Prenatal diagnosis of atrial septal aneurysm

We report the prenatal diagnosis of fetal atrial septal aneurysm based on the observation of a fluttering flap in the left atrium. The aneurysm was associated with an interatrial communication. In a 4-chamber view, separate arms of the aneurysm could be seen contracting in and extending out in response to the fetal cardiac cycle, giving the fluttering appearance of a jellyfish. The aneurysm disappeared 1 month after birth with no complications. The findings in this case indicate that isolated atrial septal aneurysm is a natural transient phase of spontaneous closure of the foramen ovale during normal fetal development.