Final answer:
To spot a pleural effusion on a chest x-ray, look at the lung bases for blunting of the costophrenic angles, horizontal fluid levels, or diffuse haziness, which will vary depending on the patient's position during the x-ray.
Step-by-step explanation:
When looking for a pleural effusion on a chest x-ray, you typically examine the areas where the fluid is likely to collect due to gravity. In an upright patient, pleural effusion will appear on the x-ray at the lung bases, often causing blunting or obscuration of the costophrenic angles. The effusion may layer out as a horizontal fluid level if large enough, or it may produce a more diffuse haziness in the affected area, especially if the patient is lying down. If a patient is lying down during the x-ray, such as in a supine position, fluid can collect along the posterior chest wall, leading to a different appearance known as a 'supine effusion.' With a sizeable pleural effusion, the lung may also appear compressed, and there could be a shift of the mediastinum to the opposite side if the effusion is significant.