A chylothorax is an abnormal accumulation of chyle, a type of lipid-rich lymph, in the pleural space surrounding the lung.

The lymphatic vessels of the digestive system normally return lipids absorbed from the small bowel via the thoracic duct, which ascends behind the esophagus to drain into the left brachiocephalic vein.

If normal thoracic duct drainage is disrupted, either due to obstruction or rupture, chyle can leak and accumulate within the negative-pressured pleural space.

In people on a normal diet, this fluid collection can sometimes be identified by its turbid, milky white appearance, since chyle contains emulsified triglycerides.

[2] It is important to distinguish a chylothorax from a pseudochylothorax (a pleural effusion that happens to be high in cholesterol), which has a similar appearance visually but is caused by more chronic inflammatory processes and requires a different treatment.

A large chylothorax may lead to breathlessness or a feeling of pressure in the chest, caused by fluid restricting the expansion of the lungs, although large chylothoraces may remain asymptomatic if the chylothorax has accumulated slowly, as the lungs may have had time to become used to the pressure.

[1] Large chylothoraces may cause signs related to the loss of nutrients, including features of malnutrition or decreased ability to fight infections.

Historically the most common form of chylothorax was non-traumatic, but traumatic chylothoraces now represent the majority of cases, with most arising as postoperative complications of surgery.

Other operations like mediastinal tumor resection, thoracic aneurysm repair, sympathectomy, and any other surgeries that take place in the lower neck or the mediastinum can lead to chylothorax.

Chylotharax after trauma but not after surgery has also been described after central line placement, pacemaker implantation, and embolization of a pulmonary arteriovenous malformation.

[5] For example, placement of a central venous catheter can potentially disrupt drainage of lymph into the subclavian veins, followed by the thoracic duct, resulting in chylothorax.

In the case of mediastinal lymphadenopathy, the enlarged lymph node causes compression of the lymphatic channels and thoracic duct.

This impedes the centripetal drainage of the flow of lymph from the edges of the lung parenchyma and pleural surfaces.

In the case of yellow nail syndrome, or lymphedema, chylothorax is caused by hypoplasia or dilation of the lymph vessels.

In rare cases, like in hepatic chylothorax, chylous ascites crosses the diaphragm into the pleural cavity.

However, neither a normal chest x-ray nor an ultrasound can differentiate a chylothorax from any other type of pleural effusion.

[1] Another, more commonly used type of lymphogram is nuclear lymphoscintigraphy; this procedure requires human pentetic acid labeled Tc99m to be injected into the subcutaneous lesions of both sides of the dorsum of the foot.

Chylothoraces are typically exudative and often contain a high number of lymphocytes and have low levels of the enzyme lactate dehydrogenase (LDH).

[1] Those with large chylothoraces may need nutritional support due to the nutrients lost, primarily to correct protein and electrolyte losses.

[13] Another treatment option is pleuroperitoneal shunting (creating a communication channel between the pleural space and peritoneal cavity).

Since surgery to close the leak is not reliable, talc pleurodesis is recommended; in a case study of 19 people with refractory malignant chylothorax due to lymphoma, it resulted in success for all affected individuals.

[5] Chemical pleurodesis is an option, since the leaking of lymphatic fluids is stopped by irritating the lungs and chest wall, resulting in a sterile inflammation.

This causes the lung and the chest wall to fuse together, thus preventing lymphatic fluids from leaking into the pleural space.