Der Radiologe
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Areas with reduced density are a common finding with thin-slice computed tomography (CT) examinations of lung parenchyma. Diffuse and localized patterns can be differentiated. The most frequent cause for a diffuse decrease in density is pulmonary emphysema which can be classified into centrilobular, panlobular and paraseptal emphysema based on the distinct anatomical features. ⋯ Langerhans cell histiocytosis and lymphangioleiomyomatosis are the most frequent cystic diseases of the lung parenchyma. Based on the geometry and anatomical distribution of the cysts a differentiation is mostly possible. Rare diseases leading to a reduced lung density include the Birt-Hogg-Dubé syndrome, lymphoid interstitial pneumonia as well as congenital diseases or diseases which are acquired during early childhood, such as cystic adenomatoid malformation or Swyer-James syndrome.