Congenital high airway obstruction syndrome without tracheoesophageal fistula and with in utero decrease in relative lung size.

Congenital high airway obstruction syndrome (CHAOS) is diagnosed by characteristic features on US and MRI including fetal upper airway occlusion, lung hyperinflation with an inverted diaphragm, and sometimes massive ascites and hydrops. We describe a case of CHAOS in which improvement in the fetal condition was observed on three sequential fetal MRIs. Such an improvement was thought to represent decrease in intrathoracic pressure caused by a spontaneous perforation such as a tracheoesophageal fistula. However, a fistula was not observed in the present case. Therefore, we suggest that imaging improvements in patients with CHAOS do not always correspond to the presence of a fistula and other factors might contribute to decreasing fetal intrathoracic pressure.