*    Radiodiagnosis department, Kasr Alainy teaching hospitals, Cairo university, Egypt;
**  Fetal medicine unit, Cairo university, Egypt;
***Obstetric and gynecology department, National research center, Egypt.

Following images and videos show a case of incomplete non-obstructive cor triatriatum sinister diagnosed during second trimester scan.

A female neonate was delivered spontaneously at 37 weeks of gestation (birth weight of 3040 g and Apgar scores of 8, 9 and 10 at 1, 5 and 10 min, respectively). Postnatal adaptation was uneventful. The mother and her baby were discharged two days after delivery.

Images 1, 2, 3, and videos 1-6: Series of grey scale and color Doppler images and videos showing transverse scans of the fetal heart with a thin membrane within the left atrium dividing the atrium into proximal and distal part (cor triatriatum sinister). Communication between the two parts of the left atrium is large enough and so the dividing membrane does not obstruct the blood flow between the two parts of the left atrium.

Note from the website's editors
Philippe Jeanty, Frantisek Grochal

Image 4: Drawing describing the findings that can be seen in cor triatriatum sinister at the level of the four-chamber-view of the heart. The left atrium is divided into proximal left atrial chamber (PLAC) and distal left atrial chamber (DAC) or vestibule by an obstructing membrane (perforated fibromuscular septum), leaving various size of communication between the two atrial chambers according to the size of perforation of within the obstructing membrane (restrictive versus non-restrictive communication). LV - left ventricle; RV - right ventricle; RA - right atrium.

Finding this membrane is common in prenatal scans, and it represents the remnant of the pulmonary venous sac.