This patient has a large right pleural effusion that is 'sub-pulmonic' in location, meaning that the fluid is beneath the lung, and the lung base is floating on top of it. You can tell this because of the shape of the apparent diaphragm on the right (check labels). Presumably the patient was upright for the PA view, since that is how PA views are done. The left side is normal.

This case demonstrates 'lateralization of the peak' of the right diaphragm, as indicated by the arrow on the label marked 'abnormal contour'. This is a characteristic finding in subpulmonic pleural effusions, which typically do NOT show the expected blunting of the costophrenic angles we usually associate with pleural effusions. On the CT topogram (low resolution digital image done to plan where to image for a CT scan), the patient was supine and the fluid flowed out laterally. Most subpulmonic effusions are NOT loculated, meaning that the fluid collects inferior to the lung only temporarily, and can flow relatively freely into other positions as the patient moves around.