Basic HRCT Patterns: Cysts

Definition: The term cyst refers to a rounded structure that is filled with air and usually has a thin wall. Because the inside of a cyst contains no lung parenchyma or other material, the contents of a cyst should appear darker than normally aerated lung and comparable to the air in the tracheobronchial tree or surrounding the patient.

How to Recognize Cysts

This image shows multiple thin-walled cysts clustered together in the left lower lobe.

Compare the appearance of the cyst contents with the normal right lung parenchyma and the air surrounding the patient (seen at the four corners of the image).

The cyst contents are as dark as air surrounding the patient. In this case, the cysts represent multiple dilated bronchi (known as cystic bronchiectasis) in a patient with chronic sputum production since a pneumonia in childhood.

Pulmonary cysts of cystic bronchiectasis are often clustered together and focal. In contrast, multiple cysts confined to the subpleural lung are usually indicative of honeycombing, which results from chronic interstitial fibrosis. Cystic lung disease also occurs in Langerhans' cell histiocytosis and lymphangioleiomyomatosis.

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Hyaline membranes

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Type II cell hyperplasia

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Protein-rich edema fluid

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