Lung Abscess

Classification

Etiology & Predisposing Factors

• Altered consciousness (alcoholism, drug overdose, seizures, anesthesia)
• Bulbar dysfunction, prior stroke, neuromuscular disease
• Esophageal dysmotility, GERD, gastric distension
• Poor dentition / periodontal disease (anaerobic colonization of gingival crevices)

• Necrotizing pneumonia - from S. aureus, Streptococcus pyogenes, Klebsiella pneumoniae, Pseudomonas spp.
• Bronchial obstruction - especially lung carcinoma (impaired drainage + atelectasis)
• Septic emboli - right-sided infective endocarditis (typically S. aureus), Lemierre's syndrome (Fusobacterium necrophorum)
• Hematogenous spread - staphylococcal bacteremia → multiple abscesses
• Fungi/mycobacteria - Aspergillus, Cryptococcus, Histoplasma, M. tuberculosis can mimic or cause cavitary disease

Microbiology

• Anaerobes are present in up to 93% of cases and are the sole isolates in 1/3 to 2/3 of primary abscesses - Fishman's Pulmonary Diseases
• Most common anaerobes: Prevotella, Fusobacterium, Bacteroides, Peptostreptococcus, and microaerophilic streptococci (oral commensals)
• In immunocompromised hosts: Pseudomonas aeruginosa, gram-negative rods, Nocardia, Aspergillus, Cryptococcus
• Metronidazole alone is NOT effective as single-agent therapy - it misses microaerophilic streptococci - Harrison's, p. 1079

Location (Morphology)

• Right side > Left side (more vertical right mainstem bronchus)
• Posterior segment of right upper lobe and apical segments of lower lobes - dependent segments in a recumbent person
• Aspiration-related: usually single
• Pneumonia/bronchiectasis-related: often multiple, basal, bilateral
• Hematogenous: multiple, scattered
• Abscess size ranges from a few mm to 5-6 cm in diameter

CT Scan Example

Clinical Features

• Indolent onset over weeks to months (especially anaerobic)
• Fever, cough, purulent or foul-smelling sputum (putrid = anaerobic)
• Night sweats, weight loss, anemia (chronic systemic features)
• Hemoptysis (variable)
• On CXR: cavity with air-fluid level after drainage into an airway

Diagnosis

• Chest X-ray: Infiltrate with cavity, often with air-fluid level
• CT chest (preferred): Better delineates cavitation, distinguishes parenchymal abscess from pleural collection (empyema), detects associated mass lesions
• Sputum culture, blood cultures
• Bronchoscopy: to obtain cultures, exclude obstructing lesion/foreign body

Periodontal disease + aspiration risk = classic primary lung abscess. Edentulous patients with abscess should prompt search for obstructing lesion or alternative etiology.

Treatment

Antibiotics (first-line)

1. Clindamycin 600 mg IV TID → then 300 mg PO QID (superior to penicillin due to beta-lactamase-producing anaerobes in RCTs)
2. IV beta-lactam/beta-lactamase inhibitor (e.g., ampicillin-sulbactam) → then oral amoxicillin-clavulanate
3. Moxifloxacin 400 mg/d PO - shown as effective as ampicillin-sulbactam in one small study

When Medical Therapy Fails

• 10-20% of patients may not respond (continued fevers, abscess progression)
• Abscesses >6-8 cm are less likely to respond to antibiotics alone
• Options: Percutaneous drainage (risk: pneumothorax, hemothorax, pleural contamination) or surgical resection
• Bronchoscopy for direct cavity drainage may be used

Surgical Indications (Sabiston)

• Persistent cavity ≥2 cm, thick-walled after ≥8 weeks of treatment
• Failure to clear sepsis
• Hemoptysis, rupture into pleural space

Complications

• Empyema - extension to pleural space
• Life-threatening hemoptysis
• Massive aspiration of abscess contents
• Pneumatoceles or bronchiectasis (especially with large initial cavities)
• Recurrence despite therapy

Prognosis

• Harrison's Principles of Internal Medicine 22E (2025)
• Robbins & Kumar Basic Pathology
• Fishman's Pulmonary Diseases and Disorders
• Sabiston Textbook of Surgery