39. Lung abscess, lung gangrene and bronchiectasis

1. Definition

• Lung abscess → circumscribed cavity of pus or necrosis in the lung parenchyma caused by infection, > 2 cm, often with an air-fluid level
• Lung gangrene → diffuse putrid necrosis of lung tissue with no clear demarcation from living lung; extreme form of necrotising pneumonia
• Bronchiectasis → chronic disease with permanent, abnormal dilatation of the bronchi, chronic cough, sputum and infection

2. Epidemiology

• Lung abscess → men, age 40–60 years, alcohol misuse, poor dental hygiene
• Lung gangrene → rare; debilitated or immunocompromised patients; high mortality
• Bronchiectasis → more common in women and older adults; cystic fibrosis in the young

3. Aetiology and risk factors

Lung abscess

• Aspiration → most common cause:
  • Reduced consciousness → alcohol, drugs, seizures, anaesthesia, stroke
  • Dysphagia, oesophageal disease
  • Poor dental hygiene, gingivitis
• Organisms → anaerobes from the mouth (Peptostreptococcus, Prevotella, Bacteroides, Fusobacterium), often polymicrobial
• Others → Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus anginosus (milleri), Pseudomonas, Nocardia, fungi in the immunocompromised
• Bronchial obstruction → tumour, foreign body
• Septic emboli → right-sided endocarditis, intravenous drug use
• Infected cyst, bulla or infarct

Lung gangrene

• Severe pneumonia with Klebsiella, S. aureus, anaerobes, Pseudomonas
• Diabetes, alcohol misuse, immunosuppression
• Thrombosis of pulmonary vessels in the infected area

Bronchiectasis

• Two factors → infection + impaired drainage, obstruction or poor host defence
• Post-infective → childhood pneumonia, measles, whooping cough, tuberculosis
• Cystic fibrosis
• Primary ciliary dyskinesia → Kartagener's syndrome (situs inversus, sinusitis, bronchiectasis)
• Immunodeficiency → hypogammaglobulinaemia
• Allergic bronchopulmonary aspergillosis (ABPA)
• Obstruction → foreign body, tumour, nodes (middle lobe syndrome)
• α1-antitrypsin deficiency, rheumatoid arthritis, inflammatory bowel disease
• Organisms → Haemophilus influenzae, Pseudomonas aeruginosa, Moraxella, S. aureus

4. Pathogenesis

Lung abscess

1. Aspiration of infected oropharyngeal material
2. Pneumonitis in a dependent segment
3. Necrosis and liquefaction over 1–2 weeks
4. Drainage into a bronchus → cavity with air-fluid level
5. Fibrous wall forms → chronic abscess after 6 weeks
6. Supine → posterior segment of the upper lobe, apical (superior) segment of the lower lobe; right more often (straighter right main bronchus)
7. Upright → basal segments of the lower lobes

Lung gangrene

1. Severe necrotising pneumonia
2. Vascular thrombosis
3. Spreading putrid necrosis with no capsule
4. Sloughs of dead lung in the cavity; sepsis

Bronchiectasis

1. Infection and poor clearance
2. Neutrophilic inflammation → elastase destroys the bronchial wall
3. Bronchial dilatation, mucus plugging
4. More infection → "vicious cycle"
5. Hypertrophied bronchial arteries → haemoptysis

5. Classification

Lung abscess

• By duration → acute (< 6 weeks), chronic (> 6 weeks)
• By cause → primary (aspiration, pneumonia in a healthy host) or secondary (obstruction, immunosuppression, emboli)
• By number → single or multiple

Bronchiectasis

• By shape:
  1. Cylindrical (tubular) → mildest
  2. Varicose → beaded
  3. Cystic (saccular) → most severe
• By extent → localised (one lobe) or diffuse (bilateral)

6. Clinical picture

Symptoms

• Lung abscess:
  • Fever, rigors, night sweats, weight loss over weeks
  • Cough with large volumes of foul-smelling (putrid) sputum after drainage into a bronchus
  • Pleuritic chest pain, haemoptysis
• Lung gangrene:
  • Severe sepsis, septic shock
  • Very foul, dark, copious sputum with pieces of lung tissue
• Bronchiectasis:
  • Chronic productive cough, daily purulent sputum, worse in the morning and on lying down
  • Recurrent chest infections
  • Haemoptysis → mild to massive
  • Dyspnoea, fatigue, sinusitis

