The skinfold artifact can be mistaken for 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 indistinct medially and sharply outlined laterally (Mach band effect) 2,3.
Radiographic features
Plain radiograph
The following features may help differentiate a skin fold from a pneumothorax:
normal pleura is less than 1 mm thick
visceral pleural is seen as a thin line well-defined on both sides in contrast to the broad opacity of a skinfold which is well-defined laterally and ill-defined medially
a skinfold does not follow the expected course of the pleura
a skinfold often extends outside the hemithorax, pleura never does
peripheral hypertransradiancy is present in pneumothorax
pneumothorax results in absent bronchovascular markings beyond the lung edge (occasionally markings are visible if pneumothorax is loculated)
skin folds are frequently seen on portable chest radiographs - patients slide downwards after the cassette has been positioned
Differential diagnosis
The soft tissues of the medial arm can project over the lateral chest and mimic a pneumothorax and skin fold.