Pleural Effusion in Cats

What is pleural effusion?

Pleural effusion is the abnormal accumulation of fluid in the chest cavity. Fluid accumulates in the pleural sac, not the lungs, so the lungs are essentially floating in a chest full of fluid. This fluid occupies space within the chest, so the lungs cannot expand as fully as they should.

What causes pleural effusion?

Pleural effusion can have several causes. The most common causes in cats include the following:

Pyothorax. This term refers to pus in the chest cavity. A pyothorax forms in response to a severe bacterial infection in the chest cavity due to a blood-borne infection or a penetrating chest wound.

Chylothorax. This term refers to the accumulation of lymphatic fluid within the chest cavity. Chylothorax occurs when lymphatic fluid (chyle) leaks into the pleural space from a lymphatic duct that runs within the chest. Possible causes of chylothorax include trauma and increased pressure on the duct (due to heart disease or other conditions). Many cases are idiopathic, meaning that no cause can be identified.

Heart failure. When cats experience heart failure, the heart can no longer pump fluid throughout the body as it is intended to do, which can cause accumulation of excess fluid around the lungs.

Cancer. Tumors in the lungs or chest wall can lead to pleural effusion.

Feline infectious peritonitis (FIP). This syndrome is caused by a mutated form of a feline coronavirus. In some cats, infection with mutated coronavirus can lead to blood vessel damage, which results in fluid leakage. When FIP affects the chest cavity, pleural effusion results.

Diaphragmatic hernia. A diaphragmatic hernia refers to a defect in the diaphragm that allows abdominal organs to enter the chest cavity. A diaphragmatic hernia can be a birth defect or can be caused by trauma. The presence of abdominal organs in the chest leads to the production of fluid, resulting in pleural effusion.

Lung lobe torsion. Lung lobe torsion occurs when a lobe of the lung twists on itself, cutting off the flow of blood and oxygen to the lung. Lung lobe torsion is often associated with trauma, cancer, or chylothorax, but can also occur spontaneously, with no identifiable cause.

Hemorrhage. Bleeding within the chest cavity may occur due to trauma but can also be associated with blood clotting disorders or the ingestion of anticoagulant rodenticides (rat poison).

Your veterinarian will perform diagnostic tests to determine the most likely cause of your cat’s pleural effusion.

What are the clinical signs of pleural effusion?

Pleural effusion decreases the amount of space available for the lungs to expand within the chest cavity. Therefore, the signs of pleural effusion are related to the fact that affected cats must work harder to breathe.

Cats with pleural effusion often have rapid, shallow breathing. In some cases, you may notice increased respiratory effort – your cat’s abdomen may move significantly with each effort to draw breath. Cats may develop open-mouthed breathing in an effort to increase airflow. Some affected cats may also cough.

Over time, cats may develop additional signs related to their respiratory difficulties. Lethargy, weight loss, and decreased appetite may occur as your cat feels increasingly ill from decreased oxygen intake.

How is pleural effusion diagnosed?

On physical examination, your veterinarian may notice signs that suggest pleural effusion, including pale or blue discolored gums, labored breathing, and an increased respiratory rate. When your veterinarian uses a stethoscope to listen to your cat’s chest, the heart and lung sounds may be muffled by the presence of fluid in the chest.

Pleural effusion is typically diagnosed by taking radiographs (X-rays) of the chest. There are several characteristic findings on radiographs that help your veterinarian identify the presence of pleural effusion. In some cases, ultrasound may also be used to identify pleural effusion. Ultrasound is particularly effective when only small volumes of pleural effusion are present.

Thoracocentesis is typically used to diagnose the cause of the pleural effusion. In this procedure, your veterinarian will use a sterile needle to remove fluid directly from the chest cavity. Removing this fluid often provides immediate relief of some of the breathing difficulties associated with pleural effusion, while also providing a fluid sample that can be used for testing. The chemical parameters of the pleural fluid will be assessed and the fluid will be examined under a microscope for the presence of abnormal cells. Tests performed on the pleural fluid can help your veterinarian diagnose the cause of your cat’s pleural effusion and develop an effective treatment program.

Further testing may be needed to diagnose the underlying cause of your cat’s pleural effusion.

How is pleural effusion treated?

In emergency treatment of pleural effusion, cats are often first placed into an oxygen cage. Cats presenting for pleural effusion often experience shortness of breath and decreased oxygen intake, so an oxygen cage provides some immediate relief and allows your cat to calm down enough for a thorough exam and diagnostics.

In many cases, thoracocentesis is used to remove accumulated fluid. Removing fluid around the lungs allows your cat to breathe more readily. In some cases, a chest tube may be placed to allow repeated fluid drainage, helping your cat breathe more easily.

Once your cat is stabilized, your veterinarian will work to determine the cause of the pleural effusion. Long-term treatment of pleural effusion varies depending on the underlying cause of the effusion.

What is the prognosis?

The prognosis varies depending on the underlying cause of the pleural effusion.