultrasound)

Last revised by Abdus Sattar on 17 Dec 2024

The B-line is an artifact relevant in lung ultrasonography. As originally described, it has seven defining features 1:

  • a hydroaeric comet-tail artifact

  • arising from the pleural line

  • hyperechoic

  • well-defined

  • extending indefinitely

  • erasing A-lines 

  • moving in concert with lung sliding, if lung sliding is present

B-line distribution corresponds with sub-pleural thickened interlobular septa, as demonstrated by CT, and are absent under normal conditions and present in alveolar-interstitial syndromes 2. Subpleural septal edema is postulated to provide a bubble-tetrahedron interface, generating a series of very closely spaced reverberations at a distance below the resolution of ultrasound which is interpreted as a confluent vertical echo which does not fade with increasing depth 3.

A few B-lines (<3/field of view) can often be found under normal circumstances, especially in the elderly, and around the base of the lungs 4.

Cases and figures

  • Case 1: B-lines
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