Lung abscess

Lung abscess is necrosis of the pulmonary tissue and formation of cavities (more than 2 cm)^[1] containing necrotic debris or fluid caused by microbial infection.

This pus-filled cavity is often caused by aspiration, which may occur during altered consciousness. Alcoholism is the most common condition predisposing to lung abscesses.

Lung Abscess is considered primary(60%^[2]) when it results from existing lung parenchymal process and is termed secondary when it complicates another process e.g. vascular emboli or follows rupture of extrapulmonary abscess into lung.

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Causes

Conditions contributing to lung abscess

• Aspiration of oropharyngeal or gastric secretion
• Septic emboli
• Necrotizing pneumonia
• Vasculitis: Wegener's granulomatosis
• Necrotizing tumors: 8% to 18% are due to neoplasms across all age groups, higher in older people; primary squamous carcinoma of the lung is the commonest.

Organisms

In the post-antibiotic era pattern of frequency is changing. In older studies anaerobes were found in up to 90% cases but they are much less frequent now^[3].

• Anaerobic bacteria: Peptostreptococcus, Bacteroides, Fusobacterium species,
• Microaerophilic streptococcus : Streptococcus milleri
• Aerobic bacteria: Staphylococcus, Klebsiella, Haemophilus, Pseudomonas,Nocardia, Escheria coli, Streptococcus, Mycobacteria^[4]
• Fungi: Candida, Aspergillus
• Parasites: Entamoeba histolytica,

Symptom and sign

Onset of symptoms is often gradual, but in necrotizing staphylococcal or gram-negative bacillary pneumonias patients can be acutely ill. Cough, fever with shivering and night sweats are often present. Cough can be productive with foul smelling purulent sputum (≈70%) or less frequently with blood (i.e. hemoptysis in one third cases) ^[5]. Affected individuals may also complaint chest pain, shortness of breath, lethargy and other features of chronic illness.

Patients are generally cachectic at presentation. Finger clubbing is present in one third of patients^[5]. Dental decay is common especially in alcoholics and children. On examination of chest there will be features of consolidation such as localised dullness on percussion, bronchial breath sound etc.

Diagnosis

Chest Xray and other imaging studies

Abscess is often unilateral and single involving posterior segments of the upper lobes and the apical segments of the lower lobes as these areas are gravity dependent when lying down. Presence of air-fluid levels implies rupture into the bronchial tree or rarely growth of gas forming organism.

Laboratory studies

Raised inflammatory markers ( high ESR, CRP) are usual but not specific. Examination of sputum is important in any pulmonary infections and here often reveals mixed flora. Transtracheal of Transbronchial (via bronchoscopy) aspirates can also be cultured. Fibre optic bronchoscopy is often performed to exclude obstructive lesion; it also helps in bronchial drainage of pus.

Management

Broadspectrum antibiotic to cover mixed flora is the mainstay of treatment. Pulmonary physiotherapy and postural drainage are also important. Surgical procedures are required in selective patients for drainage or pulmonary resection.

Complications

Rare now a days but include spread of infection to other lung segments, bronchiectasis, empyema, and bacteraemia with metastatic infection such as brain abscess^[2].

Prognosis

Most cases respond to antibiotic and prognosis is usually excellent unless there is a debilitating underlying condition. Mortality from lung abscess alone is around 5% and is improving.

See also

• Other chronic lung infections
  • Empyema
  • Bronchiectasis
• Abscess
• Pleural effusion

References