What imaging finding would indicate a potential need for intervention in the presence of a large pleural effusion?

Blunting of the costophrenic angle is a significant imaging finding that suggests the presence of a large pleural effusion. This finding indicates that the fluid has accumulated in the pleural space, causing the normally sharp angle between the diaphragm and the ribs to become rounded or obscured. When the costophrenic angle is blunted, it suggests that there is enough fluid accumulation that may require intervention, such as thoracentesis or drainage.

In the context of a pleural effusion, decreased lung volume could be a secondary effect, but it is not a definitive indicator for intervention. The addition of infiltrates might indicate other lung conditions, and the normal diaphragm position suggests that the effusion is not significant enough to displace the diaphragm, which would indicate a lesser urgency for intervention. Thus, observing blunting of the costophrenic angle is a clear signal that action may be needed to address the excess fluid in the pleural space.