Pulmonary cyst

Last revised by Liz Silverstone on 6 Mar 2024

A pulmonary cyst is any well-circumscribed gas-containing structure within lung parenchyma with a thin, typically regular wall. Occasionally a cyst may contain fluid or solid material instead of gas 10.

The term ‘cystic’ is used to denote lesions with central gas attenuation contained by a wall, regardless of etiology. The wall thickness and regularity may vary. The morphology of cystic lesions such as blebs, bullae and cysts overlaps and there are no objective criteria to quantify wall thickness and no consensus regarding definitions 10.

A few cysts may develop with aging and are generally seen in patients >40 years of age with a low BMI 9.

Pulmonary cysts can be congenital or acquired and can be caused by:

  • check-valve obstruction with distal airspace dilatation

  • bronchial wall necrosis

  • protease-mediated parenchymal destruction 10

Multiple lung cysts in a child may be associated with an underlying process although this is rare, e.g. pleuropulmonary blastomas 1.

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

  • bleb: pleural/subpleural, usually < 1 cm diameter

  • bulla: pleural/subpleural

  • 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:

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