Congenital pulmonary airway malformation, formerly known as congenital cystic adenomatoid malformation, is a rare multicystic, intralobar mass of disorganized lung tissue, most often seen in the lower lobes. It is usually diagnosed in children but can be left unrecognized until adulthood.

It can be categorized into three subtypes on the basis of its appearance:

• type 1 is most frequent and consists of multiple cysts 2 cm or greater in diameter; on CT, the disease appears as a large, air-filled multicystic lesion
• type 2 is defined as multiple cysts smaller than 2 cm
• type 3, the least frequent type, there are numerous microscopic cysts that often have a more solid appearance on imaging

Complications of congenital pulmonary airway malformation include infection and malignant transformation. Treatment of congenital cystic lesions usually consists of simple resection of the involved tissue or lobectomy.