Curtain sign (lung ultrasound)

Last revised by Daniel J Bell on 10 Jun 2022

The curtain sign refers to the normal ultrasound characteristics of lung bases where the lungs are fully aerated. This is because the air in the costophrenic recess will cast a hyperechoic "air curtain" over the recess, obscuring the outline of the lateral diaphragm. The "air curtain" will also move in the craniocaudal direction, following the movements of the lung during respiration 1.

When the lateral diaphragm is fully visible or when there is a loss of normal movement of the "air curtain", lung pathology should be suspected 1.

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Cases and figures

  • Loss of curtain sign - pleural effusion
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