A hemothorax is the accumulation of blood between the membranes lining the lungs (the pleura).
A hemothorax can occur due to trauma to the chest, or when blood vessels in the lungs break due to infections, emphysema, lung cancer, or lung surgery.
Symptoms may include shortness of breath, chest pain, and weakness. Treatment involves treating the cause of the bleeding and inserting a chest tube to drain the blood. In some cases surgery (a thoracotomy) is needed to control the bleeding.

