Picture of Pleural Effusion
Pleural effusion is a condition in which fluid builds up between the membranes (parietal pleurae and visceral pleurae) that line the lungs and the chest cavity. The visceral pleura envelops the lungs. The parietal pleura is the lining of the inner chest wall. About 3 to 4 teaspoons of fluid is normally present between the two types of membranes. It acts as a lubricant. If the quantity of pleural fluid increases significantly, it is known as a pleural effusion.
Chest pain and difficulty breathing (dyspnea) are the most commonly reported symptoms by patients with pleural effusion. Many cases of the condition are asymptomatic and discovered during routine physical examinations or chest X-rays. X-ray is often used to confirm the diagnosis.
Text Reference: American Family Physician, vol. 90, 2014: "Diagnostic Approach to Pleural Effusion"