Mesenchymal hamartoma: prenatal and postnatal diagnosis by imaging.

We present a case of a twin pregnancy in which one fetus developed a rapidly growing unilateral intrathoracic tumor. While a cystic adenomatoid malformation was suspected in the ultrasound scan, the magnetic resonance scan suggested a pulmonary blastoma or a bronchioalveolar carcinoma. Postnatal chest radiography and contrast-enhanced computed tomography of the affected newborn were performed, and it was ruled out the possibility of malignant origin. Finally, the anatomopathologic exam revealed the presence of a mesenchymal hamartoma in the chest wall. Nevertheless, parents refused any treatment for the newborn.