Like pulmonary hypertension are plural diseases most commonly secondary complications of underlying pulmonary diseases, and not a primary disease itself.
Pleural effusion and pleuritis
Pleural effusion is the abnormal presence of fluid in the pleural space. The fluid can either be transudate or exudate. If it is transudate is it called hydrothorax.
Hydrothorax is most frequently caused by increased capillary hydrostatic pressure in the pleural vessels due to congestive heart failure or any disease that causes hypoproteinaemia, like liver disease or nephrotic syndrome. Transudates are often reabsorbed if the cause is solved.
Pleural exudate can be serous, fibrinous, haemorrhagic or purulent (suppurative). Pus accumulation in the pleural cavity is also called pleural empyema. Pleural exudate is commonly caused by one of these processes:
- Bacterial pleuritis that has spread from the lungs or with blood
- Lung infarct
- Viral pleuritis
- Rheumatoid arthritis
Cancer-related pleural exudate is often due to lung cancer, mesothelioma or metastatic breast cancer. They’re often large and haemorrhagic and contain cancer and inflammatory cells.
Fibrinous, haemorrhagic and purulent exudates may lead to fibrinous organization, which can cause adhesions and fibrous thickening of the pleura.
Pneumothorax, haemothorax, chylothorax and pleural empyema
Pneumothorax refers to the presence of air or any other gas in the pleural space. It may happen spontaneously or secondary to emphysema, lung abscess or a fractured rib. Secondary pneumothorax occurs when there is a rupture of the lung close to the pleural surface that allows inhaled air to enter the pleural cavity.
The pressure in the pleural cavity is normally negative to allow the lungs to expand in it. When it suddenly becomes filled with air will the pressure be equal with atmospheric pressure. This high pressure causes the lung to collapse.
Haemothorax is the collection of blood (and not bloody exudate) in the pleural cavity. It’s associated with ruptured intrathoracic aortic aneurysm. It’s almost always fatal.
Chylothorax is the collection of lymphatic fluid in the pleural cavity. The lymphatic fluid contains lipids, so it’s milky in appearance. It occurs due to obstruction of major lymphatic ducts, most commonly due to cancer.
Pleural empyema is usually a complication of pneumonia or lung abscess
Mesothelioma is a cancer of mesothelial cells that usually occurs in the parietal or visceral pleura but can also arise from the peritoneum and pericardium. The biggest risk factor is asbestos exposure, but it takes 25-40 years from the initial exposure until the cancer develops. Cigarette smoking further increases the risk.
Asbestos are mineral fibres, not particles, so they’re impossible for macrophages to get rid of. They remain in the lung for life. The cancer itself is usually preceded by extensive pleural fibrosis. Asbestos fibres generate reactive oxygen species, which cause DNA damage leading to cancer. p16, p53, RB and NF2 mutation is seen in many mesotheliomas.
Mesotheliomas rarely metastasize to distant locations, but they do invade the thoracic wall and subpleural lung parenchyme. The only effective treatment in removal of the affected lung and pleura.
Mediastinitis and thymoma
Mediastinitis can be a severe condition. It’s commonly caused by thoracic surgery, and can be either acute or chronic granulomatous.
Thymomas are thymic epithelial tumors. They can be benign or malignant, but both types are rare. Common complications include
- Superior vena cava syndrome
- Myasthenia gravis
82. Lung tumors