Atelectasis are according to their aetiology divided into the obstructive or compressive. Compression atelectasis results from compression of previously well-aerated lung parenchyma by pressing air out of alveoli and airways and its resorption. Thus, lungs transform from well-aerated structure, causing ultrasound artefacts, to airless structure available to “real” ultrasound imaging. Aetiology may be determined as compressive or obstructive based on the size and behaviour of an atelectatic part of the lung, characteristics of the boundary between aerated and airless lung, shape of the outer margin of atelectasis and amount of eventual pleural effusion.


Following sequence displays typical signs of compression atelectasis:

  • reduction of lung parenchyma
  • atelectasis volume is smaller than effusion volume
  • the concave boundary between atelectasis and effusion
  • quite a sharp border between atelectasis and aerated lung
  • jellyfish sign


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