Lipid pleural effusions.

Traditionally, a lipid pleural effusion has been described as milky or turbid appearing. However, lipid effusions may have varied presentations making a diagnosis by appearance problematic. Distinguishing between a chylothorax and a cholesterol effusion, the 2 types of lipid effusions, is essential. A chylothorax develops after injury or obstruction of the thoracic duct, leading to a chyle leak into the pleural space that is characterized by an increased triglyceride concentration and the presence of chylomicrons. In contrast, a cholesterol effusion is a long-standing effusion associated with an elevated cholesterol concentration, usually greater than 250 mg/dL, a thick pleural rind, and represents a form of lung entrapment.