Skin fold mimicking a left simple pneumothorax

Chest radiograph in a patient with left ventricular failure and pulmonary edema. The left-sided skin fold that was initially mistaken for a pneumothorax displays a gradual lateral increase in opacity with an abrupt drop-off and a dark Mach band as its lateral contour (arrows) instead of a white visceral pleural line. Note the pulmonary vascular structures and the lung texture extending beyond the skin fold. These skin folds can develop when technologists insert the cassette under a supine patient from the opposite side of the skin fold and bunch up the skin of the back.