Atelectasis: Opaque Hemithorax

Atelectasis resulting in an opaque hemithorax often indicates serious underlying disease including lung cancer or other tumors, with or without associated pleural effusion. Total lung atelectasis is usually caused by lung cancer obstructing a main bronchus, but can also result from mucus plugging, contralateral intubation of a main stem bronchus, bronchial stricture, or foreign body aspiration. A large amount of fluid and blood may be drawn into the collapsed lung with little or no loss of volume, resulting in a “drowned lung”. Chest radiographic findings of mediastinal shift toward or away from the opaque hemithorax, and associated findings pertaining to superior displacement of the ipsilateral hemidiaphragm and upper abdominal structures help establish volume loss as the etiology of the opaque hemithorax. Absence of these findings indicates preservation of volume in the ipsilateral hemithorax which may indicate the presence of a mass, an obstructing central lesion with associated drowned lung or a large pleural effusion with associated ipsilateral atelectasis. Pneumonectomy will result in an opaque hemithorax secondary to fluid filling of the pneumonectomy space. Unilateral pneumonia is a rare cause of opaque hemithorax.