Emphysema - Pathology with Pictures

Definition

• Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 635
• Robbins & Kumar Basic Pathology, p. 447

Types of Emphysema

1. Centriacinar (Centrilobular) Emphysema

• Most common type - constitutes >95% of clinically significant cases
• The central/proximal parts of the acinus (respiratory bronchioles) are destroyed; distal alveoli are spared
• Both emphysematous and normal airspaces exist within the same acinus
• Predominantly affects the upper lobes, especially apical segments
• Strongly linked to heavy cigarette smoking

2. Panacinar (Panlobular) Emphysema

• The entire acinus is uniformly enlarged - from respiratory bronchioles to terminal alveoli
• Preferentially affects the lower lobes and anterior lung margins
• Classically associated with α1-antitrypsin (AAT) deficiency (compounded by smoking)

• 80% of homozygous Pi-ZZ patients develop symptomatic panacinar emphysema

3. Distal Acinar (Paraseptal) Emphysema

• The proximal acinus is normal; distal part (adjacent to pleura and lobular septa) is involved
• Characteristic: multiple enlarged airspaces 0.5 mm to >2.0 cm, forming cyst-like structures and bullae
• Clinically important as the cause of spontaneous pneumothorax in young adults

4. Irregular (Paracicatricial) Emphysema

• Irregular acinar involvement; almost always associated with scarring
• Usually clinically insignificant

Pathogenesis

Key Mechanisms:

• Inhaled smoke and noxious particles damage respiratory epithelium and recruit inflammatory cells
• Inflammatory mediators released: LTB4, IL-8, TNF, and others
• Chronic accumulation of neutrophils, macrophages, and CD4+/CD8+ T cells in affected lung

• Inflammatory cells release proteases (especially elastase from neutrophils) that break down elastin and other matrix components
• Normally counteracted by α1-antitrypsin (AAT), the primary elastase inhibitor
• In AAT deficiency (Pi-ZZ genotype, chromosome 14), this protection fails - resulting in unopposed elastin degradation
• Matrix metalloproteinases (MMPs) from macrophages also play a role

• Cigarette smoke and inflammatory cells generate reactive oxygen species (ROS)
• Oxidants cause tissue damage, endothelial dysfunction, and amplify inflammation
• NRF2 (encoded by NFE2L2) is the key cellular sensor/protector against oxidant damage - genetic variants in NRF2 increase susceptibility

• Destruction of elastic tissue in alveolar walls reduces radial traction on surrounding respiratory bronchioles
• Without this traction, bronchioles collapse during expiration - causing functional airflow obstruction even without mechanical blockage

Morphology (Gross and Microscopic)

Gross Pathology

• Advanced emphysema produces voluminous lungs that overlap the heart anteriorly and flatten the diaphragm
• In smoking-related disease, the upper two-thirds of the lungs are most severely affected
• Large alveoli are easily visible on cut sections of fixed lung
• Panacinar emphysema: pale, voluminous lungs that often obscure the heart at autopsy

Bullous Emphysema (Gross)

Microscopic Pathology

• Abnormally large alveoli separated by thin septa with focal centriacinar fibrosis
• Loss of alveolar attachments to the outer wall of small airways
• Pores of Kohn so enlarged that septa appear to "float" or protrude blindly (club-shaped ends)
• Decreased capillary bed area as walls are destroyed
• Advanced: blebs/bullae compressing respiratory bronchioles and vasculature
• Pulmonary hypertension changes from chronic hypoxemia and capillary loss

Summary Table

Complications of Emphysema

1. Respiratory Failure (Acute and Chronic)

• Hypoxemia worsens progressively - initially only on exertion, later at rest
• Hypercapnia develops due to ventilation-perfusion mismatch and loss of alveolar surface area
• Oxygenation deteriorates further during acute exacerbations, exercise, and sleep
• Acute respiratory failure is a major cause of death - often triggered by superimposed bacterial or viral infection

2. Pulmonary Hypertension

• Hypoxic vasoconstriction - chronic alveolar hypoxia causes sustained constriction of pulmonary arterioles
• Loss of capillary bed - destruction of alveolar walls eliminates pulmonary capillaries, reducing the vascular cross-sectional area and raising pulmonary vascular resistance

3. Cor Pulmonale (Right-Sided Heart Failure)

• Right ventricular pressure overload leads first to right ventricular hypertrophy, then to RV dilation and failure
• RV wall may thicken to >1.0 cm (normal ~3 mm)
• The enlarged RV can distort and compress the left ventricle (D-sign on cross-section)
• Clinical signs: peripheral edema, ascites, raised JVP, tricuspid regurgitation
• In pure emphysema, cor pulmonale tends to be a late/end-stage finding (more common and earlier in chronic bronchitis)

4. Secondary (Reactive) Polycythemia

• Chronic hypoxemia stimulates erythropoietin release from the kidneys
• This drives increased red cell production (erythrocytosis/secondary polycythemia)
• Clinically visible as facial vascular engorgement - a clinical sign of severe COPD
• Polycythemia increases blood viscosity, which in turn worsens pulmonary hypertension and raises cardiovascular risk (stroke, thrombosis)

5. Spontaneous Pneumothorax

• Subpleural blebs and bullae (characteristic of paraseptal emphysema and advanced disease) can rupture spontaneously
• Smoking-related emphysema is the most common cause of secondary spontaneous pneumothorax
• Can be acutely life-threatening in a patient with already compromised lung function - even a small pneumothorax can precipitate respiratory failure
• Distinguished from primary spontaneous pneumothorax (young, tall, healthy adults) by its severity and the lack of reserve

6. Acute Exacerbations (AECOPD)

• Superimposed bacterial (e.g., H. influenzae, S. pneumoniae, M. catarrhalis) or viral infections precipitate acute worsening
• Lead to sudden-onset increased dyspnea, worsening gas exchange, and may trigger acute respiratory failure
• A major cause of hospitalization and death in COPD patients
• Mucus plug formation has been shown to cause increased all-cause mortality in COPD

7. Weight Loss and Cachexia

• The increased work of breathing in severe emphysema leads to markedly elevated caloric expenditure
• Combined with poor intake, this produces progressive weight loss that can be so severe as to mimic occult malignancy
• The "pink puffer" phenotype is classically thin and barrel-chested

8. Lung Cancer (Increased Risk)

• Independent of smoking, the chronic inflammatory milieu and structural lung destruction in emphysema is associated with increased lung cancer risk
• Minor hemoptysis in COPD should always raise suspicion for an underlying malignancy

Summary: Complications Cascade

Emphysema
├── Airflow obstruction + gas exchange failure
│   ├── Hypoxemia → secondary polycythemia
│   ├── Hypercapnia → CO₂ narcosis, somnolence
│   └── Acute respiratory failure (death)
│
├── Pulmonary vascular changes
│   ├── Hypoxic vasoconstriction
│   ├── Capillary bed destruction
│   └── Pulmonary hypertension → Cor pulmonale → RHF (death)
│
├── Structural / mechanical
│   └── Bulla/bleb rupture → Pneumothorax (can be fatal)
│
└── Systemic
    ├── Weight loss / cachexia
    ├── Secondary polycythemia
    └── Increased lung cancer risk