An Overview of Chylothorax

A chylothorax is a type of pleural effusion (a collection of fluid between the membranes lining the lungs called the pleura), but instead of normal pleural fluid, it's a collection of chyle (lymph fluid). It is caused by a blockage or disruption of the thoracic duct in the chest. Causes include trauma, chest surgeries, and cancers involving the chest (such as lymphomas).

It may be suspected in studies such as a chest X-ray, but the diagnosis is usually made by inserting a needle into the pleural cavity (thoracentesis) and removing fluid. A number of different treatment options are available. Sometimes they go away on their own or with medication, but often they require procedures such as shunt placement, thoracic duct ligation, embolization, and others.

Chylothorax is uncommon in both adults and children but is the most common form of pleural effusion in newborns.

Anatomy and Function

The thoracic duct is the main lymph vessel in the body, with lymphatic vessels being the part of the immune system that carries lymph throughout the body. The thoracic duct serves to carry chyle from the intestines to the blood.

Components of Chyle

Chyle consists of chylomicrons (long-chain fatty acids and cholesterol esters) as well as immune cells and proteins such as T lymphocytes and immunoglobulins (antibodies), electrolytes, many proteins, and fat-soluble vitamins (A, D, E, and K). As the thoracic duct passes through the chest, it also picks up lymph from lymphatic vessels that drain the chest.

A large amount of fluid (roughly 2.4 liters in an adult) passes through this duct every day (and can end up in the pleural cavity with a chylothorax).

Thoracic Duct Obstruction

The duct can be directly injured via trauma or surgery, or blocked by tumors (see causes below). When the thoracic duct is blocked (such as by a tumor), it usually leads to secondary rupture of lymphatic ducts leading to the blockage.

Due to the location of the thoracic ducts, pleural effusions are more common on the right side of the chest, though at times they are bilateral.

Many people are familiar with the lymphedema with breast cancer that some women experience after breast surgery that leads to swelling and tenderness of the arm. In this case, the accumulation of lymph fluid in the arm is responsible for the symptoms. With a chylothorax, the mechanism is similar, with a chylothorax being a form of obstructive lymphedema with the accumulation of lymph fluid between the membranes lining the lungs, rather than the arm.

Symptoms

Early on, a chylothorax may have few symptoms. As fluid accumulates, shortness of breath is usually the most common symptom. As the effusion grows, people may also develop a cough and chest pain. A fever is usually absent.

When a chylothorax occurs due to trauma or surgery, symptoms usually begin about a week after the accident or procedure.

Causes

There are a number of possible causes of a chylothorax, with the mechanism being different depending on the cause.

Tumors

Tumors and/or enlarged lymph nodes (due to the spread of tumors) in the mediastinum (the area of the chest between the lungs) are a common cause, responsible for around half of these effusions in adults. The chylothorax develops when a tumor infiltrates the lymphatic vessels and thoracic duct.

Lymphoma is the most common cancer to cause a chylothorax, especially non-Hodgkin's lymphomas. Other cancers that may lead to chylothorax include lung cancer, chronic lymphocytic leukemia, and esophageal cancer. Cancers that spread (metastasize) to the chest and mediastinum, such as breast cancer, may also cause a chylothorax.

Surgery

Chest surgery (cardiothoracic) is also a common cause of a chylothorax and is the most common cause in children (often due to surgery for congenital heart disease). It usually occurs due to direct damage to the thoracic duct during the operation.

Trauma

Trauma is another common cause of a chylothorax, and often results from blunt trauma, blasting injuries, gunshots, or stabbings. On rare occasion, a chylothorax has occurred from coughing or sneezing alone.

Congenital Syndromes and Developmental Abnormalities

A congenital (from birth) chylothorax may be seen with congenital lymphangiomatosis, lymphangiectasis, and other lymphatic abnormalities. It may also occur in association with syndromes such as Down syndrome, Turner's syndrome, Noonan syndrome, and Gorham-Stout syndrome.

Diagnosis

The diagnosis of a chylothorax may be suspected based on recent chest surgery or trauma. On exam, decreased lung sounds may be heard.

Imaging

Imaging tests are usually the first steps in diagnosis and may include:

• Chest X-ray: A chest X-ray may show the pleural effusion, but can't distinguish between a chylothorax and other types of pleural effusions.
• Ultrasound: Like a chest X-ray, ultrasound may suggest a pleural effusion, but can't distinguish a chylothorax from other effusions.
• Chest CT: If a person develops a chylothorax without trauma or surgery, a chest CT is usually done to look for the presence of a tumor or lymph nodes in the mediastinum. On occasion, the damage to the thoracic duct may be seen.
• MRI: While an MRI is good for visualizing the thoracic duct, it isn't often used in the diagnosis. It may be helpful for those who have allergies to the contrast dye used with CT, and when better visualization of the thoracic duct is needed.

Procedures

Procedures may be used to obtain a sample of the fluid in a chylothorax or to determine the type and extent of damage to the thoracic duct or other lymphatic vessels.

