This follows the entrance of saprophytic organisms into lung tissue that has undergone degenerative changes. The primary necrosis may follow in the course of pneumonia, tuberculosis, embolism, and infarction. May also result from the aspiration of putrefactive material, as in gangrene of the larynx, foreign bodies in the bronchi; extension of disease of neighboring tissues, as in carcinoma of the esophagus with perforation.
A so-called idiopathic form occurs in alcoholics and in asthenic states. Is probably due to infection.
The involvement may be either diffuse or circumscribed. In the latter, there are usually numerous irregular areas of a dark brown, greenish, or black color. They are rather dry, and are surrounded by a zone of congestion and edema.
In the diffuse variety the condition is much more severe. It may follow the circumscribed form or occur primarily. The gangrene is of the moist variety, the affected area being soft, mushy, greenish in color, and having an extremely foul odor.
The broken-down tissue may be expectorated and leave a cavity through which blood-vessels and bronchi may pass. Generally the vessels are obliterated by means of an arteritis with thrombus formation. The artery may, however, be destroyed before such a protective measure has taken place and severe hemorrhage result.
General embolism with septicemia frequently occurs. If recovery follows the disappeared necrotic tissue is replaced by connective-tissue hyperplasia.
The sputum in gangrene of the lungs is extremely offensive and tends to separate into layers - an upper frothy one, a middle, yellowish and fluid, and a lower layer that is brownish and purulent. In the sediment are found particles of elastic tissue, lung tissue, triple phosphate crystals, margaric acid, pus cells, pigment, and fat drops. Numerous organisms of various kinds are also present.