Chylothorax is caused by disruption or obstruction of the thoracic duct or its tributaries that results in leakage of chyle (lymphatic fluid of intestinal origin) into the pleural space. Chylous ascites can also flow into the pleural space. The fluid typically has a high triglyceride content and often a turbid or milky white appearance. In contrast, a cholesterol pleural effusion, which can also have a milky appearance, has a high concentration of cholesterol or lecithin-globulin complexes that accumulate due to pleural inflammation or infection.
Understanding of the anatomy of the thoracic duct, the constituents of chyle, and the diverse etiologies of chylothorax is important to the accurate and efficient diagnosis of chylothorax.
The etiology, clinical presentation, and diagnosis of chylothorax will be reviewed here. The management of chylothorax, the evaluation and management of cholesterol effusions, and general issues regarding the evaluation and treatment of pleural effusions are discussed elsewhere. (See "Management of chylothorax" and "Clinical presentation, diagnosis and management of cholesterol effusions" and "Diagnostic evaluation of a pleural effusion in adults: Initial testing" and "Diagnostic evaluation of pleural effusion in adults: Additional tests for undetermined etiology" and "Imaging of pleural effusions in adults" and "Mechanisms of pleural liquid accumulation in disease".)
CHYLOTHORAX VERSUS CHOLESTEROL EFFUSION
Cholesterol effusions and chylothoraces both classically have a milky or opalescent appearance. However, their etiologies and therapy differ, making it important to distinguish them.
- A chylothorax occurs when lymph fluid accumulates in the pleural space due to disruption or obstruction of the thoracic duct. Chylothoraces contain a high concentration of triglycerides as chylomicrons, unless the patient has no dietary fat ingestion [1-4].
- Cholesterol effusions (also known as a pseudochylothorax or chyliform effusion) are much less common than chylothoraces and contain a high concentration of cholesterol. These effusions typically occur in patients with thickened and sometimes calcified pleural surfaces in the setting of chronic pleural inflammation [5,6]. (See "Clinical presentation, diagnosis and management of cholesterol effusions".)