Malignant neoplasms arising in cystic hamartomas of the lung in childhood.

Cystic lesions of the lung may be developmental or acquired. The authors describe two cases of developmental cystic lung lesions (mesenchymal cystic hamartomas) that harbored unsuspected mesenchymal sarcomas. Although in children the natural history of this lesion is incompletely characterized, there is a definite risk for malignant change. The initial appearance of these cystic lung lesions on the chest radiograph is generally benign. It is important to establish the nature of cystic lung lesions (developmental vs acquired) and recognize the potential risk of malignant change in mesenchymal cystic hamartoma. Cystic lung lesions of uncertain type should be resected.