Pulmonary cysts are round, thin-walled, low attenuation spaces/lucencies in the lung. Lung cysts usually contain air but occasionally also contain fluid or solid material .
In contradistinction to all other organs, the term cyst as used in the lung is a misnomer, as it usually refers to a contained focus of gas, not fluid.
Pulmonary cysts can be congenital or acquired. Multiple lung cysts in a child may be associated with an underlying process although this is rare, e.g. pleuropulmonary blastomas .
There are several specific types of thin-walled cystic spaces in the lungs :
- bleb: pleural/subpleural, ≤1-2 cm diameter
- bulla: pleural/subpleural, ≥1-2 cm diameter
- honeycombing: subpleural stacks of cysts, typically 3-10 mm diameter with walls 1-3 mm in thickness
- pneumatocele: usually transient cystic airspace within the lung, usually due to pneumonia or trauma
There are several mimics of pulmonary cysts:
- pulmonary cavity: surrounded by mass, nodule, or consolidation, creating wall thickness >2-4 mm
- emphysema: lucencies without wall and with central vessel
- cystic bronchiectasis: contiguous with other airways