The pleura is a thin, transparent, two-layered membrane that covers the lungs and also lines the inside of the chest wall. The layer that covers the lungs lies in close contact with the layer that lines the chest wall. Between the two thin flexible layers is a small amount of fluid (pleural fluid) that lubricates them as they slide smoothly over one another with each breath. The area containing the fluid is called the pleural space.
In abnormal circumstances, air or excess fluid can get between the pleural surfaces, enlarging the pleural space. If excess fluid accumulates (called pleural effusion Pleural Effusion Pleural effusion is the abnormal accumulation of fluid in the pleural space (the area between the two layers of the thin membrane that covers the lungs). Fluid can accumulate in the pleural... read more ) or if air accumulates (called pneumothorax Pneumothorax A pneumothorax is the presence of air between the two layers of pleura (thin, transparent, two-layered membrane that covers the lungs and also lines the inside of the chest wall), resulting... read more ), one or both lungs may not be able to expand normally with breathing, resulting in the collapse of lung tissue. The pleura can become infected (see Viral Pleuritis Viral Pleuritis Viral pleuritis is a viral infection of the pleura (the thin, transparent, two-layered membrane that covers the lungs), which typically causes chest pain when breathing or coughing. (See also... read more ).
The mediastinum (chest cavity) refers to an area that is bordered by the breastbone (sternum) in front, the spinal column in back, the neck on top, and the diaphragm below. It contains the heart, the thymus gland, some lymph nodes, and parts of the windpipe (trachea), esophagus, aorta, thyroid gland, and parathyroid glands. It does not include the lungs. The mediastinum is divided into three parts:
Mediastinal masses Mediastinal Masses Mediastinal masses include tumors, fluid-filled sacs (cysts), and other abnormalities in the organs of the mediastinum. These organs include the heart, the thymus gland, some lymph nodes, and... read more , abnormal masses such as cysts and tumors, can form in the mediastinum. Mediastinitis Mediastinitis Mediastinitis is inflammation of the mediastinum (the chest cavity, which contains the heart, the thymus gland, some lymph nodes, and parts of the esophagus, aorta, thyroid, and parathyroid... read more may occur when contents from the esophagus leak into the mediastinum, causing irritation and infection. Mediastinitis also may occur after chest surgery (such as those that open the breastbone, for example, median sternotomy). Pneumomediastinum Pneumomediastinum Pneumomediastinum is air in the cavity in the central part of the chest (mediastinum). Air can enter the mediastinum when The small air sacs of the lungs (alveoli) become stretched and torn... read more occurs when air enters the mediastinum.