 A thoracocentesis (pleural tap) is often performed here while a patient is in full expiration because of less risk of puncturing the lungs and thereby causing pneumothorax.In anatomy, the costophrenic angles are the places where the diaphragm ("-phrenic") meets the ribs ("costo-").Each costophrenic angle can normally be seen as on chest x-ray as a sharply-pointed, downward indentation (dark) between each hemi-diaphragm (white) and the adjacent chest wall (white).