A 62-year-old male smoker with a 40 pack-year history presents with progressive dyspnea and cough. Chest X-ray shows hyperinflation with loss of vascular markings in the upper lobes. Which is the most common site of emphysema in this patient?

## Most Common Site of Emphysema in Smokers **Key Point:** Centriacinar (centrilobular) emphysema is the most common pattern of emphysema and is strongly associated with cigarette smoking. ### Pathological Features of Centriacinar Emphysema - Preferential destruction of the **proximal portion** of the respiratory bronchioles - Distal alveoli remain relatively preserved - **Upper lobe and upper zones of lower lobes** are predominantly affected - Correlates with smoking history ### Comparison of Emphysema Subtypes | Type | Site Affected | Association | Pattern | |------|---------------|-------------|----------| | **Centriacinar** | Proximal alveoli of acinus | Cigarette smoking | Upper lobe predominance | | Panacinar | Entire acinus uniformly | Alpha-1 antitrypsin deficiency | Lower lobe predominance | | Paraseptal | Distal alveoli near pleura/septa | Spontaneous pneumothorax | Subpleural location | | Irregular | Around scarred areas | Aging, fibrosis | Scattered distribution | **High-Yield:** The classic teaching is that **smoking → centriacinar emphysema (upper lobes)** and **alpha-1 AT deficiency → panacinar emphysema (lower lobes)**. This distinction is frequently tested. **Clinical Pearl:** The upper lobe predominance in centriacinar emphysema explains why smokers often have apical bullae visible on imaging, increasing risk of spontaneous pneumothorax. ### Why This Patient Has Centriacinar Emphysema 1. 40 pack-year smoking history (strong risk factor) 2. Upper lobe involvement on imaging (characteristic distribution) 3. Progressive dyspnea consistent with smoking-related COPD