Chylous effusion

**Definition:** A chylous effusion (chylothorax) is defined by the presence of chyle in the pleural space resulting from obstruction or disruption of the thoracic duct or one of its major tributaries. A triglyceride concentration > 110 mg/dL is virtually diagnostic, but the presence of chylomicrons confirms the diagnosis. However, a chylothorax defined by these criteria represents a heterogeneous group of clinical entities. The presence of chylomicrons or triglyceride levels > 110 mg/dL in a pleural effusion should be considered evidence of chyle leakage of indeterminate clinical significance. Many cases of a chylous effusion may be associated with other causes of pleural fluid formation.