Chiari"s network

https://sonoworld.com/TheFetus/Case.aspx?CaseId=2657&answer=1

The arrow points at the echogenic structure within the right atrium, representing the Chiari"s network

. An abnormal resorption of the right valve of the sinus venosus (which serves to direct the blood in embryonic life from the inferior vena cava to the fossa ovalis) results in Chiari"s network within the right atrium. The image 12 represents a drawing of the transverse plane of the fetal thorax at the level of the four chamber view. Position of the Chiari"s network is visible within the right atrium (Chiari"s network may have variable appearance ranging from the a few thin fibers to a membrane-like structure). RA - right atrium, RV - right ventricle, LV - left ventricle, LA - left atrium, Ao - descending aorta).