Cystic lung disease: achieving a radiologic diagnosis.

Diffuse cystic lung disease represents a diverse group of uncommon disorders with characteristic appearance on high resolution CT imaging. The combination of imaging appearance with clinical features and genetic testing where appropriate permits a confident and accurate diagnosis in the majority of the diseases without recourse for open lung biopsy. The mechanism of cyst development disease is unclear but in some disorders appears to be related to small airways obstruction. These diseases are incurable, with the exception of Langerhans cell histiocytosis which may spontaneously remit or resolve on smoking cessation. Disease progression is unpredictable; in general older patients have a more benign disease, while young patients may progress rapidly to respiratory failure. An understanding of the complications of cystic lung disease and the appearance of disease progression is essential for the management of these patients. A number of these disorders are associated with malignancy, recognition of the potential tumors permits appropriate imaging surveillance. Due to the widespread use of CT, pulmonary cysts are increasingly discovered incidentally in an asymptomatic individual. The diagnostic challenge is to determine whether these cysts represent an early feature of a progressive disease or have no clinical significance. In the elderly population the cysts are unlikely to represent a progressive disease. In individuals <50 years further evaluation is recommended.