Bullous Lung Disease — MD Examination Answer (15 Marks)

1. DEFINITIONS AND TERMINOLOGY

2. CLASSIFICATION OF BULLAE

1. With emphysema — "bullous emphysema" (most common)
2. With pulmonary fibrosis — late-stage sarcoidosis, complicated pneumoconiosis, post-COVID-19
3. Vanishing lung — parenchyma rapidly replaced by multiple bullae
4. Otherwise normal lungs — "bullous lung disease" proper; different etiology and natural history

3. ETIOLOGY AND PATHOGENESIS

• Cigarette smoking (most important)
• α₁-antitrypsin deficiency — measure α₁-AT level in all patients
• Marijuana smoking
• Intravenous drug abuse
• Marfan syndrome / connective tissue disorders (defect in elastin/fibrillin)
• Ehlers-Danlos syndrome (cutis laxa variant with elastase gene defect)

1. Emphysema of distal acini — destruction of alveolar walls → airspace coalescence
2. Scar tissue formation — traps areas of normal lung, enlarges airspaces by traction on surrounding intact alveoli
3. Chronic inflammation — neutrophil-mediated protease/antiprotease imbalance
4. Check-valve mechanism — partial bronchiolar obstruction → progressive air trapping
5. Intravenous drug abuse — talc granulomatosis, septic emboli

4. DISTRIBUTION OF BULLAE

• Intrapleural pressure at apices is more negative than at bases
• Apical alveoli are subjected to greater expanding (distending) stresses
• Radioactive gas studies confirm apical alveoli are considerably larger than basal alveoli at normal lung volumes
• By contrast, panacinar emphysema of α₁-AT deficiency affects lower lobes — a key distinguishing point (Fishman's)
• Paraseptal emphysema (subpleural, upper lobe) → bleb formation → primary spontaneous pneumothorax in young men

5. CLINICAL FEATURES

• Asymptomatic — bullae found incidentally on CXR/CT (small bullae rarely symptomatic)
• Progressive dyspnea — the most common presenting symptom in symptomatic patients; due to compression of adjacent normal lung and wasted ventilation
• Pleuritic chest pain
• Sudden severe breathlessness — secondary spontaneous pneumothorax (rupture) or sudden increase in bulla size
• Fever, cough, purulent sputum — infected bulla

• Usually reflects the overall state of the lungs
• Giant bullae → localized absent breath sounds + increased percussion resonance over the affected area
• In otherwise-normal lungs with small bullae: examination may be normal
• Hyperinflation signs if associated COPD: barrel chest, reduced diaphragmatic excursion

6. INVESTIGATIONS

A. Laboratory

• Hemoglobin/hematocrit — detect anemia (contributing to dyspnea) or secondary polycythemia (chronic hypoxemia)
• α₁-antitrypsin level — mandatory in all patients to detect deficiency
• Arterial blood gases — essential in severe respiratory insufficiency and pre-operative bullectomy assessment; PaCO₂ >45 mmHg = relative contraindication to bullectomy

B. Pulmonary Function Tests (PFTs)

C. Exercise Testing

• Isolated bullous disease (normal lungs): A-a gradient, dead space/tidal volume ratio, and arterial oxygenation remain normal or near-normal with exercise
• Bullae with panacinar emphysema: A-aDO₂ widened at rest and worsens with exercise

D. Imaging

• Hyperlucent area with visible wall (thin hairline shadow)
• Compresses adjacent lung
• May show air-fluid level with infected bulla
• Giant bulla: may mimic pneumothorax — differentiation critical (CXR alone may be unreliable)

• Demonstrates extent, size, number, and distribution of bullae
• Detects underlying emphysema type (centrilobular, panacinar, paraseptal)
• Identifies compressed adjacent parenchyma and its quality (key surgical planning tool)
• Assesses presence of air-fluid levels (infected bulla)
• Detects nodules/mural thickening suggesting malignancy
• 3D reconstruction possible for surgical planning

Bilateral upper lobe bullae on CT — axial and 3D reconstruction views (Fishman's Ch. 50, Fig. 50-5)

• Ventilation-perfusion scintigraphy: bullae show absent ventilation AND absent perfusion
• Helps assess functional contribution of compressed adjacent lung

