What is a chylothorax?

What is a Chylothorax?

A chylothorax is the accumulation of chyle (lymphatic fluid) in the pleural space resulting from disruption of the thoracic duct or its tributaries. 1

Definition and Pathophysiology

• Chyle is lymphatic fluid primarily formed in the intestines, composed of proteins, lipids, electrolytes, and lymphocytes. 2
• The hallmark feature is the presence of chylomicrons in the pleural fluid, giving it a characteristic milky, opalescent appearance (though appearance can vary based on nutritional status). 2
• The fluid is odorless, alkaline, and sterile. 2
• Chylothorax typically appears on the right side since most of the thoracic duct is within the right hemithorax; damage at the level of the aorta causes left-sided effusions. 3

Diagnostic Criteria

When chylothorax is suspected, pleural fluid should be sent for measurement of triglyceride and cholesterol levels, with laboratory evaluation for cholesterol crystals and chylomicrons. 1

Objective diagnostic criteria include:

• Pleural fluid triglyceride level >110 mg/dL (>1.24 mmol/L) 2, 4
• Ratio of pleural fluid to serum triglyceride level >1.0 2, 4
• Presence of chylomicrons (confirmed by lipoprotein electrophoresis) 2, 5
• Triglyceride <50 mg/dL (<0.56 mmol/L) essentially excludes chylothorax 1

Etiologies

Traumatic Causes (54% of cases):

• Iatrogenic injury is most common, including esophageal resections, lung cancer resections, cardiovascular surgeries, and spinal surgeries. 4
• Accidental trauma to the thoracic duct. 3

Non-traumatic Causes (46% of cases):

• Malignancy accounts for approximately 50% of all chylothorax cases, with lymphoma being the most common (75% of malignant chylothoraces). 1, 4
• Other non-malignant causes include lymphangioleiomyomatosis, sarcoidosis, tuberculosis, amyloidosis, cirrhosis, heart failure, nephrotic syndrome, and venous thrombosis. 1, 4

Critical Distinction: Chylothorax vs. Pseudochylothorax

Chylothorax must be distinguished from pseudochylothorax ("cholesterol pleurisy"), which results from cholesterol crystal accumulation in long-standing pleural effusions with markedly thickened, fibrotic pleura. 1

Key differentiating features:

• Pseudochylothorax: cholesterol level >200 mg/dL (>5.18 mmol/L), no chylomicrons, cholesterol crystals present on microscopy. 1
• Chylothorax: high triglycerides, chylomicrons present, no cholesterol crystals. 1
• Chronic rheumatoid pleurisy is now the most common cause of pseudochylothorax (historically tuberculosis). 1

Common pitfall:

• Milky empyema can mimic chylothorax but can be distinguished by bench centrifugation, which leaves a clear supernatant in empyema as cell debris separates, while chylous effusion remains milky. 1

Clinical Significance

• The lymphocyte-rich composition contributes to risk of immunosuppression in chronic chyle leak. 2
• The high protein content explains the risk of malnutrition with ongoing losses, as repeated drainage causes loss of fat, proteins, and lymphocytes. 2, 3
• Chylothorax can lead to significant morbidity and mortality if not properly managed. 6