Pneumothorax

This posterior-anterior (PA) radiograph of the chest reveals a left pneumothorax. The lateral border of the lung (arrows) no longer lies adjacent to the chest wall, and the lung parenchyma is contracted, accounting for the lung's abnormal appearance. Note the air and absence of lung markings along the left lateral border of the heart (small arrowheads) and the inferior and medial displacement of the left mainstem bronchus. The border of the scapula (large arrowheads) is sometimes mistaken for a pneumothorax.