Congenital cystic adenomatoid malformation.

Congenital cystic adenomatoid malformation of the lung is a rare lesion that typically manifests as neonatal respiratory distress secondary to progressive expansion of the affected lung. Three distinct types have been described based on the size of the cysts and the microscopic appearance. Type I lesions are characterized by large cysts of varying sizes (measuring more than 2 cm in diameter), type II lesions typically contain cysts of a more uniform size (not exceeding 2 cm in diameter), and type III lesions contain microscopic cysts. Radiologic findings include single or multiple large cysts, multiple small cysts of uniform size, and solid-appearing masses. The treatment of choice is excision of the affected lobe. The prognosis is favorable in the absence of pulmonary hypoplasia, fetal hydrops, or associated congenital anomalies.