Chylothorax occurs when chyle from the thoracic duct empties into the pleural space. Chyle is a milky white fluid with a high concentration of triglycerides, chylomicrons, and white blood cells. Pseudochylothorax is pleural fluid that mimics true chylous pleural effusion in appearance but lacks the biochemical criteria for chylothorax; usually due to a longstanding pleural effusion