Signs

• Poor dentition, foul breath
• Dullness, bronchial breathing over consolidation
• Amphoric breath sounds over a large cavity
• Bronchiectasis → coarse crackles over the affected area, finger clubbing, wheeze

7. Diagnosis

Laboratory

• Full blood count → leucocytosis; C-reactive protein
• Sputum Gram stain, culture, acid-fast bacilli (tuberculosis)
• Blood cultures
• Bronchiectasis work-up → sweat test (cystic fibrosis), immunoglobulins, Aspergillus serology, α1-antitrypsin

Imaging

• Chest X-ray → thick-walled cavity with air-fluid level (abscess); "tram lines" and ring shadows (bronchiectasis)
• CT chest → separates abscess from empyema, shows cavitating cancer
• Abscess on CT → round, thick wall, acute angle with the chest wall; empyema → lenticular, obtuse angle, "split pleura" sign
• Gangrene → spreading consolidation with multiple small cavities and sloughs
• High-resolution CT (HRCT) → gold standard for bronchiectasis:
  • Signet ring sign → bronchus wider than the adjacent artery
  • Bronchi seen within 1 cm of the pleura
  • No tapering of bronchi

Bronchoscopy

• Exclude obstructing tumour or foreign body, especially over 50 years or in smokers
• Bronchoalveolar lavage for culture
• Locate the bleeding source in haemoptysis

8. Differential diagnosis

• Cavitating lung cancer (squamous cell)
• Tuberculosis
• Empyema with bronchopleural fistula
• Infected hydatid cyst or bulla
• Granulomatosis with polyangiitis (Wegener's)
• Pulmonary infarction
• Aspergilloma
• Bronchiectasis versus COPD, chronic bronchitis

9. Treatment

Conservative

• Lung abscess:
  • Prolonged antibiotics → covering anaerobes: β-lactam with β-lactamase inhibitor (co-amoxiclav, ampicillin-sulbactam), or carbapenem, or clindamycin; IV then oral
  • Duration → 3–6 weeks or until the cavity resolves
  • Postural drainage, physiotherapy
  • Treat the cause → dental care, swallowing assessment
  • 85–95% respond to medical treatment; complete healing in 3–4 months
  • Poor response if → symptoms > 3 months, cavity > 4–6 cm, obstructed bronchus
  • Not responding → CT-guided percutaneous drainage or bronchoscopic drainage
• Lung gangrene → resuscitation, broad-spectrum IV antibiotics, organ support; early surgery if sepsis is not controlled
• Bronchiectasis:
  • Airway clearance → physiotherapy, active cycle of breathing, postural drainage
  • Antibiotics for exacerbations → 14 days, guided by sputum culture
  • Frequent exacerbations (≥ 3 a year) → long-term macrolide (azithromycin), inhaled antibiotics for Pseudomonas
  • Bronchodilators, vaccination, treat cause (immunoglobulin, ABPA)
  • Massive haemoptysis → bronchial artery embolisation first

Surgical

• Lung abscess → resection (usually lobectomy):
  • Persistent thick-walled cavity ≥ 2 cm after treatment
  • Sepsis not cleared after 8 weeks of medical treatment
  • Massive haemoptysis
  • Suspected carcinoma
  • Complications → rupture into pleura (empyema), bronchopleural fistula
• Lung gangrene → anatomical resection (lobectomy or pneumonectomy) of dead lung once stabilised
• Bronchiectasis:
  • Localised disease with frequent exacerbations despite best medical treatment
  • Massive haemoptysis not controlled by embolisation
  • Destroyed lobe
  • Usually segmentectomy or lobectomy, VATS preferred
  • Bilateral, diffuse disease → relative contraindication; lung transplant in end-stage disease (cystic fibrosis)
• Massive haemoptysis (> 150 mL in 24 h or > 100 mL/h):
  1. Protect the airway, oxygen
  2. Lie the patient bleeding side down
  3. Large-bore endotracheal tube or single-lung intubation
  4. Bronchoscopy to locate and control (cold saline, adrenaline, balloon)
  5. Bronchial artery embolisation
  6. Resection if bleeding continues
• Lung resection for sepsis → double-lumen tube to protect the healthy lung from spillage

10. Complications

• Empyema, pyopneumothorax
• Bronchopleural fistula
• Massive haemoptysis → death from asphyxia, not blood loss (mortality 7–30%)
• Spread to the other lung
• Brain abscess
• Septic shock, multiorgan failure
• Secondary amyloidosis (chronic suppuration)
• Respiratory failure, cor pulmonale (bronchiectasis)