Jellyfish sign (ultrasound)

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The jellyfish sign refers to the sonographic appearance of atelectatic lung "swimming" within a large pleural effusion. The mobility of the lung within pleural fluid implies an absence of lung consolidation and the absence of pleural adhesions . It is also suggestive of a transudative pleural effusion, as the viscosity of more exudative effusions may hamper free lung excursion .