Paraseptal Emphysema

History: 55 year old male with history of hypertension and diabetes presents with shortness of breath. 

Single axial CT scan through the chest shows multiple peripherally based, well demarcated lucencies with thin, well-defined walls.

This is the typical appearance of paraseptal emphysema, which is caused by destruction of alveolar ducts and alveoli in the periphery of the secondary pulmonary lobules. When these lucencies become larger than 10 mm, they are classified as bullae. Having bullae put you at risk for a spontaneous pneumothorax, and particularly pneumothorax when flying.