Lung Abscess

Lung abscess is a localised area of lung parenchymal necrosis containing pus. It typically results from aspiration of oropharyngeal contents in a patient with impaired airway protective reflexes or periodontal disease.

It may occur as a complication of necrotising pneumonia, and is characterised by a polymicrobial anaerobic infection in the majority of primary cases.

Pathophysiology and aetiology

Aspiration of oropharyngeal secretions containing anaerobic organisms in a patient with reduced consciousness, alcohol intoxication, dysphagia, seizure disorder or poor dental hygiene leads to necrotising pneumonia in a dependent lung segment.

Classically this is the posterior segment of the right upper lobe or the apical segment of the right lower lobe, reflecting typical positioning during aspiration. It progresses over one to two weeks to cavitation and abscess formation.

Secondary lung abscess can also occur from haematogenous spread (septic emboli), bronchial obstruction (tumour, foreign body) or extension from a subphrenic or hepatic source.

Subacute onset over one to two weeks of fever, productive cough, weight loss and malaise characterises the typical presentation, with putrid, foul smelling sputum a highly characteristic and diagnostically useful feature reflecting the underlying anaerobic infection.

Risk factors including alcohol dependence, reduced consciousness, seizure disorder, dysphagia and poor dental hygiene should be actively sought in the history, and pleuritic chest pain occurs where there is associated pleural involvement.

Clubbing can develop with chronic, longstanding disease, and haemoptysis occurs in a proportion, reflecting the necrotising and cavitating nature of the process.

Chest radiography shows a cavitating lesion, typically with an air fluid level, in the characteristic dependent lung segments, with computed tomography providing greater anatomical detail, distinguishing a true parenchymal abscess from an empyema with a bronchopleural fistula, and helping exclude an underlying obstructing lesion.

Sputum culture, including anaerobic culture where feasible (though technically challenging given contamination by oral flora), and blood cultures support identification of the causative organism, though a specific microbiological diagnosis is not always achieved given the polymicrobial anaerobic nature of most primary aspiration associated abscesses.

Bronchoscopy is considered where an underlying obstructing lesion (tumour, foreign body) is suspected, particularly in an older patient, a smoker, or where the clinical picture is atypical for straightforward aspiration.

Prolonged antibiotic therapy is the mainstay of treatment.

• Clindamycin 600 mg intravenously three times daily, transitioning to oral clindamycin 300 to 450 mg four times daily once clinically improving. It is historically preferred given superior anaerobic coverage.
• Co amoxiclav 1.2 g intravenously three times daily transitioning to oral co amoxiclav 625 mg three times daily is now commonly used as an equally effective and better tolerated alternative, given lower rates of Clostridioides difficile associated diarrhoea compared with clindamycin.

Total antibiotic duration is typically prolonged, generally three to six weeks or longer, guided by clinical, radiographic and inflammatory marker response rather than a fixed short course, given the slow resolution characteristic of this condition, with radiographic resolution frequently lagging well behind clinical improvement.

Postural drainage and chest physiotherapy may support clearance of secretions, though evidence for specific benefit is limited and this is used adjunctively rather than as primary treatment.

Percutaneous or surgical drainage is reserved for large abscesses (typically greater than 6 cm), those not responding to antibiotic therapy alone after an adequate trial, or where there is diagnostic uncertainty requiring tissue or fluid sampling.

Surgical resection is reserved for the minority of cases failing both antibiotic therapy and less invasive drainage approaches.

Dental assessment and treatment of periodontal disease, and addressing any underlying predisposing factor (alcohol dependence, seizure control, swallowing assessment for dysphagia), form an important component of comprehensive management and prevention of recurrence.