Orientation notes for study. Check local guidelines before prescribing.
Definition
A lung abscess is a localised area of necrosis of lung parenchyma with a cavity (usually 2 cm or more) containing pus or necrotic debris, caused by infection. Several small cavities (below 2 cm) in a pneumonic area are necrotising pneumonia.
Classification
- Primary lung abscess: arises in previously normal lung, usually after aspiration.
- Secondary lung abscess: arises on underlying disease: bronchial obstruction (tumour, foreign body), bronchiectasis, septic emboli, TB cavity, pulmonary infarction, immunosuppression.
- Acute (below 6 weeks) or chronic (over 6 weeks).
Causes and risk factors
- Aspiration (the commonest route): alcohol excess, seizures, stroke, reduced consciousness, dysphagia, anaesthesia, poor dental hygiene and gingivitis, GORD.
- Organisms: mostly anaerobes (Peptostreptococcus, Fusobacterium, Prevotella, Bacteroides), mixed with streptococci; Staphylococcus aureus (post-influenza, IV drug use, septic emboli, right-sided endocarditis); Klebsiella pneumoniae (alcoholics, diabetics); Pseudomonas and gram-negatives (hospital); TB; fungi (Aspergillus, Cryptococcus) and PCP/Nocardia in HIV; amoebic abscess by rupture of a liver abscess through the diaphragm.
- Obstruction by bronchial carcinoma (always exclude in older smokers).
- Immunosuppression: HIV, diabetes, chemotherapy, steroids, malnutrition.
Clinical features
- Insidious or subacute: fever, night sweats, cough with large volumes of purulent and often foul-smelling sputum (suggests anaerobes), weight loss, malaise, pleuritic pain, haemoptysis.
- Signs: finger clubbing (develops within weeks), poor dental hygiene, bronchial breathing, amphoric sound, crackles and pleural rub over the lesion; sometimes a pleural effusion.
Investigations
- Chest X-ray: a thick-walled cavity with an air-fluid level, typically in the posterior segment of the right upper lobe or apical segment of the lower lobe (dependent segments, aspiration).
- CT chest with contrast: location, size, wall thickness, underlying tumour or obstruction, empyema versus abscess.
- Blood: FBC (leucocytosis), CRP, ESR, cultures.
- Sputum: Gram stain, culture, AFB and GeneXpert for TB, fungal culture; bronchoscopy with lavage if no response or obstruction is suspected; CT-guided aspiration selectively.
- Exclude TB and cancer (cavitating squamous carcinoma), fungal disease and other cavities (granulomatosis with polyangiitis, infarct, hydatid cyst).
- HIV test and diabetes screening.
Management
- Prolonged antibiotics (usually 4–6 weeks, or until the cavity has resolved or become small and stable on X-ray). Start IV, then step down to oral:
- Amoxicillin-clavulanate (or ampicillin-sulbactam), or clindamycin; benzylpenicillin plus metronidazole is a traditional alternative.
- Add cover for Staph aureus (flucloxacillin, or vancomycin if MRSA) or gram-negatives according to the clinical setting and culture.
- Postural drainage and chest physiotherapy.
- Nutrition, treat alcohol use, dental care, treat diabetes.
- Drainage: percutaneous catheter drainage (CT or ultrasound guided) if large, failing to respond at 7–14 days, or if empyema coexists; bronchoscopic drainage is sometimes used.
- Surgery (lobectomy) for massive haemoptysis, failure of medical and drainage treatment, suspected cancer, or a large chronic abscess.
- Treat the underlying cause (tumour, obstruction, endocarditis, TB).
Complications
- Empyema and bronchopleural fistula, massive haemoptysis, spread (brain abscess, meningitis), sepsis, amyloidosis (chronic), chronic cavity that becomes colonised by Aspergillus (aspergilloma), recurrent infection.
Differential diagnosis
- TB cavity, cavitating carcinoma, empyema, fungal infection, hydatid cyst, granulomatosis with polyangiitis, pulmonary infarct, bronchiectasis, loculated pneumothorax.
Exam points
- Aspiration, anaerobes, foul sputum, air-fluid level = lung abscess.
- Right upper lobe posterior segment and lower lobe apical segment (dependent when lying down).
- Always exclude TB and carcinoma in Kenya.
- Antibiotics for weeks, not days.
- Drain if it fails medical treatment.
Pharmacology at a glance
Tap a drug name for its full card (how it works, adverse effects, cautions, dose), then use Back to this note to return to this spot. Condition guide: lung abscess drugs.
| Drug | Class | Role here | Watch for |
|---|---|---|---|
| Co-amoxiclav | Penicillin plus β-lactamase inhibitor | First-line for 4–6 weeks (anaerobes and mixed flora) | Diarrhoea, liver injury |
| Clindamycin | Lincosamide | Alternative first-line, good abscess penetration | C. difficile colitis |
| Benzylpenicillin | Penicillin | IV with metronidazole in the traditional regimen | Allergy |
| Metronidazole | Nitroimidazole | Anaerobic cover | Metallic taste, neuropathy with long courses; no alcohol |
| Flucloxacillin | Anti-staphylococcal penicillin | Staphylococcus aureus (septic emboli, post-influenza) | Cholestatic jaundice |
| Vancomycin | Glycopeptide | MRSA | Kidney injury, infusion reaction; level monitoring |
| Ceftriaxone | Third-generation cephalosporin | Gram-negative cover in hospital | Biliary sludge, allergy |
Weeks, not days: treat until the cavity has resolved or is small and stable, and always exclude TB and cancer.
Practice questions
1. A 52-year-old alcoholic man has 3 weeks of fever, weight loss and large amounts of foul-smelling sputum. Chest X-ray: a cavity with an air-fluid level in the right upper lobe. The most likely organisms are: A. Mycoplasma · B. Anaerobes (mixed oral flora) · C. Respiratory syncytial virus · D. Haemophilus alone · E. Legionella Answer: B.
2. A man with a lung abscess has no improvement after 2 weeks of antibiotics and the cavity has enlarged. The next step is: A. Stop antibiotics · B. CT-guided drainage and bronchoscopy to exclude obstruction or cancer · C. Steroids · D. Reassurance · E. Increase oxygen Answer: B.
3. The usual duration of antibiotic treatment for lung abscess is: A. 3 days · B. 7 days · C. 10 days · D. 4–6 weeks (until radiological resolution) · E. 6 months Answer: D.