Hemothorax is a collection of blood in the space between the chest wall and the lung (the pleural cavity).
The most common cause of hemothorax is chest trauma. It can also occur in patients who have:
Eckstein M, Henderson S. Thoracic trauma. In: Marx J, ed. Rosen's Emergency Medicine: Concepts and Clinical Practice. 6th ed. Philadelphia, Pa: Mosby Elsevier; 2006: chap 42.