What is costophrenic angles in a chest x-ray mean?

Costophrenic angles are the corners formed where the diaphragm meets the rib cage in a chest X-ray. They are important anatomical landmarks used to assess for fluid accumulation, such as pleural effusion, which can cause blunting of these angles. A normal costophrenic angle is sharp and well-defined, while blunting or obscuration may indicate pathology. Evaluating these angles helps in diagnosing various respiratory and cardiac conditions.