Major imaging findings associated with complex loculated pleural effusions
Complex pleural effusions (often seen with exudative effusions) are often located in nondependent portions of the pleural space and do not shift freely in the pleural space on lateral decubitus chest radiography because of adhesions between the visceral and parietal pleurae. CT and MRI scans may also sometimes show associated pleural thickening and enhancement, internal septations, attenuation greater than that of water (i.e., >20 HU), increased signal intensity on T1-weighted images, or decreased signal intensity on T2-weighted images. Occasionally, loculated pleural fluid in the interlobar fissure may mimic a pseudomass on chest radiography, often appearing as a poorly marginated opacity on frontal chest radiography and as an elliptical opacity in the location of a major or minor interlobar fissure on lateral chest radiography.
