Lung Abscess — Viva

Q1: Definition and diagnosis (2 min)

"A 55-year-old alcoholic has fever, foul-smelling sputum and this X-ray. What is it and why?"

• Lung abscess — a localised collection of pus in a cavitating area of lung parenchyma.[1]
• Classical features: thick-walled cavity with an air-fluid level, surrounding consolidation, dependent segment (posterior upper lobe / superior lower lobe in a recumbent patient)
• Foul-smelling (fetid) sputum = anaerobes — the highest-yield bedside clue
• The right lung is commoner because the right main bronchus is shorter, wider and more vertical

Q2: Aetiology and risk factors (2 min)

"List the causes of a lung abscess."

• Four mechanisms:
  • Aspiration (commonest) — alcohol, seizures, poor dentition, dysphagia, stroke, anaesthesia; mixed anaerobic flora
  • Necrotising pneumonia — Staph aureus (PVL/CA-MRSA), Klebsiella, Pseudomonas
  • Bacteraemic / septic-embolic — right-sided endocarditis in IVDU (Staph), Lemierre syndrome (Fusobacterium necrophorum)
  • Post-obstructive — distal to a tumour or foreign body
• Why is poor dentition a risk? It raises the bacterial load of the aspirate (not the volume) [1]

Q3: Management — the four pillars (3 min)

"How do you treat it?"

• 1. Antibiotics — clindamycin 600 mg IV TDS or amoxicillin-clavulanate 1.2 g IV TDS for 4 to 6 weeks; cover anaerobes and microaerophilic streptococci; IV-to-oral switch when afebrile and improving[1]
• 2. Drainage — for over 6 cm, refractory, imminent rupture, immunocompromised, or septic; method of choice is percutaneous CT-guided catheter drainage[2]
• 3. Treat the cause — dentition, swallow, alcohol, seizures, endocarditis, Lemierre
• 4. Exclude obstruction — bronchoscopy in any non-resolving abscess
• Metronidazole alone is inadequate (poor activity against microaerophilic streptococci and Actinomyces)

Q4: The non-resolving abscess (2 min)

"It's not resolving after 4 weeks. Now what?"

• Bronchoscopy to exclude an obstructing bronchogenic carcinoma or foreign body — the single most important step[1]
• A cavitating squamous-cell carcinoma mimics an abscess: thick, irregular, eccentric wall, an intracavitary mass, no surrounding consolidation, no response to antibiotics
• Also send sputum for AFB / GeneXpert to exclude tuberculosis; consider a fungal cavity in the immunocompromised
• A post-obstructive abscess cannot be cured by antibiotics until the obstruction is relieved

Q5: Complications (1 min)

"What can go wrong?"

• Rupture into the pleura → empyema with bronchopleural fistula (sudden copious foul sputum; place affected-side down to protect the contralateral lung; chest tube)
• Massive haemoptysis — affected-side down, protect the uninvolved lung, bronchial-artery embolisation, surgery
• Sepsis / septic shock, bacteraemia with metastatic infection (brain abscess, endocarditis), lung gangrene, ARDS
• In chronic cases, secondary amyloidosis and digital clubbing [1]