A 35-year-old multigravida was referred at 21.2 weeks of gestation due to a suspected large mass in the left thoracic cavity, accompanied by fetal ascites.
Ultrasonography revealed a 53 x 38 mm hyperechoic lesion in the left thoracic cavity with an inverted diaphragm. The mass was supplied by the pulmonary circulation.
The heart was severely compressed to the right. Skin edema and extensive ascites were observed, indicative of fetal hydrops.
Based on these findings, congenital pulmonary airway malformation (CPAM) or unilateral bronchial atresia was suspected. At 25 weeks of gestation, magnetic resonance imaging confirmed a diagnosis of left unilateral bronchial atresia.
The baby was delivered at 31 weeks following preterm premature rupture of membranes.
The neonate weighed 1,540 g at birth and had poor Apgar scores. A postnatal X-ray revealed total haziness of the left lung, and the neonate died three days after birth.
Unlike congenital high airway obstruction syndrome (CHAOS), which typically presents with symmetrically enlarged both lungs and increased echogenicity, unilateral bronchial atresia results in massive enlargement of only one lung.
This condition may mimic more commonly encountered unilateral fetal lung abnormalities, particularly microcystic CPAM or pulmonary sequestration.

Keywords: bronchial obstruction