LLL collapse
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This is left lower lobe collapse. Note the triangular, sail-like opacity behind the left heart border - this is the sail sign. The medial aspect of the left hemidiaphragm is obscured due to the collapsed lower lobe. In the second image there is left lower lobe collapse, the sail sign is less easy to see, but the hemidiaphragm is obscured and there is volume loss on that side. Note the ET tube is projecting into the right main bronchus. Refer to the article Patterns of lobar collapse for more information.