Which condition is pathologically defined as dilation of air spaces distal to the terminal bronchiole?

Emphysema is characterized by the pathological dilation of the air spaces distal to the terminal bronchioles. This condition leads to the destruction of alveolar walls, resulting in a decreased surface area for gas exchange and impaired airflow. The pathogenesis of emphysema often involves chronic irritation of the lung tissue, typically due to inhalation of toxins such as cigarette smoke, which leads to an imbalance between proteases and antiproteases, causing the over-enlargement of the air spaces.

In contrast, chronic bronchitis primarily involves the inflammation of the bronchi, resulting in a productive cough and airway obstruction, but does not specifically refer to the dilation of air spaces. Cystic fibrosis is a genetic condition that affects the lungs and causes mucus accumulation and airway obstruction, rather than the specific air space dilation seen in emphysema. Bronchiectasis is characterized by the abnormal and permanent dilation of the bronchi, often due to infections or obstruction, but again does not refer to the distal air spaces that are impacted in emphysema. Thus, the specific pathological feature of air space dilation in emphysema sets it apart from these other conditions.