Which radiological finding indicates pleural effusion?

The presence of fluid around the lungs is the hallmark sign of pleural effusion. In medical imaging, such as chest X-rays or CT scans, pleural effusion appears as an abnormal accumulation of fluid in the pleural space, which is the area between the lung and the chest wall. This accumulation can lead to displacement of the lung and may also cause blunting of the costophrenic angles on an upright X-ray.

In contrast, fluid in the lungs would typically indicate conditions such as pulmonary edema or pneumonia, which involve the lung parenchyma rather than the pleural space. A collapsed lung, known as pneumothorax, represents air in the pleural space and is a different pathological process entirely. The option referring to "none of the above" is not applicable since pleural effusion is a recognized condition with specific imaging characteristics that are adequately described by the correct option. Thus, fluid around the lungs directly correlates with the diagnosis of pleural effusion.