Diffuse cystic lung diseases.

Diffuse cystic lung diseases are uncommon but can present a diagnostic challenge because increasing number of diseases have been associated with this presentation. Cyst in the lung is defined as a round parenchymal lucency with a well-defined thin wall (< 2 mm thickness). Focal or multifocal cystic lesions include blebs, bullae, pneumatoceles, congenital cystic lesions, traumatic lesions, and several infectious processes such as coccidioidomycosis, Pneumocystis jiroveci pneumonia, and hydatid disease. "Diffuse" distribution in the lung implies involvement of all lobes. Diffuse lung involvement with cystic lesions can be seen in pulmonary lymphangioleiomyomatosis, pulmonary Langerhans' cell histiocytosis, lymphoid interstitial pneumonia, Birt-Hogg-Dubé syndrome, amyloidosis, light chain deposition disease, honeycomb lung associated with advanced fibrosis, and several other rare causes including metastatic disease. High-resolution computed tomography of the chest helps define morphologic features of the lung lesions as well as their distribution and associated features such as intrathoracic lymphadenopathy. Correlating the tempo of the disease process and clinical context with chest imaging findings serve as important clues to defining the underlying nature of the cystic lung disease and guide diagnostic evaluation as well as management.