Intermittent 'double bubble' sign in a case of congenital pyloric atresia.

We report a case of congenital pyloric atresia in which two cystic masses in the fetal upper abdomen and polyhydramnios were observed from 24 weeks' gestation to term. The two cystic masses were thought to indicate the 'double bubble' sign in utero, leading to a misdiagnosis of congenital duodenal obstruction. At 33 weeks' gestation, continuous ultrasound observation of the two cystic masses was made for 60 min. During the periods when gastric peristalsis was absent, the 'double bubble' sign was observed. However, during the periods when gastric peristalsis was present, the 'double bubble' sign disappeared. In retrospect, both cystic masses were stomach and the 'double bubble' sign disappeared with peristalsis of the antrum. In order to differentiate from congenital duodenal obstruction, whole stomach configuration should be delineated by continuous observation covering periods when gastric peristalsis is active as well as quiet.