Lung abcess

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Lung abcess is the culmination of a severe acute bacterial infection of the lung with tissue destruction, necrosis. Other processes can be involved. There is often a combination of an anatomical abnormality like Bronchiectasis or a physiological insult like Aspiration with one or a mixture of pathogenic organisms. The site for a lung abcess often depends on the most dependant part. The apical segment of the lower lobe is often involved with unconscious patients, who may lie supine with the apical lower bronchus pointing straight back.

The antibiotic era has rendered septic embolus from existing extrapulmonary focus a rarer cause of lung abcess. The converse is more common. Never neglect the chest X-ray in brain abcess or septic embolisation.

The organisms or mixture of organisms are important in the aetiology, depending on the different toxins and enzymes that are produced. The fluid accumulation, tissue liquifaction and local vasculitis can compromise local circulation and add infarction to the destructive processes. Staphylococcus aureus infection frequently cavitates, giving pneumatocoeles. Klebsiella, Pseudomonas and Proteus all may produce a cavitating pneumonia. Since anaerobic infection in an organ dedicated to air exchange is unlikely, unless in a mixed infection from aspiration of infected material, the presence of gas in an area of necrotic consolidation requires a communication with a bronchus.

Sub-normal cell mediated immunity may increase the probability of abcess and pneumatocoele, as in HIV, leukaemias and inherited white cell defects.

Various anatomic expressions of pathology.

	involving Right lower lobe
	involving left lower lobe
	cavitating pneumonia involving right upper lobe
	cavitating pneumonia involving Left lower lobe
	involving Pneumatocoele

Ian Maddison 1998