What characteristic finding would you see on CXR for a large pleural effusion?

In the case of a large pleural effusion, the distinguishing characteristic finding on a chest X-ray (CXR) is the blunting of the costophrenic angles. This occurs because the pleural space collects fluid, which presents as an opaque area on the X-ray. Normally, the costophrenic angles should be sharp and well-defined; however, when there is fluid present in the pleural space, these angles become rounded or blunted due to the accumulation of the fluid.

This finding is particularly important because it indicates the presence of a significant volume of fluid in the pleura, which can help guide further management and decision-making in the evaluation of a patient's condition. Identifying fluid accumulation early can prompt additional diagnostic investigations, such as ultrasound or thoracentesis, to better evaluate the nature of the effusion and to initiate appropriate treatment.

Other findings, such as hyperinflation of the lung, free air under the diaphragm, or consolidation patterns, would indicate different pathological conditions not directly associated with pleural effusion. Hyperinflation typically relates to obstructive lung diseases like COPD, free air suggests perforation of a hollow organ, and consolidation patterns are indicative of lung infections or other pulmonary diseases.