Cystic masses of the pediatric lung: update on congenital pulmonary airway malformation and its differential diagnosis.

Localized cystic lung lesions in pediatric patients encompass a spectrum of benign and rare malignant conditions that are quite distinct from cystic lung disease arising in adulthood. The majority have historically fallen under the diagnostic category of "congenital pulmonary airway malformation," a term that has been used to denote a diverse group of diseases ranging in etiology from ectopia to bronchial atresia to mosaic oncogenic mutation or neoplasia. This article reviews the clinical characteristics, gross and histologic features, and pathogenetic underpinnings of congenital pulmonary airway malformation as well as lesions that enter its histologic differential diagnosis. In light of ongoing advances in the field, previously proposed pathology-based classification schemes are critically appraised, and a new diagnostic framework is considered.