Pleural cavity

In anatomy, the pleural cavity is the potential space between the lungs and the chest wall[?]. It has virtually nothing in it in the normal non-diseased state, except a small amount of pleural fluid[?]. The cavity is lined by specialized epithelium[?] called pleura. The pleura that borders the chest wall is called the parietal pleura and is highly sensitive to pain. The pleura that borders the lung and other visceral tissues[?] is called the visceral pleura, is not sensitive to pain and has a dual blood supply, from the bronchial and pulmonary arteries. There is no anatomical connection between the left and right pleural cavities, as they are separated by the mediastinum[?].

The pleura and pleural fluid function to preserve a vacuum state that enables breathing. This function of the pleural cavity can be disrupted in several ways:

Pneumothorax[?] - when a pleural cavity communicates with the atmosphere or the airspace within the lungs, air can accumulate in the pleural cavity, causing the lung on the same side to collapse. If a piece of tissue forms a one-way valve that allows air to penetrate into the pleural cavity but not to escape, overpressure can build up on the pneumothorax (tension pneumothorax[?]). This may lead to severe shortness of breath as well as circulatory collapse, both life-threatening conditions. Common causes of pneumothorax are trauma, atmospheric overpressure, and preexisting lung disease; a pneumothorax may also occur spontaneously without apparent cause.

Small pneumothoraces often resolve spontaneously and may require no other treatment than clinical observation. A large pneumothorax or tension pneumothorax can be a medical emergency. It is usually treated using a chest drainage: a tube is inserted through the chest wall and suction applied to evacuate air from the pleural cavity, thus allowing the lung to expand again.

Pleural effusion[?] - fluid can accumulate in the pleural space, compressing the lungs. This can occur as a consequence of reasons such as:

• malignancy
• infection
• autoimmune disease such as lupus erythematosus
• heart failure
• bleeding, often due to chest trauma (hemothorax[?])
• low oncotic pressure of the blood plasma
• lymphatic obstruction
• accidental infusion of fluids

Congestive heart failure, bacterial pneumonia and malignancy constitute the vast majority of causes in the developed countries, although tuberculosis is a common cause in the developing world.

In states of excess accumulation, pleural fluid can be sampled and evaluated to determine what disease state may be causing it. The evaluation consists of

1. Gram stain and culture - identifies bacterial infections
2. cell count and differential - differentiates exudative from transudative effusions
3. cytology - identifies cancer cells, may also identify some infective organisms
4. chemical composition including protein, lactate dehydrogenase[?], amylase, pH and glucose - differentiates exudative from transudative effusions
5. other tests as suggested by the clinical situation - lipids, fungal culture, viral culture, specific immunoglobulins