CT scans.—This finding is a thin curvilinear opacity, 1–3 mm in thickness, lying less than 1 cm from and parallel to the pleural surface (Fig 68). It corresponds to atelectasis of normal lung if seen in the dependent posteroinferior portion of lung of a patient in the supine position and is subsequently shown to disappear on CT sections acquired with the patient prone. It may also be encountered in patients with pulmonary edema (132) or fibrosis (other signs are usually present). Though described in the context of asbestosis, this finding is not specific for asbestosis. [Fleischner Society]