Minor degrees of subcutaneous emphysema and pneumothorax associated with fractured ribs or penetrating chest wounds are not uncommon. Usually this tissue air is spontaneously absorbed with little or no difficulty to the patient, and the physician is likely not to give it a second thought. Occasionally however, subcutaneous emphysema will become very widespread and create an alarming picture. In most such instances there is also a mediastinal emphysema which can produce enough tension within the mediastinum to threaten the patient's life. Since the mediastinal emphysema is a dangerous condition, this problem will be emphasized in the present discussion. Just how does air become trapped within the mediastinum?
PATHOGENESIS OF MEDIASTINAL EMPHYSEMA
In 1945, Hamman1 gave an excellent review of this entire subject, especially from an internist's viewpoint. He pointed out various pathways followed by air in reaching or leaving the mediastinum and described the clinical manifestations and diagnosis. Loud