Chylothorax

What is chylothorax?

Chylothorax is a rare, potentially life-threatening condition caused by a build-up of milky white fatty lymphatic fluid (chyle) in the chest. The chyle leaks from the thoracic ducts (the primary lymphatic vessels that carry chyle) into the chest. It is an irritant that can cause inflammation of the surface of the lungs and heart. The fluid build-up can also put pressure on organs and keep the lungs from inflating properly.

Anything that disrupts the normal flow of chyle from the thoracic duct can cause chylothorax. This can include trauma, abnormalities of the lymphatic vessels, heart disease, fungal infection, heartworm infection, abnormal positioning of organs, abnormal tissue growth (neoplasia), and abnormalities of the thoracic duct that are present from birth (congenital). However, in many cases, the underlying cause cannot be identified and the diagnosis is idiopathic chylothorax, or chylothorax of unknown origin.

Chylothorax can occur in any dog or cat breed. Males and females appear to be equally affected.

What are the clinical signs of chylothorax?

The clinical signs of chylothorax are often similar to those seen with other respiratory illnesses. These can include difficulty breathing, coughing, lethargy, exercise intolerance, and loss of appetite (which can lead to weight loss over time).

How is chylothorax diagnosed?

Diagnosis of chylothorax is based on patient history, chest and lung sounds (as evaluated with a stethoscope), and diagnostic testing. These tests may include may include chest x-rays, ultrasound, and/or computed tomography (CT), heartworm testing, and echocardiography. Analysis of fluid from the chest cavity can be used to determine if the fluid is chyle. In particular, detection of high triglyceride (fat) levels, and identification of large numbers of small lymphocytes (a type of white blood cell) indicate the presence of chyle. Further diagnostics may be performed to look for the underlying cause.

How is chylothorax treated?

The first treatment for chylothorax is often drainage of the fluid from the chest (thoracocentesis) to stabilize the patient. Fluid usually reforms within days to weeks. A drain may be placed in the chest to facilitate fluid removal. Fluid removal does not address the underlying cause and is unlikely to resolve the condition.

Specific diets, medications, and supplements may be used to reduce fluid accumulation on a case-by-case basis. Medical management of chylothorax depends on controlling the underlying condition. However, since the underlying cause is unknown in many cases, specific therapy is often not possible and generally unsuccessful.

Surgery to close the leaking thoracic ducts is the only permanent solution for chylothorax and may be recommended if the condition persists despite medical therapy. The most common procedure, thoracic duct ligation (TDL), is often performed as an open surgery, but UC Davis offers an alternative minimally invasive approach, and causes less discomfort, but has a similar success rate and quicker recovery. A special medical dye is injected into the lymph nodes and travels through the thoracic ducts. Intraoperative near-infrared imaging illuminates the dye, making the normally tiny ducts that can be very difficult to see, more visible for the procedure.

In some cases, TDL is combined with additional surgical procedures to improve the success rate and avoid side effects.

Ports or shunts may be implanted to move chyle to improve patient comfort and alleviate respiratory issues. However, owners must either manually manipulate the pump to move the fluid or aspirate the fluid directly, depending on the device used.

What is the prognosis for chylothorax?

The prognosis for animals with chylothorax varies depending on a number of factors. These include the ability to stabilize breathing, identification and treatment of the underlying cause and the ability of the surgical team to identify all of the ducts at surgery and ligate them. Since chyle is an irritant, prolonged exposure can form scar tissue around the lungs and heart, creating additional issues.

Medical and surgical treatments have varying success rates. Conservative (medical) treatment is rarely successful, and surgery is often necessary. The most common complication is persistent fluid in the chest, and recurrence of fluid accumulation has been reported up to five years after surgery. However, more than 90% of dogs and 60% of cats experience successful resolution, with an approximately 5-10% recurrence rate at a later time.

How can chylothorax be prevented?

Since the underlying cause is often unknown, it is difficult to prevent chylothorax. Heartworm disease can cause chylothorax in some cases, so it is important to discuss the prevention of this condition with your veterinarian.

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