Free layering pleural effusion

Panel A shows blunting of the right costophrenic sulcus (arrow) on an upright chest radiograph due to the presence of a pleural effusion. Panel B shows a right lateral decubitus radiograph from the same patient, and reveals layering of pleural effusion (arrowhead). Effusions thicker than 1 cm on decubitus views are usually large enough for sampling with thoracentesis.