Characteristics

• Cavitating infective consolidation.

• Single or multiple lesions.

• Bacterial (Staphylococcus aureus, Klebsiella, Proteus, Pseudomonas, TB and anaerobes) or fungal pathogens are the most common causative organisms.

• ‘Primary’ lung abscess – large solitary abscess without underlying lung disease is usually due to anaerobic bacteria.

• Associated with aspiration and/or impaired local or systemic immune response (elderly, epileptics, diabetics, alcoholics and the immunosuppressed).

Clinical features

• There is often a predisposing risk factor, e.g. antecedent history of aspiration or symptoms developing in an immunocompromised patient.

• Cough with purulent sputum.

• Swinging pyrexia.

• Consider in chest infections that fail to respond to antibiotics.

• It can run an indolent course with persistent and sometimes mild symptoms. These are associated with weight loss and anorexia mimicking pulmonary neoplastic disease or TB infection.

Radiological features

• Most commonly occur in the apicoposterior aspect of the upper lobes or the apical segment of the lower lobe.

• CXR may be normal in the first 72 h.

• CXR – a cavitating essentially spherical area of consolidation usually > 2 cm in diameter, but can measure up to 12 cm. There is usually an air-fluid level present.

• Characteristically the dimensions of the abscess are approximately equal when measured in the frontal and lateral projections.

• CT is important in characterising the lesion and discriminating from other differential lesions. The abscess wall is thick and irregular and may contain locules of free gas. Abscesses abutting the pleura form acute angles. There is no compression of the surrounding lung. The abscess does not cross fissures. It is important to make sure no direct communication with the bronchial tree is present (bronchopleural fistula).