What is a pleural effusion? how is it treated?

Chest fluid: The pleural space is inside the chest and outside the lung. The space usually has a small amount of natural fluid as lubricant for the lung -visceral pleura to be able to slide over the inner surface of the chest='parietal pleura. Excessive fluid is called an effusion. Other collections can be blood, pus, lymph, chyle. Requires diagnosis, then treated by aspiration, catheter, or tube thoracostomy.

Fluid around lung: Fluid in the pleural space around the lung can come from heart failure, cancer, infection, etc. It is treated by drainage with a needle, insertion of a chest tube, or surgery.