Lymphangiography: A lymphangiogram is a study in which a dye is injected in order to visualize the lymphatic vessels. It may be done to help diagnosis the extent of damage (and location) to the lymphatic vessels, and also in preparation for embolization procedures (see below).

Newer procedures such as dynamic contrast magnetic resonance lymphangiography and intranodal lymphangiography combine this procedure with radiological testing to better detect the source of the leak.

Lymphoscintigraphy: Unlike a lymphangiogram, lymphoscintigraphy uses radioactive markers to visualize the lymphatic system. After injecting a radioactive tracer, a gamma camera is used to detect the radiation and indirectly visualize the lymphatic vessels.

Thoracentesis: A thoracentesis is a procedure in which a long fine needle is inserted through the skin on the chest and into the pleural cavity. Fluid can then be withdrawn to be evaluated in the lab. With a chylothorax, the fluid is usually milky-appearing and has a high triglyceride level. It is white due to emulsified fats in lymphatic fluid, and when allowed to sit the fluid separates (like cream) into layers.

Differential Diagnosis

Conditions that may appear similar to a chylothorax, at least initially include:

• Pseudochylothorax: A pseudochylothorax differs from a chylothorax as it involves an accumulation of cholesterol in a pre-existing effusion rather than lymph fluid/triglycerides in the pleural space, and has different causes and treatments. A pseudochylothorax may be associated with pleural effusions due to rheumatoid arthritis, tuberculosis, or an empyema.
• Malignant pleural effusion: In a malignant pleural effusion, cancer cells are present within the pleural effusion.
• Hemothorax: In a hemothorax, blood is present in the pleural cavity.

All of these conditions can appear similar on imaging tests such as a chest X-ray, but will differ when fluid obtained from a thoracentesis is evaluated in the lab and under the microscope.

Treatments

With a small chylothorax, the effusion can sometimes be treated conservatively (or with medications), but if symptomatic, it often requires a surgical procedure. The choice of treatment often depends on the underlying cause. The goal of treatment is to remove the fluid from the pleural cavity, keep it from reaccumulating, treat any problems due to the chylothorax (such as nutritional or immune problems), and treat the underlying cause. Some thoracic duct leaks resolve on their own.

For some people, surgery should be considered much sooner, such as those who develop a chylothorax after surgery for esophageal cancer, if the leak is large, or if severe immune, electrolyte, or nutrition problems develop.

Unlike some pleural effusions in which a chest tube is placed to continually drain the effusion, this treatment is not used with a chylothorax as it can result in malnutrition and problems with immune function.

Medications

The medications somatostatin or octreotide (a somatostatin analogue) may reduce the accumulation of chyle for some people, and may be a non-surgical option, especially those who have a chylothorax as a result of chest surgery.

Other medications are being evaluated in research, such as the use of etilefrine, with some success.

Surgery

A number of different procedures may be done to stop the accumulation of fluid in a chylothorax, and the choice of technique usually depends on the cause.

• Thoracic duct ligation: Thoracic duct ligation involves ligating (cutting) the duct to prevent flow through the vessel. This has conventionally been done via a thoracotomy (open chest surgery) but may be done as a less invasive video-assisted thoracoscopic surgery (VATS) procedure.
• Shunting: When fluid continues to accumulate, a shunt (pleuroperitoneal shunt) may be placed that carries the fluid from the pleural cavity into the abdomen. By returning the fluid to the body, this type of shunt prevents the malnutrition and other problems that could occur if the lymph were to be removed from the body. A pleuroperitoneal shunt may be left in place for a significant period of time.
• Pleurodesis: A pleurodesis is a procedure in which a chemical (usually talc) is injected into the pleural cavity. This creates inflammation that causes the two membranes to stick together and prevent further accumulation of fluid in the cavity.
• Pleurectomy: A pleurectomy is not often done, but involves removing the pleural membranes so that a cavity no longer exists for fluid to accumulate.
• Embolization: Either thoracic duct embolization or selective duct embolization may be used to seal the thoracic duct or other lymphatic vessels shut. The advantages of embolization are that the leak can be visualized directly and it is a less invasive procedure than some of the above.

Dietary Changes

People with a chylothorax recommended to reduce the amount of fat in their diets and the diet may be supplemented with medium chain fatty acids. Total parenteral nutrition (giving proteins, carbohydrates, and fats intravenously) may be needed to maintain nutrition. Conventional intravenous fluids only contain saline and glucose.

Supportive Care

A chylothorax can lead to problems with nutrition and immunodeficiency, and careful management of these concerns is needed.

Coping and Prognosis

A chylothorax can be frightening as an adult or as a parent if it is your child, and confusing as it is seldom talked about. The prognosis often depends on the underlying process, but with treatment, it is often good. That said, it can lead to a number of problems such as nutritional deficiencies, immune deficiencies, and electrolyte abnormalities that will need to be closely monitored and treated. Being an active member of your medical team can be very helpful to make sure all of these concerns are carefully addressed.

Long-term studies published in 2012 found that children who experience a chylothorax as an infant tend to do very well, without significant developmental delays or problems with lung function.