Pulmonary cyst

A Pulmonary cystspulmonary cyst are roundis any well-circumscribed gas-containing structure within lung parenchyma with a thin, thin-walled, low attenuation spaces/lucencies in the lungtypically regular wall. Lung cysts usually contain air but occasionally alsoOccasionally a cyst may contain fluid or solid material instead of gas ⁵¹⁰.

Terminology

The term ‘cystic’ is used to denote lesions with central gas attenuation contained by a wall, regardless of aetiology. 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.

Epidemiology

TheyA few cysts may develop with ageing and 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. 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.

Differential diagnosis

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

• bleb: pleural/subpleural, ≤1-2usually < 1 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