Lung Abscess

⚠️ Poor Prognosis: Advanced age, aspiration risk, immunosuppression, bronchial obstruction, and underlying malignancy are markers of poor outcome.

📖 About

• Lung abscess = localised collection of pus within the pulmonary parenchyma resulting from suppurative necrosis of lung tissue and cavity formation with an air–fluid level.
• Classically follows aspiration pneumonia in patients with altered consciousness (e.g., alcohol intoxication, seizures, stroke, anaesthesia).
• Represents the “end‑point” of severe infection: tissue necrosis → liquefaction → bronchial communication → cavity drainage.
• Commonly affects the posterior segments of upper lobes and superior segments of lower lobes due to gravity during aspiration.

🧬 Pathophysiology

• Aspiration of anaerobic bacteria → local infection and microvascular thrombosis → tissue necrosis.
• Liquefactive necrosis leads to formation of a cavity containing pus, bacteria, and necrotic debris.
• Drainage into a bronchus → expectoration of purulent, foul‑smelling sputum (“fetid abscess”).
• Progression may form a bronchopleural fistula or rupture into the pleural space → secondary empyema.

📂 Classification

• Primary lung abscess: Occurs in previously healthy lungs, usually after aspiration of oropharyngeal contents.
• Secondary lung abscess: Occurs due to pre‑existing lung or systemic disease (e.g., obstructing carcinoma, bronchiectasis, HIV, diabetes, immunosuppression).
• Acute: < 6 weeks; Chronic:  > 6 weeks or persistent cavity.

🦠 Microbiology / Causes

• Aspiration (anaerobes ≈ 80 %): Prevotella, Bacteroides, Fusobacterium, Peptostreptococcus.
• Facultative bacteria: Staphylococcus aureus, Streptococcus pyogenes, Klebsiella, Pseudomonas.
• Immunocompromised hosts: Nocardia, Aspergillus, Candida, Mycobacterium tuberculosis.
• Post‑obstructive: Bronchial carcinoma, foreign body, mediastinal mass.
• Haematogenous (septic emboli): Right‑sided endocarditis, infected jugular thrombophlebitis, I.V. drug use (often Staph. aureus).

🩺 Clinical Features

• Fever, chills, weight loss, malaise.
• Persistent productive cough with foul‑smelling purulent sputum or “sputum flooding” when cavity drains.
• Haemoptysis common due to erosion of bronchial arteries.
• Pleuritic chest pain if peripheral lesion abuts pleura.
• Halitosis and metallic taste from anaerobic flora.
• Clubbing and cachexia in chronic infection.

🧾 Differential Diagnosis

• Cavitating squamous carcinoma (thick irregular wall, spiculated margins).
• Tuberculosis with apical cavities; often thinner walls, satellites.
• Wegener’s granulomatosis / vasculitis.
• Pulmonary infarction secondary to embolism with sterile cavitation.
• Cavitating pneumonia (Staph aureus, Klebsiella) vs true abscess = liquefied, thick‑walled cavity + air–fluid level.

🔎 Investigations

• Blood tests: Leukocytosis, ↑ ESR/CRP, ± anaemia of chronic disease.
• Chest X‑ray: Cavity with air–fluid level within consolidation, usually posterior segments of upper / superior of lower lobes.
• CT Thorax (contrast HRCT): Defines extent, number of lesions, wall thickness (typically > 2 mm), detects neoplasm or empyema.
• Bronchoscopy: Rule out endobronchial obstruction or neoplasm; may permit lavage or drainage.
• Microbiology:
  • Sputum / BAL / aspirate cultures for aerobes and anaerobes.
  • Blood cultures before antibiotics.
  • Aspiration for Gram stain or AFB if TB suspected.

💊 Management - Multidisciplinary Approach

• General / Supportive:
  • Postural drainage - dependent segment uppermost to facilitate drainage gravity‑wise (3–5× daily).
  • Physiotherapy and chest percussion to mobilise secretions.
  • Hydration and nutritional support to counter catabolic state.
  • Meticulous oral care to reduce anaerobic floral load.
• Antibiotic Therapy: (IV → PO 6–8 weeks till radiologic resolution)
  • First‑line: Co‑amoxiclav 1.2 g IV TDS or amoxicillin‑clavulanate PO 625 mg TDS if mild.
  • Penicillin‑allergic: Clindamycin 600 mg IV/PO QDS.
  • Aerobic Gram‑negatives suspected: Add ciprofloxacin 750 mg BD or levofloxacin 500 mg BD.
  • MRSA risk / post‑influenza: Add vancomycin or linezolid pending sensitivities.
  • Fungal / Nocardia: Voriconazole / TMP‑SMX based on culture.
• Re‑evaluation: Persistent fever > 10–14 days → repeat CT for non‑draining cavity or secondary malignancy.
• Surgical / Interventional Indications:
  • Abscess > 6 cm or > 6 weeks non‑responsive to therapy.
  • Massive haemoptysis.
  • Suspected bronchial obstruction or neoplasm after bronchoscopy.
  • Developing empyema / bronchopleural fistula → thoracostomy or lobectomy.

⚠️ Complications

• Empyema (thoracic infection extends to pleural space).
• Bronchopleural fistula → persistent air leak and pneumothorax.
• Massive haemoptysis from erosion of bronchial arteries.
• Sepsis  /  septic embolisation to brain or other organs.
• Chronic fibrocystic changes or mycetoma formation in residual cavity.

📋 Table – Diagnostic and Therapeutic Pearls

📚 References

• Leeds Teaching Hospital – Lung Abscess Guide
• StatPearls – Lung Abscess
• BMJ Thorax – Anaerobic Infections of the Lung