▶ Based on the CT features, the differential consists of cystic adenomatoid malformation, cystic intralobar sequestration, or postinfectious pneumatoceles.
▶ Cystic adenomatoid malformation is a congenital lesion with abnormal bronchiolar proliferation. The “cysts” are actually massively dilated bronchioles.
▶ The Stocker classification system divides these lesions into type I (large cysts >2 cm), type II (multiple small cysts <2 cm), and type III (solid, microcystic lesions). Type II and III lesions have been associated with a poor prognosis, probably from their frequent association with other congenital anomalies. Type I lesions do have a low likelihood of developing malignancies, such as bronchoalveolar carcinoma.
▶ The majority of lesions are detected in childhood as masses on chest radiographs in infants with respiratory distress. Initially, the lesion may appear solid, but over the first 24 to 48 hours of life fluid clears from the lesion, leaving cystic airspaces. In older children or adults, these lesions can be encountered incidentally or come to attention due to mass effect or superinfection.
Bush A. Congenital lung disease: a plea for clear thinking and clear nomenclature. Pediatr Pulmonol. 2001 Oct;32(4):328-337.Find this resource: