It is a localized area of necrosis of lung tissue with suppuration. It is of 2 types-
- Primary lung abscesses that develop in an otherwise normal lung, the commonest cause is the aspiration of infected materials.
- Secondary lung abscess that develops as a complication of some other disease of the lung.
-Common micro-organism introduced into the lungs are streptococci, staphylococci, and gram-negative organisms by following mechanisms
– Aspiration of infected foreign material.
– Preceding bacterial infection.
– Bronchial obstruction.
– Septic embolism.
It is more commonly occurs in the right lung due to the more vertical main bronchus and is frequently single. More commonly located in the lower part of the right upper lobe or apex of the right lower lobe.
It may be of variable size from few mm to large cavities, 5-6 cm in diameter and cavity contain exudate. An acute lung abscess is initially surrounded by acute pneumonia and poorly defined ragged wall, with long duration it becomes chronic and develops the fibrous wall.
The feature is the destruction of lung parenchyma with suppurative exudate in the lung cavity. Initially surrounded by acute inflammatory cells but later there is the replacement by chronic inflammatory cell-like lymphocytes, plasma cells and macrophages and in chronic cases, there is the formation of a collagenic wall.