Localised infection and destruction of lung tissue leading to a collection of pus within the lung.
Tuberculosis is the most common cause of lung abscesses but is considered separately. Organisms which cause cavitation and hence lung abscess include Staphylococcus and Klebsiella. It is more common in aspiration pneumonia or bronchial obstruction (by bronchial carcinoma or a foreign body).
The abscess may form during the course of an acute pneumonia, or chronically in partially treated pneumonia. Multiple lung abscesses may form from septic emboli, e.g. from right-sided infective endocarditis or an infected central line. Infarcted lung may cavitate, and rarely it becomes secondarily infected.
Patients present with worsening features of pneumonia, usually with a swinging pyrexia, and can be severely ill. If there is communication between the abscess and the airways the patient coughs up large amounts of foul sputum. Clubbing may develop.
Anaemia, a high neutrophil count and raised inflammatory markers (ESR, CRP) are common. X-ray demonstrates one or more round opacities often with a fluid level. Sputum and blood cultures may be positive, but bronchoscopy may be necessary to exclude obstruction, to look for underlying carcinoma, and to obtain biopsies and broncho-alveolar lavage for microbiology. Some-times CT or ultrasound guided aspiration is needed and can also be therapeutic with insertion of a drain. Echocardiogram should be considered to look for infective endocarditis.
Breach of the pleura results in an empyema.
Postural drainage, physiotherapy and a prolonged course of appropriate antibiotics to cover both aerobic and anaerobic organisms will resolve most smaller abscesses. Larger abscesses may require repeated aspiration, drainage and even surgical excision.