A localized cavity with pus, resulting from necrosis of lung tissue, with surrounding pneumonitis. Etiology and Pathology Lung abscesses are usually due to infected material from the upper airway aspirated when a patient is unconscious or obtunded from alcohol, other drugs, CNS disease, general anesthesia, coma, or excessive sedation. The causative organisms are usually anaerobes. Lung abscesses are often associated with periodontal disease, in which anaerobes are prevalent. Bacteria cultured from lung abscesses include common and nasopharyngeal flora, particularly anaerobes, and less often, aerobic bacteria or fungi.
Bronchogenic carcinoma is an occasional underlying cause in older smokers.
Cavitary TB is not considered a lung abscess but must be remembered in the differential diagnosis. Blastomycosis, histoplasmosis, and coccidioidomycosis may also cause acute or chronic lung abscesses and should be suspected in a person who has nonputrid abscesses and who lives in an endemic area. Less common causes of lung abscess include septic pulmonary emboli, secondary infection of pulmonary infarcts, and direct extension of amebic or bacterial abscesses from the liver through the diaphragm into the lower lobe of the lung. Single lung abscesses are most common. In abscesses due to aspiration, the superior segment of a lower lobe and the posterior segment of an upper lobe are affected most often.