This section is from the book "A Manual Of Pathology", by Guthrie McConnell. Also available from Amazon: A Manual Of Pathology.
Purulent Pneumonia is one caused by pyogenic organisms. In it there is found a purulent and hemorrhagic exudation, both in the alveoli and fibrous septa. The infection may take place through the bronchi, bronchogenic; the blood, hematogenic; or through the lymphatics of the pleura, pleurogenic.
The bronchogenic variety is most marked in the aspiration pneumonias that follow suppurative lesions of the upper air-passages. Large and small purulent collections are found, both in the alveolar walls and within the alveoli as well.
The hematogenic form is secondary to purulent areas in other parts of the body. The infectious agents gain entrance into the circulation, and as emboli are carried to the capillaries of the lung. Becoming lodged they set up secondary suppurative changes. Hemorrhagic infarctions are frequently found. The central part is necrotic, while around it is found a zone of severe infiltration. The entire area may soften, break down and form cavities. The abscesses quite frequently evacuate into a bronchus or sometimes into the pleural cavity, giving rise to empyema, a purulent pleurisy. Gangrene of the lung may occur.