Pulmonary cyst

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 ⁵.

Epidemiology

They are generally seen in patients <40 years of age and are associated with a low BMI ⁹.

Pathology

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 ¹.

Differential diagnosis

There are several specific types of thin-walled cystic spaces in the lungs ^6,7:

• 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 ^4-6
• emphysema: lucencies without wall and with central vessel
• cystic bronchiectasis: contiguous with other airways
• occasionally lung cancer may appear as thin walled cystic lung cancer

See also

• cystic lung diseases
• bronchogenic cyst
• congenital pulmonary airway malformation
• cystic pulmonary metastases