Pleural effusion: what it is, what causes it and how to prevent it

By Cristiano Antonino On Nov 24, 2022

Pleural effusion is a clinical condition characterised by excessive accumulation of fluid within the pleural cavity

The pleural cavity is a very thin space between the visceral pleura (the serous membrane that adheres to the outer lung wall and thus interposes itself between the organs of the mediastinum and the lungs internally) and the parietal pleura (the serous membrane that lines the thoracic cavity from the inside and the upper face of the diaphragm, thus interposing itself between the osteo-muscular thoracic wall and the lungs externally).

What is pleural effusion?

The pleural fluid between the visceral and parietal pleura allows these two membranes to slide over each other during respiratory acts and prevents the lung from collapsing (under physiological conditions, the pressure inside the pleural fluid is lower than the ambient pressure precisely to prevent this condition from occurring).

Pleural effusion represents inadequate disposal (exudate pleural effusion) or excessive production (exudate pleural effusion) of this fluid.

The effusion may be unilateral or bilateral; it may occupy the large pleural cavity or be localised in a circumscribed part of the pleural space.

What are the causes of pleural effusion?

There are several causes of pleural effusion.

There are two types of pleural effusion that can develop: transudate-type pleural effusions – or ‘exudates’ – and exudate-type pleural effusions – or ‘exudates’.

The exudate-type pleural effusion forms due to altered factors (hydrostatic and oncotic forces) that influence the formation or reabsorption of pleural fluid (pleuras in the presence of exudate-type effusion are healthy).

These include:

hyperhydration,
pulmonary venous hypertension
systemic venous hypertension
liver cirrhosis
nephrotic syndrome

Pleural effusions of the exudate type are an expression of infectious-inflammatory processes.

They arise due to the alteration of the mechanisms responsible for the filtration and reabsorption of pleural fluid.

Causes that may be at the origin of these include:

infectious or inflammatory processes affecting the lung
pulmonary embolism
acute pancreatitis
neoplasms
rheumatoid arthritis
syndrome following cardiac injury
fungal pleurisy
subdiaphragmatic abscess
exposure to asbestos

What are the symptoms of pleural effusion?

The symptoms that characterise pleural effusion vary depending on the amount of fluid present in the pleural cavity and the rate at which it accumulates.

Among the most frequent symptoms are: