Gross & microscopic appearance	Pathologic basis of disease	Clinical correlation	
Gross:
•	Patchy distribution.
•	Pale tan regions of parenchyma are normal.
•	Reddish brown regions of parenchyma are consolidated & contain hemorrhage & neutrophils.
•	Nodular, elevated, firm, airless regions with focal areas of palpable consolidation & suppuration.
•	Lesions are usually in the lower lobes.
•	At the lung base the changes are more advanced, coalesce & become confluent.

Microscopic:
•	Bronchiole becomes inflamed.
•	Ciliated epithelium is destroyed.
•	Suppurative exudate filling airways & airspaces.
•	Congestion of vessels & emigration of neutrophils
•	Organization may occur & result in fibrous scarring.	Etiology:
•	Variety of aspirated organisms.
•	Healthy individuals: streptococci, pneumococci
•	Following viral (e.g. influenza, measles) infection: staphylococci.
•	Children with viral infection: Haemophilus influenzae.
•	Community acquired in patients with depressed pulmonary defenses, e.g. chronic bronchitis: Klebsiella or Pseudomonas spp.
•	Hospital acquired: Pseudomonas spp.
•	Chronic alcoholics, diabetics: Klebsiella, coliforms

Frequently in:
•	Terminal event in a chronic debilitating disease
•	Infancy
•	Old age
•	Manifestation of secondary infection in viral conditions, e.g. influenzae, measles.

Pathogenesis:
•	Aspiration of organisms results in inflammation & necrosis of underlying parenchyma.
•	Spreading inflammation of terminal bronchioles and alveoli.
•	Lesions are initially focal, involving one or more lobules: first red, the grey, they show a central bronchiole containing pus.	Symptoms:
•	Fever
•	Cough
•	Purulent sputum

Complications:
•	Death: complicating of debilitating disease.
•	Resolution: often incomplete; it resulting fibrosis is gross, the lung structure may be distorted & changes in the larger bronchi cause bronchiectasis.
•	Suppurative changes: lung abscesses & empyema in debilitated patients.