Pleural effusion

Definition

The term "pleural effusion", extracted from the medical language, refers to an excessive accumulation of fluid inside the pleural cavity. Under physiological conditions, the pleural cavity contains no more than 10-20 ml of liquid; pleural effusion is an expression of inadequate disposal or exaggerated production of this pleural fluid. Before proceeding with the analysis of the condition, let's clarify some concepts, useful to better understand the distinctive features of the pathology.

Terminology

PLEURA: thin layer of connective tissue with support function and lining of the lungs. The pleura is a serous membrane consisting of two sheets: the visceral pleura is the innermost leaflet which adheres to the external pulmonary wall, while the parietal pleura covers the thoracic cavity (from the inside) and the upper face of the diaphragm

PLEURIC CABLE: very thin virtual space interposed between the visceral pleura and the parietal pleura

PLEURIC LIQUID: enclosed in the pleural cavity, it has a lower pressure than the ambient one. A right amount of liquid is essential to ensure the sliding of the two pleural membranes, while ensuring their union. In physiological conditions, the presence of pleural fluid prevents collapse of the lung (collapse is a typical event of pneumothorax)

Statistics and Causes

The pleural effusion may be a lighted sign of a condition affecting the pleura, the lung or extrapulmonary lesions.

Pleural effusion is a pathological condition that is common to most forms of pleuritis (inflammation of the pleura).

The presence of a malignant pleural effusion may constitute a complication of several cancers: in the USA, for example, the average annual incidence is 150, 000 patients. Medical statistics show that the pleural effusion occurs in 7-15% of patients affected by primary lung cancer. Breast cancer, lymphoma and thoracic neoplasms can also predispose the patient to pleural effusion.

Together with the empyema (collection of purulent fluid inside the pleural cavity) and the pulmonary abscess, pleural effusion is often found in numerous clinical pathologies that increase mortality.

Pleural effusion may also depend on virus-borne infections, particularly Herpes zoster, Morbillivirus, Paramyxovirus and Orthomyxovirus (influenza and parainfluenza viruses).

Classification

It is important to distinguish two main types of pleural effusion: exudate and transudate. Let us briefly recall that even blood, pus or kilo can accumulate in the pleural space.

TRANSUDATIVE Pleural effusion: occurs in case of rupture of the hydrostatic * and oncotic forces **, operating through the pleural and capillary membranes. In the presence of transudate, the pleurae are healthy. The transudative pleural effusion may result to:
- Cirrhosis
- Peritoneal dialysis
- hypoalbuminemia
- Left ventricular failure
- Pulmonary embolism, hypothyroidism, mitral stenosis (less frequently)
ESSENTIAL Pleural effusion: typical expression of an infectious-inflammatory process, the exudate is formed in case of greater permeability of the pleural surface and / or of the capillaries. Exudative pleural effusion can be favored by:
- Lung cancer and breast cancer (often)
- Pneumonia (very frequent)
- Rheumatoid arthritis, exposure to asbestos, pancreatitis, tuberculosis (less frequently)
- Fungal infections (rare)

Terminology:

* Hydrostatic pressure: force exerted by the fluid on the surfaces with which it is placed in contact. An increase in hydrostatic pressure, common in the presence of hypertension, favors the accumulation of pleural fluid through increased filtration.

** Oncotic pressure: osmotic pressure exerted by proteins dispersed in solution in plasma. The oncotic pressure is therefore heavily influenced by the concentration of proteins in biological liquids: when this decreases, the oncotic pressure also decreases and the pleural fluid increases due to the reduction of its reabsorption.

How it forms

The pleural effusion may be due to an exaggerated increase in the hydrostatic pressure and permeability of the capillaries, to a decrease in the oncotic blood pressure, to the reduction of pressure in the pleural space, and to a marked inefficiency of lymphatic drainage.

Pleural effusion:

↑↑ hydrostatic pressure and capillary permeability → typical of heart failure and inflammation

↓↓ plasma oncotic pressure → typical of hypoalbuminemia, nephrosis syndrome, liver cirrhosis

↓↓ pressure in the pleural space → retraction of the lung

Malfunction of lymphatic drainage → typical of neoplasia and fibrosis

Fluid transfer from the peritoneal space to the pleural cavity → ascites

As a typical consequence of ascitic effusions (collection of fluid in the peritoneal cavity), pleural effusion can also be favored by the passage of fluid from the peritoneum.