Skin fold artifact

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The skin fold artifact can mimic a pneumothorax and is caused by the added density of a skin fold against the film appears as a broad opacity laterally, outlined by a lucent line (Mach band effect) .

Radiographic features

Plain radiograph

The following features can help differentiate a skin fold from a pneumothorax:

visceral pleural is thin and sharp in contrast to broad skin fold
a skin fold does not follow the expected course of the pleura
increased peripheral lucency is present in pneumothorax
pneumothorax results in absent bronchovascular markings beyond the lung edge