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The stratosphere sign (pneumothorax). Pneumothorax. On the left, this real-time image is frozen and cannot display abolished lung sliding, yet the use of M-mode (right image) clearly shows the absolute absence of movement at the level of the pleural line (black arrows): the stratosphere sign. Note again on the left image the A-line sign, indicating that only A-lines can be visualized in pneumothorax (white arrows). This again indicates air (see Fig. 2).
