A Stepwise Diagnostic Approach to Cystic Lung Diseases for Radiologists

Lung cysts are commonly seen on computed tomography (CT), and cystic lung diseases show a wide disease spectrum.Thus, correct diagnosis of cystic lung diseases is a challenge for radiologists.As the first diagnostic step, cysts should be distinguished from cavities, bullae, pneumatocele, emphysema, honeycombing, and cystic bronchiectasis.Second, cysts can be categorized as single/localized versus multiple/diffuse.Solitary/localized cysts include incidental cysts and congenital cystic diseases.Multiple/diffuse cysts can be further categorized according to the presence or absence of associated radiologic findings.Multiple/diffuse cysts without associated findings include lymphangioleiomyomatosis and Birt-Hogg-Dubé syndrome.Multiple/diffuse cysts may be associated with ground-glass opacity or small nodules.Multiple/diffuse cysts with nodules include Langerhans cell histiocytosis, cystic metastasis, and amyloidosis.Multiple/diffuse cysts with ground-glass opacity include pneumocystis pneumonia, desquamative interstitial pneumonia, and lymphocytic interstitial pneumonia.This stepwise radiologic diagnostic approach can be helpful in reaching a correct diagnosis for various cystic lung diseases.