Sometimes referred to as “water on the lungs,” a pleural effusion is the accumulation of excess fluid between the layers of the pleura, which are thin membranes lining the lungs and the inside of the chest cavity. These membranes serve to lubricate and facilitate breathing. With a pleural effusion, fluid builds up in the space between these pleural layers.

A pleural effusion occurs when fluid collects between the parietal and visceral pleural surfaces within the thorax. A thin layer of fluid is always present in this space to provide lubrication and allow for easy movement of the lung during inspiration and expiration. If the normal balance of fluid production and removal is disrupted, leading to either too much fluid being produced or not enough being cleared, fluid accumulates, resulting in a pleural effusion.

Types

Healthcare providers may use the terms “transudative” and “exudative” to describe the two primary categories of pleural effusions.

• Transudative: The fluid in this type of pleural effusion is similar in composition to the fluid normally found in the pleural space. It forms from liquid leaking across healthy pleura. This type rarely requires drainage unless the volume is very large. Congestive heart failure is the most common cause of transudative effusions.

• Exudative: This type forms from additional liquid, protein, blood, inflammatory cells, or sometimes bacteria that leak across damaged blood vessels into the pleura. Drainage may be necessary, depending on the size of the effusion and the extent of inflammation. Common causes include pneumonia and lung cancer.

Causes

A wide array of conditions can lead to a pleural effusion. Some of the more common causes include:

• Leaking from other organs: This often happens in cases of congestive heart failure, where the heart’s ability to pump blood effectively is compromised. It can also stem from liver or kidney disease, where fluid accumulates in the body and subsequently leaks into the pleural space.

• Cancer: Lung cancer is a frequent culprit, but other cancers that have metastasized to the lung or pleura can also cause effusions.

• Infections: Certain illnesses, such as pneumonia or tuberculosis, can result in pleural effusion.

• Autoimmune conditions: Diseases like lupus or rheumatoid arthritis are known causes.

• Pulmonary embolism: This is a blockage in an artery within one of the lungs, which can lead to a pleural effusion.

Symptoms

Some individuals may not experience any symptoms. Symptoms are more likely to manifest when a pleural effusion is moderate to large in size, or if significant inflammation is present.

If symptoms do occur, they may include:

• Shortness of breath

• Chest pain, especially when taking deep breaths (referred to as pleurisy or pleuritic pain)

• Fever

• Cough

• Dyspnoea (difficulty breathing)

• Dullness to percussion (a thudding sound when tapping the chest)

• Quieter breath sounds upon auscultation

Diagnosis

A doctor will discuss the patient’s symptoms and conduct a physical examination. This will involve tapping on the chest and listening with a stethoscope.

To confirm the presence of a pleural effusion, imaging tests are typically required, such as:

• Chest X-ray: Pleural effusions appear white on X-rays, while air spaces look black. If a pleural effusion is suspected, additional X-ray films may be taken with the patient lying on their side to determine if the fluid moves freely within the pleural space.

• Thoracic MRI

• Thoracic CT scan

Treatment

Often, the doctor may only need to address the underlying medical condition that caused the pleural effusion. For example, antibiotics would be prescribed for pneumonia, or diuretics for congestive heart failure.

Large, infected, or inflamed pleural effusions frequently require drainage to alleviate symptoms and prevent further complications.

Procedures for treating pleural effusions include:

• Thoracentesis: A procedure in which a needle is inserted into the pleural space, between the lungs and the chest wall. If the effusion is large, the doctor may withdraw more fluid than needed for testing simply to ease the patient’s symptoms.

• Tube thoracostomy (chest tube): The doctor makes a small incision in the chest wall and inserts a plastic tube into the pleural space, which remains in place for several days.

• Pleural drain: If pleural effusions recur frequently, the doctor may implant a long-term catheter through the skin into the pleural space. This allows the patient to drain the pleural effusion at home, with guidance from their doctor on how and when to perform the drainage.

RISK FACTORS FOR PLEURAL EFFUSION

• Congestive Heart Failure (CHF)

• Pneumonia

• Malignancy (cancer)

• Pulmonary embolism