The following theories have been proposed as to the mechanism of post pneumonic pneumatocele formation; however, the exact mechanism remains controversial.
1. The initial event is inflammation, with narrowing of the bronchus, leading to the formation of an endobronchial ball valve. Ultimately, this bronchial obstruction leads to the distal dilatation of the bronchi and alveoli.
2. A peribronchial abscess forms and subsequently ruptures its contents into the bronchial lumen. This also acts similarly to a ball-valve obstruction in the bronchus and leads to distal dilatation.
3. Pneumatoceles are caused by bronchial inflammation that ruptures the bronchiolar walls and causes the formation of "air corridors." Air dissects down these corridors to the pleura and forms pneumatoceles, a form of subpleural emphysema.