The skinfold artifact can mimic a pneumothorax on chest radiography and is caused by the added density of a skin fold against the image. It appears as a broad opacity laterally, outlined by a lucent line (Mach band effect) 2.
Radiographic features
Plain radiograph
The following features may help differentiate a skin fold from a pneumothorax:
visceral pleural is thin and sharp in contrast to broad skinfold
a skinfold does not follow the expected course of the pleura
skinfold often extends outside the hemithorax, pleura never does
increased peripheral lucency is present in pneumothorax
pneumothorax results in absent bronchovascular markings beyond the lung edge (occasionally markings visible if pneumothorax is loculated)
Differential diagnosis
The soft tissues of the medial arm can project over the lateral chest and mimic a pneumothorax and skin fold.