7. COMPLICATIONS

A. Spontaneous Pneumothorax

• Most important acute complication
• Paraseptal emphysema → bleb rupture → primary spontaneous pneumothorax (typically young, tall men)
• Secondary spontaneous pneumothorax with diffuse bullous emphysema
• Bullae rupture → prolonged air leaks, pleural and parenchymal infections
• Ultrastructural evidence: air leaks through bulla wall with mesothelial cell sloughing; CT density measures suggest valve-like air-trapping mechanism
• Management: Tube thoracostomy → VATS pleurodesis (mechanical abrasion); bullectomy at time of pleurodesis if minimal surrounding emphysema

B. Infected Bulla

• Clinical: Fever, cough, purulent sputum, dyspnea, pleuritic pain, leukocytosis
• Radiology: Air-fluid level within bulla
• Organisms: MRSA, Bacteroides, Pseudomonas aeruginosa, mycobacteria
• Treatment: Empiric antibiotics (as per CAP-COPD regimen); prolonged course; parenteral or intrabulla instillation
• If no improvement → CT-guided percutaneous aspiration (risk: pneumothorax, empyema); tube thoracostomy; endoscopic drainage
• Infected bulla is associated with bronchogenic cancer — follow with interval CXR

C. Bronchogenic Carcinoma

• Significantly increased incidence of lung cancer with bullous disease
• Mechanisms: fibrotic lung predisposition; dystrophic changes; carcinogen retention in poorly ventilated bullae
• CT features suggesting malignancy in bulla:
  • Nodule/mass extruding from bulla wall
  • Nodule confined within bulla lumen
  • Soft tissue thickening of bulla wall
  • Pneumothorax from erosion
  • Air-fluid level
• Classification system (4 types): abutting cyst wall / protruding into lumen / wall thickening / multicystic
• Wall thickening/mural nodule developing after median 35 months on serial CT — surveillance required

D. Haemorrhage

• Rare; may follow air travel (expansion at altitude)

E. Vanishing Lung / Progressive Compression

• Progressive enlargement compresses contralateral normal lung, mediastinal shift

8. SURGICAL MANAGEMENT (BULLECTOMY)

Indications for Bullectomy

• Progressive dyspnea
• Bulla occupying >50% of hemithorax (or >1/3 — giant)
• CT showing compressed but viable adjacent lung
• FEV₁ and DLCO that are discordantly better than expected from CT findings
• Relatively preserved elastic recoil in non-bullous lung

Contraindications to Bullectomy

Pre-operative Assessment

1. Spirometry (FEV₁, FVC, TLC, RV)
2. DLCO
3. ABG
4. HRCT for bulla mapping
5. V/Q scan — assess functional residual lung
6. Echocardiography — exclude pulmonary hypertension
7. Exercise tolerance testing

Surgical Techniques

• Video-Assisted Thoracoscopic Surgery (VATS) — preferred; endoscopic stapling of bullae neck
• Open bullectomy (thoracotomy) — for giant or complex bullae
• Brompton technique — plication and oversewing of bullae without resection (historic)
• Intracavitary drainage — Monaldi procedure (historic, for inoperable patients): drainage tube into bulla via chest wall

Post-operative Results

• Improvement in FEV₁, FVC, exercise capacity, and dyspnea in well-selected patients
• Respiratory muscle strength (maximal inspiratory pressure) improves post-bullectomy
• Best results: isolated giant bulla with preserved surrounding lung; FEV₁ may double
• Poor results: diffuse bilateral emphysema with multiple small bullae

9. KEY DIFFERENTIALS

10. SUMMARY POINTS FOR EXAM

1. Bulla >1 cm; bleb subpleural between visceral pleural layers; cyst has epithelial lining
2. Upper lobe predominance due to greater apical mechanical stress
3. Two major risk factors: cigarette smoking and α₁-AT deficiency
4. Bullous disease = bullae in otherwise normal lungs; different from bullous emphysema
5. DLCO best functional test; discordant preservation (DLCO > expected) = better surgical outcome
6. PaCO₂ >45 mmHg = relative contraindication to bullectomy
7. CT is gold standard for evaluation; V/Q scan assesses adjacent lung function
8. Infected bulla: air-fluid level on CXR; organisms include MRSA, Pseudomonas, mycobacteria
9. Bronchogenic cancer association: wall thickening, mural nodule on CT — surveillance mandatory
10. VATS bullectomy is current standard; best outcome when dominant bulla compresses viable adjacent lung