Conditions That Cause Lung Blebs
Blebs and bullae in the lungs are primarily caused by smoking-related lung disease, alpha-1 antitrypsin deficiency, and idiopathic mechanisms in otherwise healthy individuals, with subpleural blebs found in up to 90% of primary spontaneous pneumothorax cases. 1, 2
Primary Spontaneous Pneumothorax (Otherwise Healthy Lungs)
Subpleural blebs and bullae occur in up to 90% of primary spontaneous pneumothorax cases at thoracoscopy/thoracotomy and in up to 80% on CT scanning, despite the absence of underlying pulmonary disease. 1, 2 The pathogenesis of these bullous changes in apparently healthy lungs remains unclear, though several factors contribute:
- Smoking is the dominant risk factor: Lifetime risk of pneumothorax in healthy smoking men reaches 12% compared to 0.1% in non-smoking men. 1
- Genetic predisposition plays a significant role: Multiple common and rare genetic variants are associated with increased susceptibility to lung blebs. 2
- Paraseptal emphysema occurs close to connective tissue septae and leads to blebs on the lung surface, predisposing to pneumothorax or giant bullae. 2
Alpha-1 Antitrypsin (AAT) Deficiency
AAT deficiency causes panacinar emphysema with basal predominance and is associated with bullae formation, though bullae are actually more common in usual (non-AAT deficiency) emphysema. 1
Key diagnostic considerations for AAT deficiency:
- Test all patients with early-onset pulmonary emphysema (with or without smoking history) for AAT levels. 1
- Test all subjects with COPD or asthma with incompletely reversible airflow obstruction once for quantitative AAT determination. 1
- Large bullae, preferentially in the basal parts of the lungs, are occasionally described at autopsy, in surgical specimens, or on X-ray. 1
- On HRCT, the classic finding is panacinar emphysema with uniform abnormally low attenuation of lobules and predominant lower lobe distribution. 1
Chronic Obstructive Pulmonary Disease (COPD)
Emphysematous bullae develop in COPD patients, particularly those with severe disease and marked air trapping. 1
- Chest radiography can identify emphysematous bullae and help exclude other diagnoses like lung cancer. 1
- Large or expanding bullae may require surgical removal or ablation in selected patients, potentially leading to prolonged improvements in FEV1. 1
- History of previous pneumothorax or presence of emphysematous bullae suggests risk of further pneumothorax with pressure changes (e.g., air travel). 1
Bronchiectasis-Associated Blebs
Bronchiectasis can be associated with bullous changes, though the relationship is complex:
- AAT deficiency shows bronchial wall thickening and/or dilation in 41% of patients and bronchiectasis in 43%. 1
- Bronchiectasis may result more from emphysematous changes in the parenchyma than from AAT deficiency per se. 1
- Multiple underlying causes of bronchiectasis (cystic fibrosis, primary ciliary dyskinesia, connective tissue disorders) can predispose to bullous changes. 3
Bullous Emphysema Without Typical Risk Factors
Rare cases of bullous emphysema occur in nonsmokers without genetic predisposition, where environmental exposure is often overlooked. 4 These cases emphasize the importance of:
- Comprehensive environmental exposure history
- Recognition that etiology includes both tobacco smoking and alpha-1 antitrypsin deficiency as primary causes 4
Clinical Implications
CT scanning is far more sensitive than plain chest radiography for detecting blebs and bullae, with pathological lung changes found in 89% (31/35) of primary spontaneous pneumothorax patients on CT versus only 31% (11/35) on chest X-ray. 5
Strong emphasis must be placed on smoking cessation, as smoking significantly increases pneumothorax risk in those with genetic lung blebs. 1, 2
Genetic testing and counseling should be offered to patients with suspected genetic predisposition, particularly those with family history of pneumothorax, and first-degree relatives should receive genetic counseling. 2