Loculated pleural effusion

The chest radiographic appearance depends on the site of the loculus, the amount of fluid and the radiographic projection. When seen en face it usually appears as an oval opacity, its margin partially well defined and partially ill defined. When viewed tangentially it is sharply defined on its convex pulmonary aspect. These appearances are similar to other pleural and chest wall masses. Fluid may collect within the loose connective tissue of the lung beneath the visceral pleura producing the so-called lamellar pleural effusion which is common in heart failure. There is a vertical band of soft tissue density between the lung and chest wall extending above the costophrenic angle which does not change in appearance with postural changes. The fluid is not a true pleural effusion as it lies outside the pleural space.

Chest ultrasonography and CT are used to differentiate pleural fluid from other pleural and chest wall lesions. On CT loculated fluid appears as a well-defined opacity of fluid attenuation between the fissures or adjacent to the chest wall, diaphragm or mediastinum. On ultrasound, loculated fluid collections are anechoic and delineated by a highly echogenic line at the lung interface.

CF - HM