Cystic lung disease.

This review addresses the pathology of lung disease in which the predominant finding is diffuse cystic change. Although cysts may be found radiologically in a wide variety of disease states, the entities discussed are those most likely to be encountered in biopsies where the underlying aetiology is unclear. These include Langerhans cell histiocytosis, lymphangioleiomyomatosis and Birt-Hogg-Dubé syndrome, and recent advances in the molecular pathology of these entities are reviewed. Conditions in which cyst formation may occur but does not represent the predominant pathology are also considered, including alveolar septal amyloidosis, light chain disease, follicular bronchiolitis and lymphocytic interstitial pneumonia. Cystic metastases may present a differential diagnostic dilemma.