Imaging of pleural diseases.

The main pleural disorders are: effusion, thickening, masses and pneumothorax. Chest radiography is the first approach to evaluation of pleural disease; further evaluation is based upon ultrasounds (US), computed tomography (CT), and high-resolution CT (HRCT). The typical appearance of free pleural effusion is a homogeneous opacity with concave upper boundary; subpulmonic or intrafissural collections may also occur; the exudative effusions can be organized by adhesions between the pleural layers; consequently, loculated collections result. Radiographs allow us to assess the presence, amount and arrangement of effusions, but US and, especially, CT are needed to detect the modifications of the underlying pleura: circumferential thickenings, irregular and more than 1 cm thick are mostly malignant and denote mesothelioma or metastases: subtle and regular thickening is the typical appearance of fibrosis; a normal pleura does not exclude a malignant effusion. CT plays a major role in the diagnosis and management of empyema and in differentiating it from the pulmonary abscess. With CT it is also possible to differentiate the true pleural thickening from the false one due to a simple increase of extrapleural fat, and to disclose the activity of a fibrothorax through the detection of a small amount of fluid between the pleural layers. Pleural plaques are clearly visible by conventional radiography, especially with oblique views; US and CT are needed in the assessment of pleural tumors (fibroma, lipoma, fibro- and liposarcoma) and in determining the involvement of the lung and the chest wall. Pneumothorax is easily detected by conventional radiographs in the upright patient; when supine, the air collects in the anterobasal regions and particular projections are required; CT can reveal small amounts of air and is recommended in critically ill or trauma patients.