Pathophysiology.—Atelectasis is reduced inflation of all or part of the lung (,20). One of the commonest mechanisms is resorption of air distal to airway obstruction (eg, an endobronchial neoplasm) (,21). The synonym collapse is often used interchangeably with atelectasis, particularly when it is severe or accompanied by obvious increase in lung opacity.
Radiographs and CT scans.—Reduced volume is seen, accompanied by increased opacity (chest radiograph) or attenuation (CT scan) in the affected part of the lung (,Fig 8). Atelectasis is often associated with abnormal displacement of fissures, bronchi, vessels, diaphragm, heart, or mediastinum (,22). The distribution can be lobar, segmental, or subsegmental. Atelectasis is often qualified by descriptors such as linear, discoid, or platelike. (See also linear atelectasis, rounded atelectasis.)