What causes a cavitary lung lesion?

Causes of Cavitary Lung Lesions

Cavitary lung lesions result from four primary categories: infections (most commonly tuberculosis, fungal infections, and bacterial abscesses), malignancies (particularly squamous cell carcinoma and metastases), autoimmune/inflammatory conditions (such as granulomatosis with polyangiitis), and pre-existing structural lung disease that becomes secondarily infected. 1, 2

Infectious Causes

Mycobacterial Infections

• Tuberculosis and non-tuberculous mycobacteria (NTM) are predominant risk factors for cavitary disease, particularly for subsequent development of chronic pulmonary aspergillosis 3
• NTM lung disease characteristically presents with nodular/bronchiectatic patterns and can progress to cavitation over months to years 3
• The indolent nature of mycobacterial infections means long-term follow-up (months to years) may be necessary to demonstrate clinical or radiographic changes 3

Fungal Infections

• Aspergillus species cause cavitary lesions through multiple mechanisms: aspergillomas forming within pre-existing cavities, chronic cavitary pulmonary aspergillosis (CCPA) creating new expanding cavities, and subacute invasive aspergillosis in immunocompromised patients 3
• CCPA develops most commonly in pre-existing bronchopulmonary or pleural cavities from prior TB, NTM infection, COPD, or treated lung cancer 3
• The distinctive hallmarks include new and/or expanding cavities of variable wall thickness with or without intracavitary fungal ball formation, often with pleural thickening and marked parenchymal destruction 3
• Aspergillomas present as upper-lobe, solid, round or oval intracavitary masses with the characteristic "air-crescent" sign, mobile on prone positioning 3
• Endemic fungi including Histoplasma and Coccidioides should be considered based on geographic exposure 4, 5

Bacterial Infections

• Common bacterial pathogens causing cavitation include Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus pneumoniae, and Haemophilus influenzae 6
• Pseudomonas aeruginosa causes cavitation in 4-15% of severe pneumonia cases and requires specific antimicrobial coverage 4
• Lung abscesses from septic emboli often involve mixed anaerobic flora, requiring cultures specifically for anaerobes 4
• Acinetobacter represents a rare but increasingly recognized cause of rapid cavitary lesion development, particularly following COVID-19 infection 6

Malignant Causes

Primary Lung Cancer

• Malignancy is a leading cause of cavitary lesions in adults, particularly in patients with thick cavity walls, older age, smoking history, and hemoptysis 3, 1, 2
• Squamous cell carcinoma most commonly cavitates among primary lung cancers 7, 8
• High-grade mucoepidermoid carcinoma can present as a cavitary lesion with extensive central necrosis, potentially mimicking infectious processes 9
• Necrotic lung carcinoma can mimic aspergilloma radiographically 3

Metastatic Disease

• Multiple lesions of varying size are most likely malignant, particularly in patients with known primary tumors 3
• Metastases should be considered in the differential, especially with multiple cavitary nodules 3, 1

Autoimmune and Inflammatory Causes

• Granulomatosis with polyangiitis (Wegener's granulomatosis) causes cavitary nodules as part of systemic vasculitis 3, 1, 2
• Rheumatoid nodules can cavitate and may be pure rheumatoid nodules or contain Aspergillus superinfection 3, 1
• Other granulomatous diseases including sarcoidosis (particularly fibrocystic sarcoidosis) predispose to cavity formation 3

Pre-existing Structural Lung Disease

• COPD, prior pneumothorax, bronchiectasis, and ankylosing spondylitis create structural abnormalities that predispose to secondary infection and cavitation 3
• Pneumoconiosis and progressive massive fibrosis in silicosis provide substrate for cavity development 3
• Congenital malformations represent the most common cause of cavitary lesions in children, contrasting with the adult pattern 8

Critical Diagnostic Considerations

The clinical context dramatically narrows the differential diagnosis:

• Thick-walled cavities with irregular margins suggest malignancy, while thin-walled cavities with air-fluid levels suggest infection 2
• Upper lobe predominance suggests tuberculosis, NTM, or aspergillosis 3
• Multiple cavities with surrounding consolidation suggest bacterial infection or septic emboli 2, 4
• Chronic cavitary lesions present for >3 months require evaluation for chronic pulmonary aspergillosis, especially with positive Aspergillus serology 2

Common pitfall: The presence of one pathogen (such as M. tuberculosis) should not preclude evaluation for concurrent malignancy, as both can coexist 9