chylothorax

After a fatty meal, the gut sends absorbed fat not into the bloodstream first but into the lymph system, as a milky fluid called chyle that travels up a large lymph channel in the chest. A chylothorax is what happens when that pipe leaks: the creamy, fat-laden fluid spills into the pleural space.

The main culprit is damage to the thoracic duct, the body's largest lymph vessel, which runs up through the chest. It can be torn during chest or heart surgery, blocked or eroded by a tumor (lymphoma is a classic cause), or disrupted by trauma or rare lymphatic diseases. Because chyle is rich in fat, protein, antibodies and immune cells, losing a lot of it over time drains nutrition and weakens immunity.

The fluid is typically milky and confirmed by finding high levels of a fat called triglyceride or by detecting chylomicrons. Treatment aims to slow the leak and let it heal — often a very low-fat diet or feeding that bypasses the gut, sometimes drainage — while persistent or high-volume leaks may need a procedure to plug the duct or surgery.